Pistons and Rings

July 13, 2014

Contents:    1. Rings    2. Ring Info    3. Pistons     4. Piston Info

 


1. Piston Rings

Piston ring types R, T, L and gap styles FG, GI

GI gap style
pin in center of groove

 

 

 

 

 

FG gap style (aka GN)
pin on side of groove

Meanings:
size
is the cylinder diameter that the ring would have a 0.004 to 0.008″ gap in
height is the thickness up-and-down. T & L rings have 2 heights, outer & inner
width is the depth inward-and-out. L rings have two widths, outer and inner
type R = Rectangular  “square”  shape (cross-section)
type L = L-shape  aka  “Dykes”  shape (cross-section)
type T = Trapezoidal “slant top” shape (cross-section)
gap FG Foro Grano = GN Grano Normale gap style is for pin on side of groove
gap GI Grano Interno = gap style is for ring pin in center of piston ring groove
price is for each ring, unless noted.  All rings are for 50cc engines, unless noted.

0  size x height x width  type gap price     part number  applications
36.50
 x 1.50 1./x 1.7/0.7  R  FG $10.0 0 0000  222812 Tomos MC36 36cc
38.00 x 1.50 1./x 1.7/0.7  R  G I $10.0 0 0215.100.100 Sachs 1979-later 504, 505 1C,1D (upper only)
38.00 x 1.50 1./x 1.7/0.7  R  G I $10.0 00.. 000000000 Zanetti (front engine)
38.00 x 1.5/1.3 x 1.60 /7  T  FG $17.0 0..0000 223707 Tomos A55 (2001-06) superseded in ’07 to 236802
38.00 x 1.50 1./x 1.7/0.7  R  FG $10.0 0..0000 236802 Tomos A35 (1991-06), Tomos A55 (2007-on)
38.00 x 1.50 1./x 1.7/0.7  R  FG $10.0 0 000.672.5110 Derbi 1976-1986 (lower only), Odyssey, Solo
38.00 x 2.0/1.0 x 1.5/0.5  L  G I $10.0 0 000.802.5110 Derbi 1976-1986 (upper ring) fits Puch loose inner
38.00 x 2.0/1.0 x 1.7/0.7  L  G I $23.0 0 328.110.9601 Puch 1979-1980 deluxe models upper
38.00 x 2.00 1./x 1.7/0.7  R  FG $10.0 0 331.110.1601 Puch rounded edge for Al cylinder
38.00 x 2.00 1./x 1.7/0.7  R  FG $10.0 0 320.110.0601 Puch sharp edge for Fe cyl except 79-80 deluxe upper
38.00 x 2.00 1./x 1.7/0.7  R  FG $10.0 0 0215.009.000 Sachs 504, 505 1A,1B (both) 1C,1D (lower only)
38.00 x 2.00 1./x 1.7/0.7  R  FG $10.0 0..0000 044754 Tomos A3 1975-1990
38.00 x 2.00 1./x 1.7/0.7  R  FG $10.0 00.000 26.1001 Morini S5K, S5K2
38.00 x 2.50 1./x 1.7/0.7  R  FG $12.0 71.0802.0 4600 Minarelli V1 1hp 20mph, Sears Allstate, early Puch
38.00 x 2.50 1./x 1.7/0.7  R  flat  N/A     0.000 0000000 Solex 45cc 1946-1954
38.20 x 1.50 1./x 1.7/0.7  R  FG $10.0 0..0000182518 Vespa 79-later & some 78s lower ring
38.20 x 1.50 1./x 1.7/0.7  R  FG $10.0 0 000.672.2511 Derbi 1st oversize lower
38.20 x 2.00 1./x 1.7/0.7  R  FG $16.0 00..000 166945 Vespa 78-80 USA-type, must file down a 077775
38.00 x 2.00 1./x 1.7/0.7  R  FG $10.0 0000.0 26.1002 Morini S5K, S5K2 1st oversize
38.20 x 2.0/1.0 x 1.8/.75  L  G I $14.0 0..0 000182519 Vespa 79-later & some 78s upper ring
38.20 x 2.0/1.0 x 1.5/0.5  L  G I  N/A   000.802.5110 Derbi 1st o.s for 1976-1986 upper ring
38.40 x 1.50 1./x 1.7/0.7  R  FG $14.0 00 000  132515 Vespa 1st oversize lower ring, 79-later & some 78s
38.40 x 1.5/1.3 x 1.60 /7  T  FG  N/A    0 000   3010010 Kinetic TFR (Vespa Si remake) 95-later
38.40 x 2.00 1./x 1.7/0.7  R  FG $12.0 0 0000  077775 Vespa 77-earlier & some 78s, early Kinetic
38.40 x 2.0/1.0 x 1.8/.75  L  G I  N/A    0 000   G.68473 Vespa 1st oversize upper ring, 79-later & some 78s
38.50 x 1.50 1./x 1.7/0.7  R  FG $12.0 0 0000  227758 Tomos 1st oversize for A35
38.50 x 2.00 1./x 1.7/0.7  R  FG $10.0 0 0000  044751 Tomos 1st oversize for A3
38.60 x 2.00 1./x 1.7/0.7  R  FG $14.0 0 00000  98196 Sachs 1st o.s for 504, 505, 2nd o.s Vespa 79- lower
38.70 x 1.50 1./x 1.7/0.7  R  FG $17.0 71.0803.0 4635 Minarelli V1 1.5, 2hp 25, 30mph (after 1979)
38.80 x 2.0/1.0 x 1.65/.6  L  G I $26.0 .0  4.7470.5140 Demm Smily upper
38.80 x 1.50 1./x 1.7/0.7  R  FG $10.0 71.0805.0 4640 Minarelli V1 1.5, 2hp 25, 30mph (until 1979)
38.80 x 2.00 1./x 1.7/0.7  R  FG  N/A    .0  4.7470.5100 Demm Smily lower
39.00 x 2.0/1.0 x 1.65/.6  L  G I $24.0 0.000   26.1003 Morini S5R, S5T, S5E, S5ET kids off road, upper
39.00 x 1.00 1./x 1.7/0.7  R  FG $19.0 0.000   26.1060 Morini S5N, S5GS, others, some LEM dirt bikes
39.00 x 1.50 1./x 1.7/0.7  R  FG $25.0 71.0855.7 4650 Minarelli 1st o.s for V1 1.5, 2hp 25, 30mph
39.00 x 1.50 1./x 1.7/0.7  R  FG  $25.0 00.00  26.1044 Morini S5R, S5T, S5E, S5ET kids off road, lower
39.00 x 2.00 1./x 1.7/0.7  R  G I $12.0 00 0000  22148 Motobecane (GI after June 1976)
39.00 x 2.00 1./x 1.7/0.7  R  FG  N/A    00 0000  22148 Motobecane (FG before July 1975), DiBlasi mini-cycle
39.00 x 2.0/1.0 x 1.8/0.7  L  G I  N/A    00000  26-1003 Morini S5R, S5T alum. cylinder (upper ring)
39.03 x 2.00 1./x 1.7/0.7  R  G I $14.0 00 00  2812200 Jawa 207 1970-83 standard
39.20 x 1.50 1./x 1.7/0.7  R  FG $15.0 71.0855.7 4660 Minarelli 2nd o.s for V1 1.5, 2hp 25, 30mph
39.28 x 2.00 x 1.65 /0..7  R  G I $14.0 00 00  2812201 Jawa 207 1970-83 1st oversize
39.40 x 1.50 1./x 1.7/0.7  R  FG  N/A    71.0855.7 4670 Minarelli 3rd o.s for V1 1.5, 2hp 25, 30mph
39.40 x 1.50 1./x 1.7/0.7  R  G I  N/A    000 0  0000000 Aermacchi Harley Davidson M50 std 1965-66
39.40 x 2.50 1./x 1.7/0.7  R  FG  N/A    000 0  0000000 Rizzato Califfo 1978 standard
39.50 x 1.70 x 1.60 /0..7  R  flat $10.0 00 0000  60817 Solex rings (3) no locating pins
39.53 x 2.00 x 1.65 /0..7  R  G I $19.0 00 00  2812202 Jawa 207 1970-83 2nd oversize
39.60 x 1.50 1./x 1.7/0.7  R  FG $17.0 71.0855.7 4680 Minarelli 4th o.s for V1 1.5, 2hp 25, 30mph
39.80 x 1.50 1./x 1.7/0.7  R  FG $17.0 71.0855.7 4690 Minarelli 5th o.s for V1 1.5, 2hp 25, 30mph
39.80 x 2.50 1./x 1.7/0.7  R  FG  N/A    000 0  0000000 Rizzato Califfo first oversize
40.00 x 1.2/1.0 x 1.60 /7  T  FG $15.0 000 00  633086 China 49cc two-strokes most
40.00 x 1.2/1.0 x 1.70 /7  T  G I $16.0 000 0  0633086 PGO Star 50 upper, other Asian 49cc
40.00 x 1.20 x 1.85 /0..7  R  G I $14.0 00 00  2812202 PGO Star 50 lower, others
40.00 x 1.5/1.3 x 1.80 /7  T  FG $15.0  13011.147.005 Dailim Trac, upper for Honda NC50,PA50,Yamaha QT50
40.00 x 1.50 1./x 1.7/0.7  R  FG $10.0 00 0000  55196 Batavus M48, M56, Trac (not Daelim), Flandria 
Bermuda
40.00 x 1.50 1./x 1.7/0.7  R  FG $10.0  13011.147.005 Honda lower for NC50,PA50, Yamaha QT50 lower
40.00 x 1.50 1./x 1.7/0.7  R  FG $10.0 000000   G7347 Benelli G2, 1965-75 Ward Riverside, Benelli mini-cycles
40.00 x 1.50 1./x 1.7/0.7  R  FG $10.0 00000  26-1044 Morini S5R, S5T alum. cylinder (lower ring)
40.00 x 1.50 1./x 1.7/0.7  R  G I $12.0 00000   551913 Verona (like Morini MO-1 but 40.0mm not 40.4)
40.00 x 1.50 1./x 1.7/0.7  R  G I $12.0    0F0.250.0111 Derbi 1986-1989 flat reed, Kreidler Flory
40.00 x 2.00 1./x 1.7/0.7  R  FG $12.0 00   307.021.00 Garelli all 1970’s, 00’s Avanti/Mont (most)
40.00 x 2.00 1./x 1.7/0.7  R  FG $12.0 00   307.021.00 Casal K177, 2000’s Hero Majestic Pacer
40.00 x 2.50 1./x 1.7/0.7  R  G I $15.0 0000 00  38315 Peugeot 102, 103 (almost all US models)
40.20 x 1.50 1./x 1.7/0.7  R  FG $22.0 0000   G7347/2 Benelli 3o.s, M Ward 3o.s, filed down 40.25
40.20 x 2.00 1./x 1.7/0.7  R  FG $14.0 00   308.027.00 Garelli 1st oversize
40.25 x 1.00 1./x 1.7/0.7  R  FG $13.0 000..000 00000 China 1st o.s for 49cc two-stroke scooter
40.25 x 1.5/1.3 x 1.80 /7  T  FG  N/A     13021.147.005 Honda 1st o.s NC50,PA50 upper
40.25 x 1.50 1./x 1.7/0.7  R  FG $15.0 00 000  480511 Batavus 1st o.s, Honda 1st os NC50,PA50 lower
40.30 x 1.50 1./x 1.7/0.7  R  FG $20.0 000000   4641b Minarelli V1HL and V1L lower, filed down 40.5
40.30 x 2.0/1.0 x 1.8/0.7  L  G I 
N/A    000000   4641a Minarelli V1L upper
40.40 x 1.50 1./x 1.7/0.7  R  FG  N/A    0000   G7347/4 Benelli 2nd o.s for G2, M Ward and mini-cycles
40.40 x 1.50 1./x 1.7/0.7  R  G I $10.0 00 00   26-1045 Morini MO1, MO2, M1 engines

