Son was on his way home Friday and the motor locked while en route. No low oil warning light just shut down. Electric start wont turn her over and the pullstart is impossible to move.

Question is where should I begin? Was gonna pull the drain plug today and look for shavings first. Should I pull the motor from the ATV and start a tear dow and evaluate?

 

They don't have a low oil light. There is an oil temp light on most quads. Anyway, yes take the drain plug out to find out if there is any oil in there. Then take the head and cylinder off, you don't need to take the engine out for this. On most low oil seizures the gudgeon pin (wrist pin) seizes first, this causes piston seizure. Quads have roller bearing cranks so they tend to be OK, but check for play in big end by moving the con rod up and down. I often have to scrape the con rod eye to get a new gudgeon pin to fit, and if the bore is scored, it will need a re-bore and oversize piston. If the piston has broken up, you will have to strip the engine to get the bits out. Check cam and followers for wear, overhead cams don't like being short of oil either.

 

Drained the oil. Looks to be plenty of oil, and there were no shavings in the oil. It seems pretty darn clean

Guess the next step then is to pull the plastics and gas tank and see what the top end looks like.

 

I'm no mechanic but it seems a little odd that the engine would just lock up like that. Was it at least smoking before this happened, which would be a clear indication of engine wear. My friend had this happen to his Grizzly many years ago because he basically was riding it wide open for about 9-10 miles. Not something atv engines like. That will definitely cause damage. Knowing this, I seldom push my current Grizzly past 40-45 mph even though I know it will top 60 mph. Where I ride most of the time about 30 mph is top speed except in the few wide open spots where I might get to 40 if I want. There are plenty of tight trails where 20 mph is almost too fast.

 

How do you know its the engine locked an not transmission or clutch or brakes locked down in gear!!! just afew things to check before takedown...what does the spark plug look like? broke off? troasted? chalky white?Is engine mudding?

 

Once the engine has slowed enough for the clutch weights to back off, the engine is not attached to the transmission so would re-start "on the button" if the problem was further down the drive train. As the bike wasn't short of oil, any number of things may have caused a seizure, but the only way to find out is to open it up, and I would go for the top end first.

 

No smoke, just quit and locked up

Stay tuned folks.....time to get invasive

 

If it was a clutch problem, it would still start and run but just wouldn't go anywhere. I had the belt break on my Grizzly 660 a few months ago and it still started just fine but would only move if I put it in neutral. The 350 has basically the same cvt system.

 

Pretty sure it is not clutch related neither the electric start or pull start will budge

 

2008 Yamaha GRIZZLY 350 4WD (YFM35FGX) Clutch | Ronnie's Mail Order