AV7 70CC parmakit troubles

Erik /

May 27, 2009 07:42PM

I finally finished port matching my case, installed new bearings and seals and tried to put it all back together only to hit a stumbling block. The wrist pin is way snug in the piston, to the point that the only way I could get it to slide in was to heat up the piston with a torch. Has anyone else had trouble getting the wrist pin to slide in? I'm considering just sanding the channel on the piston just enough to get the wrist pin to slide in without too much resistance. Unfortunately while the piston was hot, it fell and I broke a corner off the piston. Is it unusable now? I think it would still be OK since all it does is expose the smaller transfer on one side a little earlier. But please tell me if I'm wrong. I just don't want to mess up my kit by running a damaged piston.

The pics are of the damage after I filed the rough edges down a bit.

By funkwaffle at 2009-05-27

AV7 70CC parmakit troubles

Erik /

funkwaffle OP

May 27, 2009 07:44PM

Re: AV7 70CC parmakit troubles

Jesse Stephenson /

Go to branch

jesses

May 27, 2009 07:47PM

the piston is fine, but make sure the edge did not bulge out or otherwise distort. If it feels tight in the cylinder at that point then file or sand it down until it it feels good. But the edge being broken there is fine. If you reuse the stock needle bearings and crank they are sometimes very hard to press together. Good luck with it.

Re: AV7 70CC parmakit troubles

Andy /

akpasta

May 27, 2009 08:25PM

Erik,

That is pretty normal. Many pistons are designed this way, whereas, the stock moby engine has more of a "floating" wrist pin design. 103s on the other hand, are a total bitch in the same way you're talking. I've actually broken pistons trying to wedge the wrist pin in there.

You need to make a tool out of a c-clamp and an old belt or something to push the wrist pin on one side and hold the entire piston securely on the other. Heat helps, but most of all, drench the whole thing in 2-stroke oil or something.

And... DO NOT re-use the clips that go on either side of the piston, I learned that the hard way.