Piston skirt touching casing......

[alanscottj]

Had to take top end off my GP this afternoon - gave everything a look over to check all is well and I have noticed a mark on the casing where the piston skirt has been hitting. It only appears to be hitting in one very small area and thankfully there doesn't appear to be any damage to the piston. This would explain the knocking noise that I have been unable to locate

I do have a dremel and can easily dremel the bit of the casing, but, the fillings will get into the casing and wreck my seals and bearings. Is it ok for me to shave a tiny bit off the bottom part of the piston skirt? as I can do this away from the engine and make sure no fillings get any where near the engine. The piston is very barely touching the case so it won't be a lot that I need to take off to remedy it.

Thoughts? Cheers

[holty]

hi scott,
i had the same problem with a polini evo kit i fitted to a smallframe vespa, as you suggest i filed a small part off the piston, i did both sides to keep it balanced,not a problem on case induction, if your trimming the skirt that goes into the inlet port you will increase your inlet timing, this will increase spitback and fuel consumption if you remove too much.

[alanscottj]

hi scott,
i had the same problem with a polini evo kit i fitted to a smallframe vespa, as you suggest i filed a small part off the piston, i did both sides to keep it balanced,not a problem on case induction, if your trimming the skirt that goes into the inlet port you will increase your inlet timing, this will increase spitback and fuel consumption if you remove too much.

Hi Holty, no the bit I need to trim is the bottom so the bit facing the exhaust port

[rosscla]

And if it's for the TS1 inlet timing isn't a consideration anyway.

[holty]

yes if its reedvalve then no problem, i would trim a little with a file, then draw your file along the edge so its not sharp, like you say easier than an engine strip, do you have a long stroke crank, or what piston are you using ?

[alanscottj]

Yes, on TS1.

It looks like it is just the corner edge of the bottom corner of the piston skirt that is touching, so I have just rounded off the corner ever so slightly. Put back together and using the flywheel to move piston in and out there is no touching at all. Hope this cures the old knocking noise