40.40 x 2.00 1./x 1.7/0.7  R  FG $12.0 0 0  308.028.00 Garelli 2nd oversize
40.50 x 1.5/1.3 x 1.80 /7  T  FG  N/A     13031.147.005 Honda 2nd o.s NC50,PA50 upper
40.50 x 1.50 1./x 1.7/0.7  R  FG $12.0  13031.147.005 Batavus 2o.s, Honda 2o.s NC50,PA50 lower
40.50 x 2.50 1./x 1.7/0.7  R  G I $12.0 00 0000  33648 Peugeot 102, 103 (some, but none in CA)
40.60 x 1.50 1./x 1.7/0.7  R  FG  $20.0 0000  G7347/6 Benelli 3o.s, M Ward 3o.s, filed down 40.8
40.60 x 1.50 1./x 1.7/0.7  R  FG  N/A    000000   4651b Minarelli 1st oversize for V1L lower
40.60 x 1.50 1./x 1.7/0.7  R  G I $15.0 000  26-1046/6 Morini 1st o.s for MO1, MO2, M1 engines
40.60 x 2.00 1./x 1.7/0.7  R  FG $10.0 0 0  308.029.00 Garelli 3rd oversize
40.60 x 2.0/1.0 x 1.65/.6  L  G I $15.0 000000    4651a Minarelli 1st o.s for V1L upper
40.75 x 1.5/1.3 x 1.80 /7  T  FG  N/A     13041.147.005 Honda 3rd o.s NC50,PA50 upper
40.75 x 1.50 1./x 1.7/0.7  R  FG  N/A     13041.147.005 Honda 3rd o.s NC50,PA50 lower
40.80 x 1.50 1./x 1.7/0.7  R  G I $12.0 000   26.1046/8 Morini 2nd o.s for MO1, MO2, M1
40.80 x 1.50 1./x 1.7/0.7  R  FG $12.0 000000   4661b Minarelli 2nd oversize for V1L lower
40.80 x 2.0/1.0 x 1.65/.6  L  G I  N/A   000000   4661a Minarelli 2nd oversize for V1L upper

40.80 x 2.00 1./x 1.7/0.7  R  FG $10.0  00  308.030.00 Garelli 4th oversize

41.00 x 1.20 1./x 1.7/0.7  R  G I  
N/A     
13010.GJ5.015 Honda TG50 Gyro, NN50 Gyro
41.00 x 1.50 1./x 1.7/0.7  R  FG  N/A    0 00000  00000 Minarelli V1 Industriale

41.00 x 1.5/1.3 x 1.80/7   T  G I $14.0 12140-16B10 Suzuki FY50, FZ50, FA50
41.60 x 1.50 1./x 1.7/0.7  R  G I $12.0 00 0000  00000 Minarelli V1 Industriale 3rd o.s
42.00 x 1.50 1./x 1.7/0.7  R  FG  N/A    0 00000  00000 Minarelli V1 Carabela 60cc
42.00 x 1.50 1./x 1.7/0.7  R  flat
$40/set    E660-00-50 Indian 4-stroke ring set comp(2) oil(1)
42.25 x 1.50 1./x 1.7/0.7  R  flat
$40/set    E660-10-50 Indian 4-stroke 1st o.s set comp(2) oil(1)
42.50 x 1.50 1./x 1.7/0.7  R  flat  N/A     
     E660-20-50 Indian 4-stroke 2nd o.s set comp(2) oil(1)

 

 


2. Piston Ring Information

Pinned or Not Pinned: Most moped piston rings are two-stroke style, where there are pins in the ring grooves of the piston that keep the rings from rotating around. Two stroke cylinders have holes or ports that the ring ends can snag on. So two stroke rings are pinned to the piston. Four stroke cylinders do not have any holes, so four stroke rings are not pinned. Knowing about those pins is important when installing.    

Getting the right rings: If your model is not in the applications, then you must measure the bore and the ring thickness. A calipers is the best tool to measure the bore (ring diameter) and ring thickness. Sometimes your rings might not be original, for many reasons. The piston might be aftermarket with thinner rings. The cylinder might be bored out to an oversize bore. Some mopeds came with more than one piston size or ring style.

Break a ring, how not to: Two stroke pistons have little pins (stumps, bumps) in the piston ring grooves that prevent the rings from rotating. Knowing where each ring locating pin is, and aligning the ring gap over the pin during cylinder installation, is the key to not breaking the ring. 

Measuring wear: A new piston ring is a the best tool to measure how worn a cylinder is. Conversely, a new cylinder is the best tool to measure how worn a ring is. To measure the wear of a ring, you need a perfectly round cylinder of a precisely known bore. A worn cylinder that has not been honed will still have it’s original new bore at the very top, above where the rings rub at. A new ring in a new cylinder should have a very small end gap of .004 to .008″. A worn but still OK cylinder with a new ring will have a gap of .0010 to .018″. A worn cylinder and ring both will have an end gap of over .020″(.5mm). A badly worn cylinder and/or ring will have a huge gap, over .030″(.75mm). You measure ring gap with a feeler gauge.

Classifying Jawa Rings

Classifying Piston Rings

Classifying rings: Rings get mixed up and are difficult to tell the size, unless a perfectly round cylinder of an appropriate size is available to place the ring in. If you try to squeeze a piston ring into a circle with just fingers, it inevitably becomes a very rounded polygon, or at best an ellipse. So the measurement becomes inaccurate. At right is how Myrons Mopeds’s Jawa piston rings were classified, using a piece of aluminum tubing with a tight fitting piston inside it to hold the tube round, and the test ring square. From top to bottom, 39.03 x 2.0, 39.28 x 2.0, 39.53 x 2.0, 39.78 x 2.0mm. Each ring increases in diameter by 0.25mm, so the circumference increases by Pi times that, or about 0.8mm. Here the inside of an old fishing pole tube is 39.78mm, perfect for the 3rd oversize 39.78 ring, on the bottom, with a gap of almost zero. Each gap is 0.8mm more because each ring is 0.25mm less diameter. It is important that the piston and ring fit the cylinder properly.   

Filing down: To make a ring slightly smaller, one of the two ring ends can be filed down, while preserving the shape. To reduce the size (diameter) by 0.20 mm, the end must be filed down by pi times that, 0.63 mm. When a filed down ring is installed in a cylinder smaller than it was designed for, two things change. The tension is greater, and the shape is slightly non-circular. So filed rings need a longer break-in period, to wear down the higher places. With 38 to 41 mm rings, the size can be reduced by 0.2mm with about 30 minutes of break-in, and by 0.5mm with about 2 hours of break-in. After break-in the rings have a mirror polish all around.

