01 YZ250F Balance shaft Gear Failure and general overhaul questions.

phranticness · Feb 11, 2007

Has anyone seen this failure? or a simular failure causing the same conditions?

I just picked up a 01 YZ250F, It's got some damage to the right side of the motor, It appears to me the small weight that bolts the balace shaft gear came off, as if the heads of the bolts sheared off. This in turn damaged the clutch basket, oil pump and 50% of the other gears on that side.

I'm going to go through the whole motor, but I'd like to isolate the cause, or at least be aware of possible commen failure points.

Also, are'nt the early YZF's prone to cam chain failure or stretch, regardless of appearance should it be replaced along with the tensioner?

Thanks.

BadgerMan · Feb 12, 2007

phranticness said:
Also, are'nt the early YZF's prone to cam chain failure or stretch, regardless of appearance should it be replaced along with the tensioner?

Actually, I think this applies to all model years, not just the early ones. The chains stretch quickly which can cause undue wear on the crank/sprocket and a possible timing related catastrophic failure if not replaced regularly. It is a twenty dollar item so replace it every time the top end is apart. I never needed to replace the tensioner in the six years I owned my 2001 YZ250F.

Sorry, but I have no experience with the counter balancer failure.

phranticness · Feb 12, 2007

thanks for the heads up.

phranticness · Feb 14, 2007

I've come to a new conclusion. I belive the reason the left side of the motor grenaded was a broken kick start shaft. I found out the previous owner replaced it only a week before the explosion, I suspect a broken piece of the shaft found it's way around the the balance shafts gear, broke the weight off and the domino effect began.

Ol'89r · Feb 15, 2007

phranticness said:
Has anyone seen this failure? or a simular failure causing the same conditions?
Thanks.

phranticness.

I had a YZ426 in the shop that did that very thing. As it turned out, the customer broke a tooth on fifth gear and continued to ride the bike. The tooth eventually found it's way into the counterbalance gear and shattered the gear.

He was out in the middle of the desert and continued to ride the bike until all of the bits and pieces gathered on the flywheel magnets and stopped the engine. By the time I got the engine, everything from the head gasket down was toast.

I believe your new conclusion is correct. That is most likely what happened and you will most likely find the broken piece of the shaft attached to the flywheel magnets.

Bummer. :(

01 YZ250F Balance shaft Gear Failure and general overhaul questions.

phranticness

BadgerMan

phranticness

phranticness

Ol'89r

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