show off your piston mods!

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young grease monkey

New Member
Sep 20, 2011
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Chicago
i want to mod my piston to alter the transfer port timing a little and the skirt on the intake. i know, one at a time. looking for some examples. i have a gt5 66cc with sbp pipe and filters.
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
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living the dream in southern california
i don't have any pics, but trimming the skirt is simple. just set your motor at TDC, then stick a Sharpie into the intake port and mark the chunk that covers the port.

take the head and the jug off and grind away on the piston. use a smooth file or something to make sure there's no burrs or harsh edges, then put it back together.

easy.
 

young grease monkey

New Member
Sep 20, 2011
362
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Chicago
how did it turn out? was the power noticable? and i'd also like to make better flow where the transfer ports touch the piston by grinding the piston a little. what do y'all think?
 

bairdco

a guy who makes cool bikes
Aug 18, 2009
6,537
264
63
living the dream in southern california
trimming the skirt is a great mod, in my experience. the most noticeable improvement is how the bike accellerates. it's much smoother.

as far as power goes, a smoother running engine has more power, but the top speed isn't increased by too much. you're basically just getting a better tuned engine.

as far as shaving the piston dome goes, that's a touchy situation. if you do it too much, you'll end up losing power. graham bell has a good report on that ( google "graham bell 2 stroke" to find it.)
 

young grease monkey

New Member
Sep 20, 2011
362
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Chicago
cool! i have time to do that now that i have to barrow a tap set to fix the rear mounting holes... damn thing spends half it's time broken. the bolts just broke as i was riding.
 

Easy Rider

Santa Cruz Scooter Works
Jan 15, 2008
2,145
7
38
Nor*Cal
I've seen alot of piston mods and every good goped engine builder (TS, Bartilone & Combee) used piston boost ports as well as extra transfers.
 

dmb

Active Member
Dec 4, 2010
1,354
3
36
lakewood ca
and at bdc the piston covers the transfer ports. pretty weird stuff if the air fuel charge is blocked. but the skirt mod puts more pressure in the bottom forcing more fuel air through the blocked ports, every little bit helps. i'd be nice if they were in the right place to begin with. cant cost any more to change hole location in the begining. sorry this is on HT china girl
 
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Greg58

Well-Known Member
May 1, 2011
5,353
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Newnan,Georgia
I did the skirt trimming on one of my bikes a couple of weeks ago after reading about it in the performance tips section and some advice from 2door. As was said the increase in power on mine was mostly low end, I gained about three mph up the road from my drive to the crest of the hill. If you think about it any amount you take off the skirt in affect doubles, it opens the port fully at tdc and opens the port sooner on the up stroke. I took around .250 off in the center of the piston so the way I see it the intake port is open alot more.