heres whats up. i purchased this 2000 trailblazer 250 had maybe 8 hrs ride time on it and quit running. did compression check it was at 60 psi, so deciced a topend rebuild was due. sent the jug to local machine shop with rings and piston to make sure of proper clearance since i did bore 2 mm over to 74mm wiseco piston. bought new topend gasket kit and put back together. but instead of the compression getting better it went down to 30 psi which i do no understand. can any 1 give me any advice what might be wrong.

 

are you sure the piston ring was installed right if not that will cause compression loss may also do damage to cylinder wall

 

Did you ever check the piston to cylinder clearance after they bored the cylinder? Should have been no more than .002 clearance. Plus did you have the correct torque on the head bolts,also sure you may not have broken a ring or upside down as mentioned? Markings on the rings face up.Plus with this old of a model,crank seals may need to be replaced! OPT

 

the instructions said it did not matter how rings went on piston. and the machine shop checked all the clearances when they bored the cylinder so pretty sure the clearance is right. and can any 1 tell me what the torque specs on head bolts on 2000 polaris 250

 

What brand of piston was used?? Might be a stupid question: Did you install piston with with ring locating pin facing the intake?? Have had some people that didn't!! If you installed it correctly,still thinking about the ring?? Should have a mark as most rings other the dykes type rings have marks indicating top because the ring or rings are usually tapered! DON'T hold me to it,but I think the head nut torque is 18-20 foot pounds? I can remember the 500 by heart and its in several sequences!, and I should know the little 250! OPT

 

as far as i remember it does matter on which way the rings go. i would guess that the rings are the issue or at least that would make the most sense.

 

it is a 74mm wiseco piston that i used

 

It HAS marks on the rings!! could be the problem?? OPT