First time poster...please be kind! My son has a 1989 LT80 that we bought off of a friend a little over a year ago. I have changed the piston, rings, wrist pin, etc at twice since then. The second time I bought a Wiseco 51mm piston and replaced it, and had the cylinder professionally machined. Now, my son brought the quad home saying it shut off while he was riding. I thought it wasn't getting fuel and played with that for a while - cleaned out the carb and jets really well. Finally got a compression tester and compression was only reading 60-70psi. Piston looks good and cyliner seems allright as well, so I only replaced the rings (with Wiseco replacements). I figured I would compression test it before I put everything completly back together - basically just left the top of the jug off and the air tubes unhooked - and I still have poor compression. I am at my wits end with this. Would the jug and the filter tubes need hooked up to get proper compression, or I am I just having more and more problems? I am not intensely mechanically inclined, but have learned much from this forum and forums like these. I didn't think the rings would go so quickly, but he does run the crap out of it the entire summer. Any help would be greatly appreciated! Thanks in advance!

 

Maybe try a Suzuki piston and see if the tolerance is OK (.0025 to .008). The Wiseco demands a .003 and I make em .0035-.004
I don't like Wiseco's altho they usually work OK with a stock motor.

 

Hey LT80. Thanks for the reply...and I must say I am greatful for your reply...I've read a ton of your posts that helped me before!

If I try a Suzuki piston, I would have to go back to stock, correct? That would mean a new cylinder, head,etc. I went from 50 to 51mm when I replaced the piston with a Wiseco product. Like I said, everything "looks" good. Are there any other reasons bad compression could happen? I read that reeds might cause this as well. (I put Boyesen reeds in when I changed the piston.) The reason I ask is I hate putting a boatload into the quad because I am thinking my son might be able to step up to something bigger. I would still like to fix it though....

Whether this info is right or not, I was also told the head gasket is done and needs to be replaced once the head is taken off. Is this true? Thanks for the replies again, and I'll try to be quicker to post back next time!

 

Head gaskets are a 1 off use item. Put a small amount of oil in bore and see if compression improves. If so, then rings.
Also put an air lead from a compressor into the plug hole (via a seales adaptor). With a low pressure, listen to inlet & exhaust ports for valve leakage (If a 4 stroke)

 

I think you should take the cyl back to the shop that bored it and ask them to measure the piston to cyl clearance. Let's go from there before you go buy another piston.
Thr oil in the cyl (like mentioned above) helps but I doubt it'll raise your comp enough.
You can reuse the head gasket.
If the new piston is needed, no, you wouldn't need a new cylinder unless the bore is over 51mm.
Wouldn't need a new head for any bore.
And I don't think the reed is affecting the comp reading.