Wrist pin stuck, 66cc HT bicycle engine

maurtis

maurtis

New Member
Since I have my motor out of the bike to switch frames, I figured I would go ahead and trim the piston skirt and clean up the ports. I did not do that before initially mounting the motor since the cylinder did not want to separate from the crankcase and I did not want to push my luck with my first HT build.

So last night I pulled off the head and cylinder and the ports were surprisingly clean, so no work done there. Take the retaining pins out of their grooves, and use a large hex key to try to push the wrist pin out. It slides out about 1/2" and stops...

So I try pushing it out the other side, and it does not even clear the piston. So try some more to push it out the other side, and it slides out about 1/2" and stops. So without being able to get the wrist pin out to remove the piston, I chose not to try and trim the piston skirt while on the motor, so nothing done there either.

I saw posts about putting the engine in the oven to get the piston to expand a little, but I was not ready to go that far quite yet. Now if I ever need to take the piston off, say to replace the wrist pin bearing, things could get interesting.

Everything seemed to go back together fine. I made sure the piston rings had their openings over the locator pins (which were a lot smaller than I had thought they would be), put a good coat of 2 stroke oil on the piston and cylinder before reassembly and everything seemed to move smoothly and freely.

So the good news is that I did not trim anything, so theoretically the motor should run the same as it did before taking it apart. Hoping that my motor does not develop and new and exciting leaks when I get her running again! LOL
 
Re: Wrist pin stuck, 66cc HT

The common way to remove tight wrist pins is to use a short piece of pipe or tubing with an I.D. slightly larger than the wristpin against the piston, and an allthread rod with nuts and washers slightly smaller than the o.d. of the wristpin on the other side of the piston.
Tighten the nut on the tubing side to pull the wristpin out of the piston and into the tubing.
 
Re: Wrist pin stuck, 66cc HT

Great tip, I love it! Hopefully it will not come to that, but in the event that it does, very good to know of an easy solution. Thanks Wayne.
 
Re: Wrist pin stuck, 66cc HT

i just stick a bolt in there, and smack it out with a rubber mallet.
 
Re: Wrist pin stuck, 66cc HT

bairdco said:
i just stick a bolt in there, and smack it out with a rubber mallet.
Click to expand...

I was tempted to do exactly that, but was only two beers into it when I ran into the wrist pin issue and thought it was better to err on the side of caution. I should have waited until a couple of beers later...

Venice Motor Bikes said:
You can heat the piston & it will slide right out. ;)
Click to expand...

With a torch? I was reading some threads here last night about this while struggling with it and people said to NOT heat it with a torch. I guess for fear of igniting extra fuel?
 
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