Why is the width not specified? Because the inner side of the ring does not touch anything. The ring has spring tension pushing it outwards, keeping the bottom (inner) surface from touching the bottom of the ring groove. So the ring width can be any amount, from about half the groove depth, to the groove depth. The exact ring width is not important. Exact ring height and diameter are important. 

 

 


3. Pistons


50cc pistons for sale here are listed by “pin”, the wrist pin thickness, and “upper”, the distance from the pin edge to the top edge. Pin ranges from 10 to 14mm. Upper ranges from 13 to 23mm.

Pistons in the same section have the same upper and pin dimensions, and so can potentially interchange, if the bore and maybe other things are the same. That is why pistons are listed by size rather than name.

For example, an oversize Peugeot 103 piston 40.5mm is perfect for a worn 40.4mm Morini MO1, after honing. They are both 12 pin and 16 upper, in the 12-16 section.

Alphabetical Name Index of Section Numbers
12-18
Batavus with Laura M48 engine
12-17 Benelli 1965-1980
12-23 Casal K177, others
10-19 Columbia with Solo 255 engine
12-22 Columbia with Sachs 505 engine

12-18 Daelim DP50, DK50 engine
12-22 Demm Smily

12-17 Derbi Variant, TT, RD50 1974-1986
12-18 Derbi Variant Sport 1986-90
14-24 Flandria Bermuda
12-18 Garelli Eureka, Noi, Gulp, VIP
12-22 Garelli Monza GT

12-16 Hero Majestic mid-90’s
10-20 Honda NC50, NA50, NU50, PA50
12-19 Honda NS50F
13-13 Indian AMI50 with PC50K1 re-make engine
14-18 Jawa Babetta 207 1970-83
12-16 Kawasaki AR50

12-20 Kinetic TFR with Piaggio re-make engine
12-19 Kreidler MP9, MP19
12-18 Laura M48, M56 engine

12-21 Minarelli V1L, V1HL engine
12-22 Minarelli V1, V1H engine
12-16 Morini MO1, MO2, MO4, M1, M101 engine
12-22 Morini S5K, S5K2, S5R, S5T engine
13-15 Motobecane 40, 50 with AV7 engine
10-19 Odyssey with Solo 254, 255 engine

12-16 Peugeot 102, 103 series
10-18 Puch MS50, others 50’s-60’s
12-17 Puch Maxi, others 1969-86
12-15 Rizzato 119 engine on Califfo
12-22 Sachs 504, 505 engine
10-19 Solo 236, 237, 254, 255 engine
12-21 Suzuki FA50 Shuttle, FY50, FZ50
10-18 Tomos A3 engine 1974-91
12-17 Tomos A35 engine 1992-2006 (cyl says A5)
12-17 Tomos A55 engine 2002-18 (case says A52)

12-18 Trac 1981-96 with M56-remake engine
10-19 TYM M48-remake engine on Angel, Speed Bird
12-20 Vespa (Piaggio) Ciao, Bravo, Grande, Si
10-21 Vespa (Piaggio) Ciao, Si (1990’s Euro)
10-20 Yamaha QT50 Yamahopper, PW50

 

Notes:
Piston actual diameter is measured at skirt (bottom), where it is largest. 
All new pistons come with new rings, clips and pin, unless noted.

Abbreviations:  “size” = cylinder bore                
gap FG foro grano means side pin gap style (aka GN grano normal)                        
gap GI  grano interno means center pin gap style  (see photos above)            
ring 1.5-3G
means trapezoidal (slanted) ring 1.5 x 1.3mm, GI gap style
ring 1.2-0F means trapezoidal (slanted) ring 1.2 x 1.0mm, FG gap style
ring Dykes means “L” type upper ring

 


10-18  1974-91 Tomos A3, 50’s-60’s Puch and Tomos

000000  part#   lower  @skirt   ring1    ring2   maker  price    38.0 bore, 10 pin, 18 upper
0000002074??    24.0  37.94  2.0FG   2.0FG  Mahle    none  original  Tomos A3 1.0hp (55 total height, 52 at edge)
000000207407   21.0  37.94  2.0FG   2.0FG  Mahle    none  original  Tomos A3 1.5hp (52 total height, 49 at edge)
000000207403   19.0  37.94  2.0FG   2.0FG  Mahle    $50   original  Tomos A3 2.0hp (50 total height, 47 at edge)
000000207403a 19.0  37.95  1.5FG   1.5FG  generic  $60   re-make Tomos A3
000000206200   18.0  37.9x  2.0FG   2.0FG  generic  none  re-make Tomos A3
000000  part#   lower  @skirt   ring1    ring2   maker  price    38.5 bore, 10 pin, 18 upper
000000202420   19.0  38.45  2.0FG   2.0FG  Mahle    none  original  Tomos A3 oversize

Tomos A3 piston

Tomos A3

18mm upper, 10 pin, 1950s-60's Puch

50’s-60’s Puch

Solo Piston

Tomos and Solo

Angel and Batavus pistons

Angel and Batavus

 
 
 
 
 
 

 

 


10-19  1976-80 Solo on Odyssey,Columbia, ’77-84 TYM Angel 

000000  part#   lower  @skirt   ring1   ring2   maker  price    38.0 bore, 10 pin, 19 upper
0000002200593  22.0  37.9x  1.5FG  1.5FG  Mahle    none  original  Solo piston “N”
0000002200600  22.0  37.9x  1.5FG  1.5FG  Mahle    none  original  Solo piston “U”
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 10 pin, 19 upper
0000000000000  15.0  39.92  1.5FG  1.5FG  generic  none  original  Angel/Speed Bird

A Batavus piston (12 x 33 mm pin) can substitute for an Angel piston (10 x 33 pin), if the piston pin needle bearing is changed. The 10x14x13 needle bearing (with 2mm rollers) needs to be 12x14x13. But there are none that thin (1mm rollers). So a bronze bushing 12x14x13 must be used instead of a needle bearing, like one from a Puch.  There are already oil holes in the Angel rod. Those holes need to extend through the bronze bushing to oil the pin.


10-20 1977-83 Honda NC50 PA50, Yamaha QT50 PW50

000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 10 pin, 20 upper
13101.147.000    18.0  39.95  1.5-3F 1.5FG  Honda   none  original  Honda NC50 and PA50 (has decomp cut)
13101.147.000a  18.0  39.9x  1.5-3F 1.5-3F generic  none  re-make Honda NC50, PA50 (after cutting decomp)
3L5.11630.00.00 17.5  39.9x  1.5-3F 1.5FG  Yamaha none  original  Yamaha QT50 Yamahopper and PW50

20mm upper (10mm pin) Honda NC50

Honda NC50, PA50

Honda NC50 and PA50 piston new

Honda NC50

20mm upper (10mm pin) Yamaha QT50 & PW50

Yamaha QT50, PW50

21mm upper, 10 pin, Vespa Euro models

Vespa Euro

21mm upper, 10mm pin Chinese scooters

Eton scooter

 

 

 

 

 

 


10-21  1990’s Vespa (Euro), China scooters

000000  part#   lower  @skirt   ring1   ring2   maker  price    38.2 bore, 10 pin, 21 upper
000000000000   17.0  38.13  1.5FG   1.5FG  Meteor   $60   original  Vespa Ciao & Si, 90’s Euro models
000000000000   17.0  38.1x  Dykes  1.5FG  generic   none  original  Vespa Ciao & Si, 90’s Euro models
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 10 pin, 21 upper
000000632964   18.0  39.9x  1.2-0F 1.2-0F  generic  $60   re-make E-Ton 50cc 2-stroke scooter
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.25 bore, 10 pin, 21 upper
000000632965   18.0  40.1x  1.2-0F 1.2-0F  generic  $60   re-make oversize for E-Ton 50cc 2-stroke scooter

 

Rizzato

12-15  Rizzato 119 engine on Califfo, Atala


00  part#   lower  @skirt   ring1   ring2   maker  price    39.4 bore, 12 pin, 15 upper
000
000000   23.0  39.32  2.5FG  2.5FG  generic  none  original  Rizzato Califfo (no rings)
00  part#   lower  @skirt   ring1   ring2   maker  price    39.8 bore, 12 pin, 15 upper
000
000000   23.0  39.72  2.5FG  2.5FG  generic  none  original  1os Rizzato Califfo (no rings)

This is an unusual design from the 1950’s, with the highest wrist pin. That allows transfer flow through the lower part of the piston, instead of around the sides completely. The top crown of the piston is a normal shallow dome, but with three equal large “bites” taken out of it. More about the little extraterrestrial later…


