How much piston skirting to remove?

Denis Zen

Active Member
Mar 30, 2021
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Riding up highway 101 at sunset
I got the anbull 80 cc motor and when I removed the intake manifold I was surprised to see that at tdc there was like 5 mm of skirting showing. Is this normal or did anbull pre trim the piston?

I already get 45 mph out of my bike, I cant imagine gaining much more by trimming that much off.
 

Greg58

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May 1, 2011
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I take a sharpie and mark the piston inside the intake port at TDC, then remove the piston and die grind the skirt so the port is fully open, I did this to my Avatar 10 years ago, it really woke it up. Mine is a 48cc so it might not make that much difference.
 

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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I always recommend not touching the skirt...
Think about how the engine works; as the piston goes down, the intake port will close & the trapped fresh air/fuel charge will be forced to travel up the intake ports into the cylinder... If you raise the edge of the skirt, you'll be allowing more of the fresh intake charge to escape back out of the intake port (& not be forced up into the cylinder)!

Most people who do this mod will get a little more top end speed but will lose way too much bottom end power. :(

I know Greg had good results when he did his, but he's also experienced with these engines & knows how to alter the engine in many other ways to compensate for the modification.
 
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Greg58

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On my engine the piston skirt covered almost 1/3 of the intake port, I didn't remove anymore than what was needed. That's why I said that it might not make a difference in yours, if you are already getting 45 I wouldn't change a thing. I went from 20mph to 31+ after trimming, porting, jetting and the pipe.