Just picked up a non-running Grizzly 350 to tinker with. Was told it 'Ran 4 months ago but won't crank now'. Short story is it wouldn't fire even on starting fluid and it has 30psi compression.. Clearly has a bigger problem than sitting.. I'm pretty good at stuff like carburetors and other external type engine work. I've done a few valve adjustments, but rarely dive into the internals. With compression that low would you assume a broken ring or some sort of a head issue? What should I check next or is it just time for a tear down?
2007 Yamaha Grizzly 350 low compression
- Thread starter nwjones18
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Do a wet compression test.
Just did it and compression doubled to 60psi on the wet test.. I don't have a way to hook air up to it, but I believe this tells me that I have bad rings/worn cylinder correct?
Yeah I'm thinking it must have been overheated or run without oil.. Anyway I could tell if the bottom end had serious issues without a full disassembly? It would be pretty painful to put a new top end on an engine I've never heard run just to have the bottom end knock.. All I know is the oil in it currently looks new and it sounds normal turning with the electric starter.
Can you pull a side cover and get to the flywheel? Then when the head comes off I think you can tell if the rod bearings are kaput by how much you can turn the flywheel before the piston moves.
If the cylinder is scored, it'll be coming off, and I think you might be able to gauge bearing wear since you can access the rod.
If the cylinder is scored, it'll be coming off, and I think you might be able to gauge bearing wear since you can access the rod.
No one mentioned spark. Are you getting spark at the spark plug? I like using a $5 spark plug tester but you can also remove the plug and ground it.
It is common with these utility bikes for people to suck water into them and break a piston ring or bend a rod. You've got a major issue at only 30PSI but a topend rebuild should have you on your way. get a service manual
Yes.
I'd check the valve adjustment before doing anything else - easy check. It's possible someone did it wrong (trying to do a "tune-up") and one of the valves is not fully closing. A tight valve could be from normal valve wear too (clearance gets smaller), and the valves have never been adjusted.
That's a good thought. I'll have access to that to set it to TDC for dissassembly so I can give the rod a good wiggle and check for up down play. I guess if that's good I'd roll the dice and put a new top end on it. The kits I'm seeing are only like $150 on amazon and have decent reviews.
https://www.amazon.com/gp/product/B...&pf_rd_p=edaba0ee-c2fe-4124-9f5d-b31d6b1bfbee
I didn't mention it originally but it has strong blue spark. I will check the valves before I dissassemble, but jsut looking at the covers/bolts there is no indication its been messed with. I'll definitely be investing in a service manual..
Sort of a gamble either way.. I already paid to much for it, now I have to rebuild and also fix things like brakes and tires.. Go ahead and sink some good money in after bad.. haha
Stuck the bore scope down the plug hole today.. Cylinder walls look rough, although I am not smart enough to look at it and guess if it might have been water intrusion or oil starvation..
might have been mud intrusion..I'd check the intake track out...but either way, a new piston/rings and cylinder bore are in order at a min.
If it was oil starvation you cam journals will be wiped as the cam rides directly on aluminium
Air cleaner could be wasted, or major intake leak letting dirt into the engine. Looks like major scoring. As suggested, look at other engine components for signs of lack of lubrication wear.
Thanks all I'll post some more pics when I get it apart.. I cleaned the carb before I checked compression and it wasn't full of mud or anything, but there were signs that the airbox had been full of mud at some point and 1/2 way cleaned out... Had a filthy k&n air filter on it.
I don't know this specific model, but the camshaft likely rides directly on the head casting. That's where oil starvation would show up first if that is what killed this engine.
Yes, when you remove the cam look at the saddles and cam caps, it will be readily apparent if there is scoring.
Got it apart today.. Thankfully head and connecting rod seem to be in good shape.. Going to put that cheap top end kit in it and see what happens. Looks like it got badly overheated to me.
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