Have a 87 Lt80 bought not running.(100$ special) did a full rebuild (ebay/amazon parts, i know not great)but ran great for a few weeks then lost compression. replaced the jug, head and piston rings. still no compression. round 3 replaced head studs, nuts and head gasket with OEM parts. (fired right up and ran great for a day) went to start and back to less than 40lbs of compression. if i'm not mistaken everything above the rings to the spark plug should only affect compression. just trying to find a start point or anything at this point. If I need to go with a full PRO-X kit I will. also rebuilt the factory carb (works great) and replaced the reeds.

I can rebuild a 4 stroke all day long but this has stumped me. fully rebuilt a 93 warrior 350 and a 98 Yz400f and lots of other small motors. Any and all ideas would be great.

 

It's the Wuhan special. Their pistons are terrible! The studs stretch, etc.
Round 2: did you replace all that with OEM?
The Prox kit is just a piston kit. They don't make cylinders, nor does Wiseco. (same owners).
The Prox pistons are cheaper. I'll stick with OEM personally. You should too.
I have bored OEM cylinders here with all the goodies to do the top end. It will end your frustration.

 

I have oem studs installed (new) and nuts, have a oem head gasket waiting. Where can I buy your goodies? Need a bored cylinder, piston and rings. For reference how much compression should I be seeing?

 

90 minimum.
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