12-16  Peugeot 103 102, Morini MO1 MO2 M1 M101, 90’s Hero

000000  part#   lower  @skirt   ring1   ring2   maker  price    39.0 bore, 12 pin, 16 upper
00013001.1074   18.0  38.95  1.2-0F 1.2-0F generic   none original  Kawasaki AR50
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 12 pin, 16 upper
000000069707   17.0  39.88  2.5GI   2.5GI  Peugeot  $90   original  Peugeot Sort A
000000069708   17.0  39.89  2.5GI   2.5GI  Peugeot  none  original  Peugeot Sort B
000000069709   17.0  39.90  2.5GI   2.5GI  Peugeot  none  original  Peugeot Sort C (=AA)
000000069710   17.0  39.91  2.5GI   2.5GI  Peugeot  none  original  Peugeot Sort D (=BB)
000000000000   17.0  39.92  1.5GI   1.5GI  Asso 00  none  original  Verona (like MO1), 3mm skirt cut
000000000000   17.0  39.9x  2.0FG  2.0FG  generic   none  original  Hero Pacer, Panther
000000069711   17.0  39.92  2.5GI   2.5GI  Peugeot  none  original  Peugeot Sort E (=CC)
000000069712   17.0  39.93  2.5GI   2.5GI  Peugeot  $75   original  Peugeot Sort F (=DD)
00000MF553-F   17.0  39.93  1.5GI   1.5GI  generic   $70   re-make MMI for Peugeot
000000069713   17.0  39.94  2.5GI   2.5GI  Peugeot  $75   original  Peugeot Sort G (=EE)
000000069714   17.0  39.95  2.5GI   2.5GI  Peugeot  $75   original  Peugeot Sort H (=FF)
00000MF553-C   17.0  39.95  1.5GI   1.5GI  generic   $70   re-make MMI for Peugeot
000000069715   17.0  39.96  2.5GI   2.5GI  Peugeot  none  original  Peugeot Sort I (=GG)
00000069715a   17.0  39.97  2.5GI   2.5GI  Peugeot  none  original  Peugeot Sort HH
00000069715b   17.0  39.98  2.5GI   2.5GI  Peugeot  none  original  Peugeot Sort II
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.4 bore, 12 pin, 16 upper
000000000000   17.0  40.33  Dykes  1.5GI  Asso       none  original  Morini MO4, 3mm sk. cut ASSO 1929MO4
00000023.0125  17.0  40.31  1.5GI   1.5GI  generic   none  original  Morini MO1,2, 3mm skirt cut  says nothing
00000023.0125  17.0  40.32  1.5GI   1.5GI  Asso       none  original  Morini MO1,2, 3mm skirt cut ASSO.W 2352
00000023.0134  17.0  40.32  1.5GI   1.5GI  Asso       none  original  Morini M1, zero skirt cut,   ASSO W 1929M1
00000023.0125  17.0  40.32  1.5GI   1.5GI  Asso       none  original  Morini MO1,2, 3mm skirt cut   ASSO 1929
00000023.0125  17.0  40.35  1.5GI   1.5GI  Asso       $70   original  Morini MO1,2, 5mm skirt cut ASSO.W 2351
00000023.0136  17.0  40.3x  1.5GI   1.5GI  Asso       none  original  Morini M101 variator engine
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.5 bore, 12 pin, 16 upper
000000069716   17.0  40.44  2.5GI   2.5GI  Peugeot  $65   original  1os Peugeot oversize Sort K
000000069717   17.0  40.45  2.5GI   2.5GI  Peugeot  $65   original  1os Peugeot oversize Sort L
000000069718   17.0  40.46  2.5GI   2.5GI  Peugeot  $65   original  1os Peugeot oversize Sort M
000000069719   17.0  40.47  2.5GI   2.5GI  Peugeot  $65   original  1os Peugeot oversize Sort N
000000069720   17.0  40.48  2.5GI   2.5GI  Peugeot  $65   original  1os Peugeot oversize Sort P
000000069721   17.0  40.49  2.5GI   2.5GI  Peugeot  $65   original  1os Peugeot oversize Sort Q
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.6 bore, 12 pin, 16 upper
000023.0126/6   17.0  40.53  1.5GI   1.5GI  Asso      $75   original  1os Mor MO1,2, 3mm skirt cut ASSO 1929
000023.0135/6   17.0  40.5x  1.5GI   1.5GI  Asso      none  original  1os Mor M1, zero skirt cut ASSO W 1929M1
000023.0136/6   17.0  40.5x  1.5GI   1.5GI  Asso      none  original  1os Morini M101 variator engine
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.8 bore, 12 pin, 16 upper
000023.0126/8   17.0  40.72  1.5GI   1.5GI  Asso      $80   original  2os Mor MO1,2, 3mm skirt cut ASSO 1929
000023.0135/8   17.0  40.7x  1.5GI   1.5GI  Asso      none  original  2os Mor M1, zero skirt cut ASSO W 1929M1
000023.0136/8   17.0  40.7x  1.5GI   1.5GI  Asso      none  original  2os Morini M101 variator engine
000000  part#   lower  @skirt   ring1   ring2   maker  price    41.0 bore, 12 pin, 16 upper
000023.0126/0   17.0  40.90  1.5GI   1.5GI  generic  $80  original  3os Mor MO1,2, 3mm skirt cut  says nothing

16mm upper, 12 pin, Peugeot

Peugeot 103

16mm upper height pistons Peugeot left and Morini right

Peugeot and Morini

Morini Pistons Nov 2013

.

 

 

 

 

16mm upper, 12mm pin, Morini piston #230136

Morini M101

1995 Hero Panther

1995 Hero Panther

 

 

 

 

 

 

Morini made a variety of 50cc engines. These pistons shown here are only for 1960’s to 80’s moped-type engines Morini MO, MO1, MO2, M1, MO2 foot shift, MO4, all 40.4mm. They also fit Verona, early Gyromat, and Benelli mopeds, originally 40.0mm, as an oversize. All of the rings and ring pin locations are the same.

Peugeot 1980 tiny

Peugeot 103 pistons have slightly different sizes.

Peugeot 103 pistons have slightly different sizes, aka “sorts”.
Left of the red line are the “standard” 40.0mm sorts A to II (39.88-39.98).
Right of the red line are the “oversize” 40.5mm sorts K to Q (40.45-40.50).
Upper half are chrome bore cylinders, pre-1979 with single letter sorts A to Q.
Lower half are nikasil bore cylinders, 1979-on with double letter sorts AA to II.

Peugeot 103 moped pistons are a very old design that has been in use at least since the 1950’s. The rings are thick, 2.5mm, like most old rings were. Peugeot 103 cylinders are all aluminum with a chrome plated (pre-1979) or nikasil plated (1979-on) cylinder wall. They expand along with the aluminum piston as they get hotter. Unlike a steel sleeve cylinder that fits slightly loose, when cold, and wiggles a tiny bit, these should be a light sliding fit, where the piston, without rings, pushes through by hand but does not fall through by it’s own weight. When the piston fit is too loose, it makes a tinkle sound when idling, and produces less torque. When it’s too tight, it simply won’t move easy, or at all, and when hot it will smear (melt off) the hot exhaust side and stick (seize). The procedure for “fitting” a Peugeot piston requires a flat stone cylinder hone (not a ball hone) for first making the cylinder wall flat by removing any high spots, and a Dremmel high speed rotary cutting tool for removing burrs from the edges of the ports, and a small round file for removing burrs and high spots from the piston, especially around the wrist pin holes. Sometimes just the act of pushing the wrist pin in and out will raise the corner edge and make the piston fit tighter. The bare piston is pushed into the cylinder in different ways. The high spots are located, by feel and sometimes vision, and removed. When all high spots are removed, and the piston still does not fall through under it’s own weight, then the fit is perfect.  Worn cylinders need slightly bigger pistons. So a worn “C” cylinder might need a D, E, or F piston. Badly worn or “gouged” cylinders need to be replaced (unless the gouges are lower than the exhaust port). Peugeot has made plenty of “oversize” (40.5mm instead of 40.0mm) pistons. But there are no 40.5 cylinders in California, only 40.0mm. That’s why Myrons Mopeds has 40.5 pistons but no cylinders. Too bad it’s expensive to bore out and re-plate a nikasil cylinder. It is an option, made possible by the half millimeter bigger pistons available.

 


