97 Trail Blazer 250 has 30psi compression. I removed head and gasket looks ok with no carbon trails to outside. Cylinder wall is scored above exhaust port. Sisyphus2k2 said his lack of compression was the lower crankcase gasket. Any way to check that before a complete teardown? What other things to check before spending major time and dollars for rings and rebore? I'd hate to spend the money on rings & rebore, then find the compression leak was somewhere else.

 

PM Bubba297 and he can give you the answer about the crankcase gasket. While it is apart you would be wise to get the cylinder bored, wiseco piston and a trail port job. Then look into a pipe/clutch kit to wake it up.

 

Can you feel grooves with your fingernail, or does it just have an appearance? If it's grooved, it's time for a top end job. 30psi is very low. Even with a blown base gasket, top end compression would still be higher than that.Bubba

 

Bubba, the grooves above the exhaust port catch a fingernail, not just appearance. Hence, get the cylinder rebored, right? Any estimate of approx rebore cost? We used two different compression gauges and turned it over with the elec starter many times, and fast, still best was 30psi. I think I'll replace cylinder base gasket, head gasket, rebore cylinder and new rings (oversized to fit rebored cylinder). Anything else you think I might need? The ATV is driven by a 12-yr-old so no mods are wanted because he can get into enough trouble driving stock. Thanks!

 

I guess before I say anything else is : How did it happen that all of a sudden you have only 30psi of pressure? An engine will quit starting well above that mark.At least 80psi must be there to even crank up. You didnt have an oil related failure such as pump not adjusted correctly or maybe he ran the tank out of oil? That would be the #1 reason for a big failure, but most of the time they seize up.If all that is ok, redo the top end. It is extremely easy on the 250. You should be able to get it bored for around $50. Look on ebay for a piston kit under polaris. There is a guy who's ID is sledpartsguy that sells the weisco kit real cheap (usually about $60-$65. Other than that get a base gasket and a new head gasket and your ready to go.Attention to detail and a good break-in will yield excelllent results with a long life. Hope this helps,Bubba

 

usually when ya take the head off, and all looks fine and dandy cept for a few scrapes by the exhaust..

you take the jug off and find a cracked or broken piston skirt.

 

Thanks!! I'll take the cylinder off and see if there's a cracked piston skirt. Then search EBay for some parts. Bubba, this machine is ridden by a friend's kid, so it's possible he ran out of oil and didn't tell want to tell his dad. (When I was that age, I also thought I could cover up my mistakes.) But, I'll check the pump anyway.

 

Polaris Mech, thanks for the add on. I completely forgot to add the part about the factory slugs being a bomb waiting to go off. Knowing it was a young driver, could definitely be the culprit. Bubba[img]i/expressions/face-icon-small-happy.gif[/img]

 

I took the cylinder off and found the piston is trash. (Polaris Mech said so.)The exhaust side of the piston is severely grooved so that the rings are virtually welded into their grooves and don't protrude at all. Now I'm wondering if the cylinder can be rebored, since the grooves are pretty deep. It had to be a lot of heat and friction! It's a wonder it kept running and didn't seize, but the result would have been the same . . . mucho dinero. Thank you Bubba and Polaris Mech. Thanks again!

 

I pulled the reed cage out of my 350L to put in the RAD valve. I saw the skirt was cracked, so thats when I did my initial rebuild.

I heard that the reason polaris has the skirt problem is due to boring the cylinder while the sleeve is still cold from installing it. Has anyone else heard this? It makes sense. As the sleeve warms it gets larger to the point of being out of spec before the engine is even assembled.

I am looking for a mild port job for the 350. Where is the best place to go? I already have the hot seat pipe (I know it isn't the best but I am keeping it), 38mm carb, RAD valve, race gas head cut.