i'm working a friend's trx90 that has some engine problems. the motor would not spin through a complete cycle. i've pulled the head and cylinder. the piston seems to be siezed to the wristpin and/or connecting rod. do these not have wristpin bearings? any idea how to get wristpin out so i can replace the piston? thanks.

 

If that engine seized a rod/piston/wristpin, you will be replacing the crankshaft.
Im guessing it ran out of oil to have seized.
Will probably need to be bored also.

 

boring won't be a problem. the cylinder really isn't scarred that much. a good hone would clean it up nicely. as far as replacing the crankshaft, is there no way to get the pin out without ruining the rod? i could care less if i ruin the piston/wristpin at this point but didn't really want to have to tear into the bottom end. and as for it running out of oil, the owner didnt specify but i'm assuming the same thing. lol

 

Well Im guessing that the rod is already damaged. Does the wristpin still move freely in the rod? if not, the damage is done.
If it does, you can cut the piston with a hacksaw from the top down alongside the rod end.
If you have the luxury of air tools that you can use cutoff discs on that is much faster. You just have to keep cutting chunks of the piston away.

 

air tools/grinders are readily availble. do you think there is any chancethat after the piston has been cut away i can get the pin out of the rod and maybe polish the inside of the rod with emery cloth or something? have any other ideas or is the bottom end coming apart regardless?

 

I have done it before as a bandaid job, but it can be done.
Above all, dont try to drive the wrist pin out without some sort of support on the rod, you will bend it... then your screwed.
You didnt mention if the wrist pin is seized in the rod or not... thats a mitigating factor.

 

i think the wristpin is seized to both the piston and the wristpin. i got ahold of my local honda dealer and they said i could use a bolt that will slide through the pin but the head will not. put a washwer and nut on it and start tightening the nut and it will pull itself through. makes sense to me, i guess i'm going to try it. if you have any other suggestions, please let me know. thanks again.

 

Go to a site such as Dennis Kirk and have a look at a Wrist Pin Puller.
That will give you an idea of what you need to make one.... just the bolt and nut like you mentioned wont work... it need a "pipe" type object for the pin to be pulled into, otherwise the pin would just move to the washer you mention and stop.
Good Luck to you.

 

We have factory made & home made wrist pin pullers .. And to tell you the truth the home made one works better than the factory puller .. Once you get the wrist pin out I'd be suprised if the rod was useable
The clearances are:
Rod I.D. 13.016-13.034 mm ---service limit is 13.05 mm
Rod to piston pin clearance is 0.016-0.040 mm service limit is 0.07 mm

This is a couple of my wrist pin pullers..