12-17  1969-86 Puch, 91-18 Tomos, 74-86 Derbi, 65-80 Benelli

000000  part#   lower  @skirt   ring1   ring2   maker  price    36.5 bore, 12 pin, 17 upper
000000229803    18.0  36.43  1.5FG  1.5FG  Vertex  $55   original  Tomos MC36 36cc kids dirt bike
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.0 bore, 12 pin, 17 upper
000000406300    19.0  37.91  2.0FG  2.0FG  generic $30   re-make Puch early 2000’s, way too small
000000406300    18.0  37.93  2.0FG  2.0FG  generic $40   re-make Puch Step II, made small to fit all
0000000037A-C  23.0  37.94  2.0FG  2.0FG   GOL     $60   re-make Puch, made in Italy by GOL
0000000037A-D  23.0  37.95  2.0FG  2.0FG   GOL     $60   re-make Puch,  made in Italy by GOL
000000the real 1 20.0  37.96  1.5FG  1.5FG  generic $55   re-make Puch,  made in Taiwan
000000233709    20.6  37.95  1.5-3F 1.5-3F Vertex  none  original  Tomos A55 alu cyl, pre-07 with trap. rings
000000233709    20.6  37.95  1.5FG  1.5FG  Vertex  none  original  Tomos A55 alu cyl = 37.98 07-09 14140 37.98
000000409000    18.0  37.95  1.5FG  1.5FG  generic none  re-make Tomos A35
000000223747    18.0  37.95  1.5FG  1.5FG  Vertex  $70   original  Tomos A35 std, has windows on in side
0000.802.5090    23.0  37.95  Dykes  1.5FG  Mahle  none  original  Derbi 1976-86     says 1003 E 119 A ?
0000001?????      20.5  37.95  2.0FG   none  Mahle  $75   original  Puch ’84 alu 37.99 sort C  says 38 C 1734
349.110.0069/21 20.5  37.95  2.0FG  2.0FG  Mahle  none  original  Puch alu cyl 37.98 sort 1   says 38 1 1019
349.110.0069/22 20.5  37.96  2.0FG  2.0FG  Mahle  none  original  Puch alu cyl 37.99 sort 2   says 38 2 1019
349.110.0069/23 20.5  37.97  2.0FG  2.0FG  Mahle  none  original  Puch alu cyl 38.00 sort 3   says 38 3 1019
349.110.0069/24 20.5  37.98  2.0FG  2.0FG  Mahle  $65   original  Puch alu cyl 38.01 sort 4   says 38 4 1019
349.110.0069/25 20.5  37.99  2.0FG  2.0FG  Mahle  $75   original  Puch alu cyl 38.02 sort 5   says 38 5 1019
350.310.0069/03 22.0  37.95  2.0FG  2.0FG  Mahle  none  original  Puch HT cyl 38.00 sort 11 says 38 1 1116
350.310.0069/04 22.0  37.96  2.0FG  2.0FG  Mahle  none  original  Puch HT cyl 38.01 sort 22 says 38 2 1116
349.210.5069/11 23.0  37.95  Dykes  2.0FG  Mahle  none  original  Puch HT cyl 38.00 sort 11 says 38.0 11 1593a
349.210.5069/22 23.0  37.96  Dykes  2.0FG  Mahle  none  original  Puch HT cyl 38.01 sort 22 says 38.0 22 1593a
349.210.5069/33 23.0  37.97  Dykes  2.0FG  Mahle  $65   original  Puch HT cyl 38.02 sort 33 says 38.0 33 1593a
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.2 bore, 12 pin, 17 upper
0000.802.5091    20.0  38.14  Dykes  1.5FG  Mahle  $65   original  1os Derbi 1os 1976-86 says 1003 E 120 B 0.25
0000.802.5091    20.0  38.15  Dykes  1.5FG  Mahle  $65   original  1os Derbi 1os 1976-86 says 1002 E 030
0000.802.5091    20.0  38.16  Dykes  1.5FG  Mahle  $70   original  1os Derbi 1os 1976-86 says 1003 E 120 A 0.25
0000.802.5091    20.0  38.15  Dykes  Dykes  Mahle  $65   original  1os Derbi 1os 1976-86 says Mahle 10 0.25
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.25 bore, 12 pin, 17 upper
349.310.4669/03 23.0  38.19  Dykes  2.0FG  Mahle  $75   original  1os Puch HT cyl 11 says 38.25 11 1593a
349.310.4669/04 23.0  38.20  Dykes  2.0FG  Mahle  $75   original  1os Puch HT cyl 22 says 38.25 22 1593a
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.4 bore, 12 pin, 17 upper
0000.802.5092     20.0  38.3?  Dykes  1.5FG  Mahle  none  original  2os for Derbi 1976-1986
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.5 bore, 12 pin, 17 upper
000000227334    20.5  38.4x  1.5FG  1.5FG  Vertex  none  original  1os Tomos A35
000000409001    20.x  38.4x  1.5FG  1.5FG  generic $60   re-make 1os Tomos A35
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.7 bore, 12 pin, 17 upper
0000.802.5093     20.0  38.6x  Dykes  1.5FG  Mahle  none  original  3os Derbi 1976-1986
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.9 bore, 12 pin, 17 upper
0000.802.5094     20.0  38.8x  Dykes  1.5FG  Mahle  none  original  4os Derbi 1976-1986
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 12 pin, 17 upper
00 70.06.04.00    18.0  39.9x  1.5FG  1.5FG  Asso     none  original  Benelli 1965-80 (old# G7346)
00 70.06.04.00a  18.0  39.95  1.5FG  1.5FG  GOL     $65   re-make Benelli 1965-80
000000000000    19.0  39.94  1.5-3F 1.5-3F Yamaha $60   original  Yamaha model?  complete
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.2 bore, 12 pin, 17 upper
00 70.06.04.02    18.0  40.1x  1.5FG  1.5FG  Asso     none  original  1os Benelli 1965-80 (old# G7346/2)
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.25 bore, 12 pin, 17 upper
000000000000    19.0  40.22  1.5-3F 1.5-3F Yamaha $30   original  1os Yamaha model?  without rings
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.4 bore, 12 pin, 17 upper
00 70.06.04.04    18.0  40.3x  1.5FG  1.5FG  Asso     none  original  2os Benelli 1965-80 (old# G7346/4)

17mm upper (12 pin) Puch

Puch

17mm upper (12 pin) Derbi Variant pre-'87

Derbi pre-’87

17mm upper, 12mm pin, Tomos A35 1992-06

Tomos A35

17mm upper, 12 pin, Benelli

Benelli

 

 

 

 

 

 
 

12-18  86-89 Derbi, 70-90 Garelli, 72-80 Batavus, 81-89 Trac

000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 12 pin, 18 upper
0F0.250.0091/A   19.0  39.945 1.5GI  1.5GI  Mahle   none  original  Derbi 1986-1989 flat reed eng, Sort A
0F0.250.0091/B   19.0  39.95  1.5GI  1.5GI  Mahle   none  original  Derbi 1986-1989 flat reed eng, Sort B
0F0.250.0091/C   19.0  39.955 1.5GI  1.5GI  Mahle   none  original  Derbi 1986-1989 flat reed eng, Sort C
0F0.250.0091/D   19.0  39.96  1.5GI  1.5GI  Mahle   none  original  Derbi 1986-1989 flat reed eng, Sort D
0F0.250.0091/E   19.0  39.965 1.5GI  1.5GI  Mahle   none  original  Derbi 1986-1989 flat reed eng, Sort E
0000000408211  14.0  39.92  1.5FG  1.5FG  generic $70   re-make Daelim (Trac) aftermarket (rect. rings)
0000000408201  16.0  39.92  2.0FG  2.0FG  generic $60   re-make Garelli/Batavus aftermarket
000000 0??????   14.0  39.9x  1.5-3F 1.5-3F generic none  original  Daelim (Trac) original (trap. rings)
0000000480580  14.0  39.95  1.5FG  1.5FG  Mahle   none  original  Batavus M48 original says 39.95
0000000080016  14.0  39.9x  1.5FG  1.5FG  Mahle   none  original  Batavus/Trac M56 original Sort A
0000000080017  14.0  39.9x  1.5FG  1.5FG  Mahle   none  original  Batavus/Trac M56 original Sort B
0000000080018  14.0  39.98  1.5FG  1.5FG  Mahle   none  original  Batavus/Trac M56 original Sort C
0000000080019  14.0  39.9x  1.5FG  1.5FG  Mahle   none  original  Batavus/Trac M56 original Sort D
0000000080020  14.0  40.0x  1.5FG  1.5FG  Mahle   none  original  Batavus/Trac M56 original Sort E
0000000 ??????   14.0  40.0x  1.5FG  1.5FG  Mahle   none  original  Batavus/Trac M56 original Sort F
00205058.2.150  xx.x   39.9x  2.0FG  2.0FG  Asso    none  original  flat top, Garelli alum cylinder 20, 25mph
00205088.2.150  xx.x   39.9x  2.0FG  2.0FG  Asso    none  original  flat top, Garelli alum. cylinder  30mph
00200001.2.150  16.0  39.9x  2.0FG  2.0FG  Asso    none  original  Garelli iron cylinder 20,30mph
00205053.2.150  17.0  39.9x  2.0FG  2.0FG  Asso    none  original  Garelli iron cylinder 25mph
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.2 bore, 12 pin, 18 upper
00200001.2.151  16.0  40.1x  2.0FG  2.0FG  Asso    none  original  1os Garelli iron cylinder 20, 30mph
00205053.2.151  17.0  40.1x  2.0FG  2.0FG  Asso    none  original  1os Garelli iron cylinder 25mph
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.25 bore, 12 pin, 18 upper
0000000480581  14.0  40.20  1.5FG  1.5FG  Mahle   $75   original  1os Batavus with Laura M48 engine
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.40 bore, 12 pin, 18 upper
00200001.2.152  16.0  40.3x  2.0FG  2.0FG  Asso    none  original  2os Garelli iron cylinder 20, 30mph
00205053.2.152  17.0  40.3x  2.0FG  2.0FG  Asso    none  original  2os Garelli iron cylinder 25mph
0000000534404  17.0  40.33  2.0FG  2.0FG  GOL     $55   re-make 2os Garelli (made in Italy)
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.60 bore, 12 pin, 18 upper
00200001.2.153  16.0  40.5x  2.0FG  2.0FG  Asso    none  original  3os Garelli iron cylinder 20, 30mph
00205053.2.153  17.0  40.5x  2.0FG  2.0FG  Asso    none  original  3os Garelli iron cylinder 25mph
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.80 bore, 12 pin, 18 upper
00200001.2.154  16.0  40.7x  2.0FG  2.0FG  Asso    none  original  4os Garelli iron cylinder 20, 30mph
00205053.2.154  17.0  40.7x  2.0FG  2.0FG  Asso    none  original  4os Garelli iron cylinder 25mph

18mm upper, 12 pin Daelim (Trac)

Daelim (Trac)

Batavus

18mm upper, 12 pin, Garelli

Garelli

Garelli piston markings

 

 

 

 

 

 

Asso

Garelli 4th oversize 40.8mm piston, made by Asso, says “40.8”. You can see it’s bigger. Middle, Garelli standard 40.0mm piston, made by Asso, says “40” and “S”. The “S” means scoria, Italian for exhaust. Right, Garelli standard 40.0mm piston, aftermarket. All three are oriented with the exhaust side down, like in the engine.

