we own a sportsman 90 for the kids, it is a 2001. last year I replaced the jug, piston and rings and gaskets to tighten it back up since compression was down to 30 psi. now only a year later I'm back down to 30 psi. It doesn't look like the jug is scored, and I can't believe the rings would have worn out in only a years time. any guesses as to what may have caused this much wear and tear in such a short time? thanks in advance.

 

Has it been rode hard?Maybe a cracked cylinder,or damaged piston,or rings which is my guess.

 

my guess is that because the air filter on it is a crappy design. it is allowing dirt to get into engine

 

Our little 90 just done the same thing with only 40lbs of compression. Any advice on exactly what to replace would be great. We pulled the head and removed the parts. None looked real bad but with that low of compression it will need to be replaced. Thanks

 

If the cylinder doesn't look too scored or scratched up a hone job on the jug, new rings and gaskets should do it. maybe check the top of the piston out too for wear.
Since I just replaced the jug and piston last summer that's all I have to do this time. I was going to try to hone it myself but will probably take it to a small engine shop to get it done.
I think I have about 30 bucks into rings and gaskets so far. just need to find the time to get it done.