engine knocking; here's what I found - Snowmobile Forum: Your #1 Snowmobile Forum

davidcat370 · 01-13-2008, 09:24 PM

Well ,finally pulled the engine (2001 A/C Z570 ESR with 1700 miles) due to a knock in the engine.
Here are the photos from the exhaust and carb sides, both of the flywheel side cylinder with scoring on the piston and cylinder wall.
Any ideas on possible cause.? bad piston wrist pin bearing ?I am assuming this will mean a bore, hone and oversize piston; need I do the other as well, it looks fine?
Something that can be tackled by a first timer ? Good with a wrench and mechanically inclined but I don't have any speciallty tools.
thanx
Dave

**smallengineguy** · 01-13-2008, 09:30 PM

Looks like it leaned out, either a crank seal leaked, cracked carb boot, etc. A good hone might clean the cylinder up.

Bulldog · 01-13-2008, 10:36 PM

Did you do anything to the jetting or was it old fuel?

davidcat370 · 01-13-2008, 11:09 PM

No, running new fuel and no carb work that I know off. There is some oil leaking from the head on that side of the engine......Haven't aken the shroud off yet to see what is causing it. Could a leak in the head gasket contribute to that ?

**smallengineguy** · 01-14-2008, 07:10 AM

Not usually, unless it's leaking antifreeze INTO the engine.

davidcat370 · 01-14-2008, 08:09 PM

not liquid cooled; this is on a 570 f/c.

Bulldog · 01-14-2008, 08:37 PM

If you still have the motor together check the crank seals. With the motor running spray some starting fluid or 2 stroke mix onto the PTO crank seal. if it revs the seal is bad. can do the same with carb boots. might have to pull hte clutch to do this

SnoCro · 01-14-2008, 09:03 PM

1700 miles is not many, Just wondering if it was bought new and if oil was added to the gas then drove easy during breakin? The oil leaking possibly could be from running too hot(warm days,idling to long)and Bad carb boots are one of the pistons worst enemy. Maybe the oil injector clogged or is not doing its job at high rpms. Well, a couple more things to look for. I would do the one.

fossil · 01-14-2008, 10:03 PM

You'd hope they last longer than that.
If you got it pulled I'd rip it apart and give it a good checkover. Just cost you seals and gaskets if all else is ok. Looks like the piston and cylinders are going to need attention though. I'd check the carbs and induction while your at it.

davidcat370 · 01-14-2008, 10:05 PM

bought it used but sure there was no knocking when I heard it run. It did seem a little boggy but I wrote that off to bad fuel......The compression checked out good on both cylinders at 125... Would the engine have an audible knock with just this piston scoring or am I also likely to find a bad bearing someplace???

SnoCro · 01-14-2008, 10:43 PM

Hopefully you won't have to split the case, Wrist pins, The pins needle bearings and the spacers do make it knock and are a weak link. Torerances be comes slop, usually caused from too much heat or too little oil. You will probably have to pull the jug to know for sure.