 

Kreidler

12-19  1970’s Kreidler Flory, 1990 Honda NS50

000000  part#   lower  @skirt   ring1   ring2   maker  price    39.0 bore, 12 pin, 19 upper
13101-GE2-305    16.0  38.94  1.2-0F  1.2FG  generic none  Honda NS50 1990, std
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.25 bore, 12 pin, 19 upper
13102-GE2-305    16.0  39.19  1.2-0F  1.2FG  generic none  Honda NS50 1990, 1os
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.5 bore, 12 pin, 19 upper
13103-GE2-305    16.0  39.44  1.2-0F  1.2FG  generic none  Honda NS50 1990, 2os
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.75 bore, 12 pin, 19 upper
13104-GE2-305    16.0  39.69  1.2-0F  1.2FG  generic none  Honda NS50 1990, 3os
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 12 pin, 19 upper
00002150383d     15.2  39.93  1.5GI  1.5GI    Mahle   $80   Kreidler Flory alu cyl 39.98 sort D  says R021 40154+
00002150383f      15.2  39.96  1.5GI  1.5GI    Mahle   none  Kreidler Flory alu cyl 39.99 sort F  says R021 40154+
00002150383h     15.2  39.97  1.5GI  1.5GI    Mahle   $80   (good used)    alu cyl 40.00 sort H  says R021 40154+
00002150383m    15.2  39.98  1.5GI  1.5GI    Mahle   $80   Kreidler Flory alu cyl 40.01 sort M says R021 40154+

 
 

12-20  Vespa (Piaggio), 1995-05 Kinetic TFR

  part#   lower  @skirt   ring1   ring2   maker  price    38.2 bore, 12 pin, 20 upper
182591    16.0  38.12  2.0FG  2.0FG  Piaggio   $60   original  std Vespa US ’78-80 Ciao Bravo Grande says USA
191034    16.0  38.1x  Dykes  1.5FG  Piaggio  none  original  std Vespa US ’79-86 Si, ’80-86 Ciao Bravo Grande
  part#   lower  @skirt   ring1   ring2   maker  price    38.4 bore, 12 pin, 20 upper
Kinetic     16.0  38.30  1.5-3F 1.5-3F  generic  none  original  std Kinetic    ’95-05 (Vespa remake) no arrow
112979    16.0  38.3x  2.0FG  2.0FG  Piaggio  none  original  std Vespa  all ’67-76 Ciao & Boxer, new# is 132521
132521    16.0  38.32  2.0FG  2.0FG  Piaggio  $50   original  std Vespa US ’76-78 Ciao, ’77-78 Bravo
182592    16.0  38.32  Dykes  1.5FG  Piaggio  $75   original  1os Vespa US ’78-86 Ciao Bravo Grande Si says 1M
  part#   lower  @skirt   ring1   ring2   maker  price    38.6 bore, 12 pin, 20 upper
152381    16.0  38.54  2.0FG  2.0FG  Piaggio  none  original  1os Vespa  all ’67-76 Ciao & Boxer, new# is 137681
137681    16.0  38.54  Dykes  2.0FG  Piaggio  none  original  1os Vespa US ’76-78 Ciao, ’77-78 Bravo    says 1M
182593    16.0  38.5x  Dykes  1.5FG  Piaggio  none  original  2os Vespa US ’78-86 Ciao Bravo Grande Si says 2M
  part#   lower  @skirt   ring1   ring2   maker  price    38.8 bore, 12 pin, 20 upper
152382    16.0  38.7x  2.0FG  2.0FG  Piaggio  none  original  2os Vespa  all ’67-76 Ciao & Boxer, new# is 137682

137682    16.0  38.74  Dykes  1.5FG  Piaggio  $65   original  2os Vespa US ’76-78 Ciao, ’77-78 Bravo   says 2M
  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 12 pin, 20 upper
633992    17.0  39.9x 1.2-0F 1.2-0F  generic  $60   re-make China 49cc two-strokes

20mm upper, 12mm pin, Vespa

20-12 x 38.4 Vespa

20mm upper, 12 pin, Vespa L-ring

20-12 x 38.2 Vespa

20mm upper, 12 pin, China two stroke

20-12 x 40 China

Vespa moped “USA” piston and cylinder

 

 

 

 

 

 

 

 

Ch-ch-changes: Vespa standard pistons changed in 1978 and 1980. Bikes made during those years can have either the older or the newer piston. There is no way to tell by ID numbers.

1978 bore reduction: In 1978 on US models the bore was reduced from 38.4 to 38.2mm. Some ’78’s have a 38.4 bore, and some have a 38.2 bore. Same thing happened to Minarelli at that same time (a reduction from 38.8 to 38.7). The pistons changed because of legal requirements.

1979-80 Dykes upper ring: In 1979 and 1980 the upper piston ring changed to L shape known as Dykes. Some ’79’s have regular top rings, and some have Dykes. Oversize Piaggio pistons already had Dykes upper rings since about 1977. This ring style was also adopted by Derbi in the mid-70’s and Puch in the late 70’s. It was mainstream in 1979! But by the mid-1980’s L-rings became out of style and obsolete. They did cost more to make, and broke easier. There was not much benefit. So all 90’s and later two-stroke moped engines have rectangular or trapezoidal top rings, mostly thinner than older designs.  

SC means exhaust (scoria): All original pistons are made by Piaggio and say Piaggio or have the logo on the inner side. They all have an arrow on top with the letters “SC”. That means “scoria”, Italian for “exhaust”. During installation, the arrow points toward the exhaust. Vespa pistons have skirt cut-outs rotated 30 deg.

Ring gap: Piaggio specifies the ring gap to be 0.1 to 0.25 mm (0.004 to 0.010″)

10 or 12mm piston pins: All of the Vespa moped pistons below have 12mm wrist pins. There are some (as yet unknown) non-US models with 10mm wrist pins.

Piston versions: By having all of the Piaggio Parts Manuals, and especially the Parts Amendments 1, 2, 3 etc, it was possible to extract all of the Vespa (Piaggio) moped piston and ring part numbers. The millimeter sizes are not in any parts manual. They are from service manuals and actual parts new and used.

1974-76 Ciao
1967-76 Ciao (Euro)
1970-76 Boxer (Euro)
1976-78 Ciao
1977-78 Bravo
1978-80 Ciao
1978-80 Bravo
1978-79 Grande
1979-86+ Si
1980-86 Grande
1980-86+ Ciao, Bravo
piston std
upper ring
lower ring
112979
38.4 x 2.0 FG 77775
38.4 x 2.0 FG 77775
132521
38.4 x 2.0 FG 77775
38.4 x 2.0 FG 77775
182591 (says USA)
38.2 x 2.0 FG 166945
38.2 x 2.0 FG 166945
191034
38.2 x L-ring 182519
38.2 x 1.5 FG 182518
piston 1os
upper ring
lower ring
152381
38.6 x 2.0 FG 98196
38.6 x 2.0 FG 98196
137681
38.6 x L-ring 137690
38.6 x 1.5 FG 137693
182592 (most say 1M)
38.4 x L -ring G.68473
38.4 x 1.5 FG 132515
182592
38.4 x L-ring G.68473
38.4 x 1.5 FG 132515
piston 2os
upper ring
lower ring
152382
38.8 x 2.0 FG 98197
38.8 x 2.0 FG 98197
137682 (says 2M)
38.8 x L-ring 137691
38.8 x 1.5 FG 137694
182593
38.6 x L-ring 137690
38.6 x 1.5 FG 137693
182593
38.6 x L-ring 137690
38.6 x 1.5 FG 137693

 


12-21  Minarelli V1L V1HL V1HLE, Suzuki FA50 FS50 FZ50

0000000000  part#   lower  x = 2, 3, or 4
000000
  part#   lower  @skirt   ring1   ring2   maker  price    40.3 bore, 12 pin, 21.5 upper

