2000 YZ 426 Engine Rattle

Has anyone experienced an unspecified rattle coming from inside the clutch case? Upon inspection, it was found that the main gear bolt, behind the clutch basket was loose, and that the main gear, and oil pump gear were very loose, and the shear pin on the main gear was almost sheared in half. The suspected cause is a bad day at yamaha. Anyone else ever run into this problem? New shear pin, tightening of the bolts, and some new clutch plates, and no more rattle.

Shear pin on the main gear?

Are you referring to the straight key that holds the counter balancer drive gear in place on the crank?

This is a very well-documented problem with some 2000 426s. Do a search on "key" or "straight key" or something similar, there are literally hundreds of posts on this problem...

...Yamaha either installed a mis-sized key or one made of an overly-soft material; or perhaps using a key to secure the balancer drive gear is just a bad idea, from '01 onward the gear is held w/ splines.

Hope this helps.

Thanks for the info in the "key". It holds the gear behind the clutch basket. Not only was it almost sheared in half, but the bolt on the gear was loose too! It is fixed and ready to go now.

Not only was it almost sheared in half, but the bolt on the gear was loose too! It is fixed and ready to go now.

When there is play in the key to keyway fit the to-and-from motion of the gear works the retaining nut loose, even though there is a lock-tab washer on that nut.

I would recommend you inspect everthing again after about 20 hours of use just to be on the safe side. I replaced my key w/ another Yamaha part and it came apart again (the next one I got from an automotive supply house, hardened 5 mm I think).

Worst case scenario is the lock-tab washer or main nut damages the oil passage in the cases and you lose oil pressure to the bottom end (that would be bad).

Just FYI.

Hick, when you say the bottom end, is the piston and small end of the rod part of the bottom end that is supplied with oil from these passages?

Hick, when you say the bottom end, is the piston and small end of the rod part of the bottom end that is supplied with oil from these passages?

The end of the crank fits inside an passage (w/ an O-Ring) inside the right cover. The first place oil is delivered to from the main pressure pump is to this passage which feeds the big end via the hollow crank.

I don't know if there are oil passages in the small end or not, I wanna say not but can't remember for certain...

...if it is directly oiled it is obviously going to come from the crank.

The rest of the pressure goes to the head and tranny via that big chrome manifold on the right side of the motor.

Hope this helps. :thumbsup:

Shear pin on the main gear?

Are you referring to the straight key that holds the counter balancer drive gear in place on the crank?

This is a very well-documented problem with some 2000 426s. Do a search on "key" or "straight key" or something similar, there are literally hundreds of posts on this problem...

...Yamaha either installed a mis-sized key or one made of an overly-soft material; or perhaps using a key to secure the balancer drive gear is just a bad idea, from '01 onward the gear is held w/ splines.

Hope this helps.

Tell me more about this key. I have a 2000. No symptoms and going on over a thousand hours. Is it possiable to fit the 01 parts in my bike to fix the potentily deadly part?

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