00000004541      15.0  40.2x   Dykes  1.5FG  Minn.   none  original  Minarelli V1L case reed, all-iron cylinder
00000004543      15.0  40.2x   1.5FG  1.5FG  Minn.   none  original  Minarelli V1HL case reed, sleeved al. cyl.
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.6 bore, 12 pin, 21.5 upper
00000004551      15.0  40.5x   Dykes  1.5FG  Minn.   none  original  1os Minarelli V1L
00000004553      15.0  40.5x   1.5FG  1.5FG  Minn.   none  original  1os Minarelli V1HL, V1HLE
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.8 bore, 12 pin, 21.5 upper
00000004561      15.0  40.7x   Dykes  1.5FG  Minn.   none  original  2os Minarelli V1L
00000004563      15.0  40.7x   1.5FG  1.5FG  Minn.   none  original  2os Minarelli V1HL, V1HLE
000000  part#   lower  @skirt   ring1   ring2   maker  price    41.0 bore, 12 pin, 21 upper
0012110.43000   15.0  40.92  1.5-3G 1.3-3G Suzuki  none  original  Suzuki FA50, FS50, FZ50
000000  part#   lower  @skirt   ring1   ring2   maker  price    41.5 bore, 12 pin, 21 upper
12100.35611.050 15.0 41.4x  1.5-3G 1.3-3G Suzuki  none  original  1os Suzuki FA50, FS50, FZ50
000000  part#   lower  @skirt   ring1   ring2   maker  price    42.0 bore, 12 pin, 21 upper
12100.35611.100 15.0 41.9x  1.5-3G 1.3-3G Suzuki  none  original  2os Suzuki FA50, FS50, FZ50

21mm upper, 12 pin, Suzuki FA50

12 pin, 21 upper, Suzuki FA50

 

 

 

 

 

 

 

 


12-22  Minarelli V1, V1H, Sachs 504, 505, Morini S5

000000  part#   lower  @skirt   ring1   ring2   maker  price    38.0 bore, 12 pin, 22 upper
000000406500 .   13.5  37.95  1.5FG  2.0FG generic $55   re-make Sachs 504,505 1C,1D  says 38
00286-378-051    14.0  37.95  1.5FG  2.0FG  Mahle  none  original  Sachs 504,505 1C,1D  553
00286-378-005    16.0  37.96  2.0FG  2.0FG  Mahle  $75   original  Sachs 504,505 1A,1B  552 says 37.98 G8
0000PC0922D      16.0  37.96  2.0FG  2.0FG  Meteor $60   re-make Sachs 504,505 1A,1B  Italian made
0000023-0101     16.0  37.93  2.0FG  2.0FG  Asso    none  original  Morini S5K, S5K2         says Asso 771
71.0455.0  4500  15.0  37.93  2.5FG  2.5FG  Asso    $75   original  Minarelli V1 1hp 20mph says Asso 825
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.2 bore, 12 pin, 22 upper
71.0455.7  4510  16.0  38.1x  2.5FG  2.5FG  Asso    none  original  1os Minarelli V1 1hp 20mph
0000023-0102     17.0  38.1x  2.0FG  2.0FG  Asso    none  original  1os Morini S5K2, can use Minarelli #4510?
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.4 bore, 12 pin, 22 upper
71.0455.7  4520  16.0  38.3x  2.5FG  2.5FG  Asso    none  original  2os Minarelli V1 1hp 20mph
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.6 bore, 12 pin, 22 upper
71.0455.7  4530  16.0  38.5x  2.5FG  2.5FG  Asso    none  original  3os Minarelli V1 1hp 20mph
00286-378-006    16.0  38.55  2.0FG  2.0FG  Mahle  $60   original  1os Sachs 504,505 1A,1B
00286-378-052    14.0  38.55  1.5FG  2.0FG  Mahle  none  original  1os Sachs 504,505 1C,1D
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.7 bore, 12 pin, 22 upper
71.0406.0  4535  16.0  38.62  1.5FG  1.5FG  Minn.   none  original  Minarelli V1 ’78-on-USA
000000  part#   lower  @skirt   ring1   ring2   maker  price    38.8 bore, 12 pin, 22 upper
000004540HP      15.5  38.73  Dykes  2.0FG  Asso    $75   original  Demm Smily piston, fits Minarelli
71.0410.0  4540  16.0  38.72  1.5FG  1.5FG  Minn.   $75   original  Minarelli V1 pre-’79-USA, P4 w/iron cyl
0000000034        16.0  38.72  1.5FG  1.5FG  GOL     $60   re-make Minarelli V1
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.0 bore, 12 pin, 22 upper
71.0460.7  4550  16.0  38.92  1.5FG  1.5FG  Minn.   $75   original  1os Minarelli V1
000023-0133A     16.0  38.98  1.5FG  1.5FG  Asso    none  original  Morini S5R, S5T (alum cyl 1sp kick)
000023-0133B     16.0  38.97  1.5FG  1.5FG  Asso    none  original  Morini S5R, S5T (alum cyl 1sp kick)
000023-0133C     16.0  38.96  1.5FG  1.5FG  Asso    none  original  Morini S5R, S5T (alum cyl 1sp kick)
000023-0133D     16.0  38.95  1.5FG  1.5FG  Asso    none  original  Morini S5R, S5T (alum cyl 1sp kick)
000023-0133E     16.0  38.94  1.5FG  1.5FG  Asso    none  original  Morini S5R, S5T (alum cyl 1sp kick)
000023-0133F     16.0  38.93  1.5FG  1.5FG  Asso    none  original  Morini S5R, S5T (alum cyl 1sp kick)
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.2 bore, 12 pin, 22 upper
71.0460.7  4560  16.0  39.12  1.5FG  1.5FG  Minn.   none  original  2os Minarelli V1
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.4 bore, 12 pin, 22 upper
71.0460.7  4570  16.0  39.32  1.5FG  1.5FG  Minn.   $75   original  3os Minarelli V1

0000000000        16.0  39.3x  1.5FG  1.5FG  Minn.   none  original  Harley Davidson M50 std
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.6 bore, 12 pin, 22 upper

71.0460.7  4580  16.0  39.52  1.5FG  1.5FG  Minn.   none  original  4os Minarelli V1

000000  part#   lower  @skirt   ring1   ring2   maker  price    39.8 bore, 12 pin, 22 upper

71.0460.7  4590  16.0  39.7x  1.5FG  1.5FG  Minn.   none  original  5os Minarelli V1
000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 12 pin, 22 upper

0208703.2.150   16.0  39.9x  1.5FG  1.5FG  Asso?   none  original  Garelli Monza GT, has port window(s), flat top
000000  part#   lower  @skirt   ring1   ring2   maker  price    45.4 bore, 12 pin, 22 upper

71.0485.7 0000  18.0  45.33  1.5FG  1.5FG  Minn.   $70   original  Minarelli big bore new in box
000000  part#   lower  @skirt   ring1   ring2   maker  price    46.0 bore, 12 pin, 22 upper
0000023-0140     17.0  45.93  Dykes  1.5GI  Asso    $70   original  Morini S5T big bore 68cc
0000023-0140     14.5  45.93  Dykes  1.5GI  Asso    $70   original  Morini S5T big bore 68cc, says AW 2665
000000  part#   lower  @skirt   ring1   ring2   maker  price    47.? bore, 12 pin, 22 upper

0000023-01??     14.5  47.00  Dykes  1.5GI  Asso    $70   original  Morini new in box, says Asso W 2508

22mm upper, 12mm pin, Morini S5E piston 23-0133 D

12-22 x 39 Morini S5E

16mm pin-edge to crown-edge, 12 pin, Morini S5 series (1970's -2002)

12-22 x 39 Morini S5 series

22mm upper, 12 pin, Minarelli V1

Minarelli V1

22mm upper, 12 pin, Sachs 504/505

Sachs 504

 

 

 

 

 

 

Asso

Asso Pistons

ASSO Pistons

Asso Factory

ASSO Factory

 

 

ASSO pistons were made in Italy mostly for Italian mopeds. ASSO stands for Assoluta Sicurezza Sempre Ovunque (Absolute Security Any time Anywhere). Early pistons said only “ASSO”, while later 1980’s ones said “ASSO.W”. Somehow ASSO merged with or was acquired by a German name, maybe some “kolben werke” to become ASSO Werke.

 


12-23 Casal

Mahle

000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 12 pin, 23 upper
0000000Casal    16.0  39.95  2.0FG  2.0FG  Mahle  $70  Casal, Zundapp?, bottom is flat

Casal 40mm piston top

Casal Ø40 piston top says
<–saida       Mahle E logo
D,E,F are size increments
for Mahle nikasil cylinder

Casal 40mm piston bottom

Casal Ø40 piston bottom
says “Mahle            401”
made by Mahle for Casal

Casal Ø48 Piston top

Casal Ø48 Piston top
C,D,E are size increments

Casal Ø48 piston bottom

Casal Ø48 piston bottom
says “Mahle            481”

 

 

 

 

 

 

 

 

Casal (made in Portugal) pistons are made in Germany by Mahle. They say “saida” on top, exhaust side, Portuguese for “outlet”. They have an unusual flat bottom. They have a total height of 50mm. Top edge to pin is 23mm, plus pin 12mm, plus pin to bottom edge 15mm. There are two bore choices 40 and 48mm, each with several 0.01mm (micro!) increments to get a precise fit. A cylinder of letter “F” should get a matching “F” piston, unless it is worn, then maybe a “G” or even an “H” would be best. If the piston fit is too loose the engine will be weak, noisy, and fussy. Too tight and it will seize and do damage. Piston rings are both size 40 x 2.0 FG gap style, like Garelli. 

 


Indian 4-stroke

13-13 Indian 78-84 AMI-50, 75-77 Honda PC50K1

000000  part#   lower  @skirt   ring1   ring2   maker  price    42.0 bore, 13 pin, 13.5 upper
bare E650-00-50 13.5  41.96 1.2flat 1.2flat generic none  original  Indian AMI50, Hon PC50K1
complete 6131 0 13.5  41.96 1.2flat 1.2flat generic $70   re-make Indian AMI50, Hon PC50K1

000000  part#   lower  @skirt   ring1   ring2   maker  price    42.25 bore, 13 pin, 13.5 upper
bare E650-10-50 13.5  42.21 1.2flat 1.2flat generic $45   original  1os In AMI50, Hon PC50K1
complete 6132 0 13.5  42.21 1.2flat 1.2flat generic $70   re-make 1os In AMI50, Hon PC50K1

 


13-15 Motobecane 1977-80 40, 50, 50V Mobylette

000000  part#   lower  @skirt   ring1   ring2   maker  price    39.0 bore, 13 pin, 15.5 upper
00000022273a    21.5  38.91  2.0GI  2.0GI   MBK      $60   Motobecane alu cyl 

00000022273      21.5  38.92  2.0GI  2.0GI   MBK      $60   Motobecane alu cyl 38.95 sort 2
00000022274      21.5  38.93  2.0GI  2.0GI   MBK      none  Motobecane alu cyl 38.96 sort AA
00000022275      21.5  38.94  2.0GI  2.0GI   MBK      none  Motobecane alu cyl 38.97 sort A
00000022276      21.5  38.95  2.0GI  2.0GI   MBK      none  Motobecane alu cyl 38.98 sort C
00000022277      21.5  38.96  2.0GI  2.0GI   MBK      $65   Motobecane alu cyl 38.99 sort E
00000022278      21.5  38.97  2.0GI  2.0GI   MBK      $65   Motobecane alu cyl 39.00 sort G
00000022279      21.5  38.98  2.0GI  2.0GI   MBK      none  Motobecane alu cyl 39.01 sort J
00000022280      21.5  38.99  2.0GI  2.0GI   MBK      none  Motobecane alu cyl 39.02 sort L
00000022281      21.5  39.00  2.0GI  2.0GI   MBK      $65   Motobecane alu cyl 39.03 sort N
00000022435      21.5  39.01  2.0GI  2.0GI   MBK      $65   Motobecane alu cyl 39.04 sort P  says P
00000022435a    21.5  39.11  2.0GI  2.0GI   MBK      $65   1os Motobecane alu cyl

 


Jawa USA

14-18 Jawa Babetta 207 series

000000  part#   lower  @skirt   ring1   ring2   maker  price    39.0 bore, 14 pin, 18 upper
0000281218a       15.0  38.94  Dykes  none  Meteor  none  re-make Jawa 210?  2 x 1 L-ring groove

000000
  part#   lower  @skirt   ring1   ring2   maker  price    39.03 bore, 14 pin, 18 upper

0000281218A      15.0  38.97  2.0GI  2.0GI    Jawa    none  original  Jawa 207, no pin or clips, says A Y
0000281218B      15.0  38.98  2.0GI  2.0GI    Jawa    none  original  Jawa 207, no pin or clips, says B Y
0000281218C      15.0  38.99  2.0GI  2.0GI    Jawa    none  original  Jawa 207, no pin or clips, says C Y
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.28 bore, 14 pin, 18 upper
0000281218/1A   15.0  39.22  2.0GI  2.0GI    Jawa    none  original  1os Jawa, no pin or clips, says 1A Y
0000281218/1B   15.0  39.23  2.0GI  2.0GI    Jawa    $60   original  1os Jawa, no pin or clips, says 1B Y
0000281218/1C   15.0  39.24  2.0GI  2.0GI    Jawa    none  original  1os Jawa, no pin or clips, says 1C Y
000000  part#   lower  @skirt   ring1   ring2   maker  price    39.53 bore, 14 pin, 18 upper
0000281218/2A   15.0  39.47  2.0GI  2.0GI    Jawa    none  original  2os Jawa, no pin or clips, says 2A Y
0000281218/2B   15.0  39.48  2.0GI  2.0GI    Jawa    none  original  2os Jawa, no pin or clips, says 2B Y
0000281218/2C   15.0  39.49  2.0GI  2.0GI    Jawa    none  original  2os Jawa, no pin or clips, says 2C Y

000000  part#   lower  @skirt   ring1   ring2   maker  price    39.78 bore, 14 pin, 18 upper
0000281218/3A   15.0  39.72  2.0GI  2.0GI    Jawa    none  original  3os Jawa, no pin or clips, says 3A Y
0000281218/3B   15.0  39.73  2.0GI  2.0GI    Jawa    none  original  3os Jawa, no pin or clips, says 3B Y
0000281218/3C   15.0  39.74  2.0GI  2.0GI    Jawa    none  original  3os Jawa, no pin or clips, says 3C Y

000000  part#   lower  @skirt   ring1   ring2   maker  price    40.03 bore, 14 pin, 18 upper
0000281218/4A   15.0  39.97  2.0GI  2.0GI    Jawa    none  original  4os Jawa, no pin or clips, says 4A X
0000281218/4B   15.0  39.98  2.0GI  2.0GI    Jawa    $65   original  4os Jawa, no pin or clips, says 4B X
0000281218/4C   15.0  39.99  2.0GI  2.0GI    Jawa    none  original  4os Jawa, no pin or clips, says 4C X

Jawa has 3 sorts times 5 sizes

Jawa PistonsJawa pistons have 14mm piston pins, thicker than most other 50cc piston pins. There is not a good substitute for Jawa piston, not even one with a smaller pin. 

Markings: The marking on top tells the sort (A,B or C) and the size (std or 1,2,3,4).

 

 Size translation: The table says a “1B” piston is 39.21 mm, measured “34,5mm from the base” just below the lower ring. Four “1B” pistons actually measured 39.21 there, and 39.23 at the skirt. Other “1B” pistons were 39.20 and 39.22, 39.21 and 39.22, and 0.02 more at the skirt. Other samples were “B” (standard) 38.94 and 38.96, “2B” 39.44 and 39.46, “3B” 39.70 and 39.73, “4B” two at 39.95 and 39.97, all 0.02 wider at the skirt. Based on these eleven new pistons, all measured the same way at the same time, the Jawa piston sizes can be translated to standard piston sizes. Jawa piston sizes (measured at the lower ring) are, on average, 0.02 mm less than standard piston sizes (measured at the skirt).

Piston to cylinder clearance: From the Puch service manual the piston to cylinder clearance for a similar steel sleeved aluminum cylinder, is min 0.030, max 0.055 mm. From the Jawa table of piston sizes (at right), it says the new piston-to-cylinder clearance is min 0.065, max 0.075 mm. Subtracting 0.02 mm from this gives min 0.045, max 0.055, more in agreement with Puch. 

 


Flandria

14-24 Flandria Bermuda

000000  part#   lower  @skirt   ring1   ring2   maker  price    40.0 bore, 14 pin, 24 upper
000000000000     11.5  39.9x  1.5FG  1.5FG Flandria none  Flandria Bermuda 1977

This is unusual in many ways. The transfer flows through the piston instead of around it.
The wrist pin is lowered to allow more intake air flow. This upper length of 24 is the most for 50cc pistons. The wrist pin measures 13.98 x 33 mm.

 

4. Piston Information

It’s important that the piston fits the cylinder properly. An old messed up piston that fits correctly is better than a new piston that fits too loose or too tight. Too loose will be hard to start and weak. Too tight will seize up when hot. Often a cylinder needs to be bored out slightly to fit an oversize piston. Some aluminum cylinders have plated walls that cannot be bored out. The piston diameter, measured at the skirt, is a hair smaller than the cylinder bore.

The following piston/cylinder clearance limits are from the Puch factory service manual:

Puch “Lo-torque” nikasil plated aluminum (7-fin) cylinders:  Min .0008“(.020mm)   Max .0016“(.040mm)

Puch “Hi-torque” steel sleeved aluminum (8-fin) cylinders:  Min .001″  (.029mm)    Max .002“(.055mm)

 Puch  “Magnum” steel sleeved aluminum (9-fin) cylinders:  Min .001″  (.029mm)    Max .002“(.055mm)

As the engine gets hot, the piston to cylinder clearance approaches zero. Besides “diam“, “upper“, “pin“, and “lower“, other things matter in piston compatibility. The ring pins must locate the ring gaps so they never pass over a port. The exhaust-side skirt must be long enough to cover the exhaust port at tdc. The intake-side skirt, on a piston port two stroke, controls the intake timing. Shorter skirt opens sooner and closes later. A longer intake skirt is one way some mopeds are restricted in power. Simply grind the excessively long piston skirt back to 30mph specification, but no farther, to de-restrict the piston. Puch, Tomos, Garelli are the main kinds that use longer pistons to lower the speed, for 25 and 20mph states or jurisdictions.  This list contains all pistons made by original equipment manufacturers, although most of them are no longer available. The not-available ones are listed for their information, such as speed versions or piston size choices. If you happen to have an unknown piston with or without a part number, you can identify what it is from this list by measuring it and looking for matching measurements. From all these specifications, perhaps a compatible piston can be found or adapted.