low RPM and pitting

[Bill Jurgenson]

After all the discussion of thumper or not and what supposedly modern engines are, here from the Dutch Monoforum showing just what I mean. The picture are from an SRX which, with its rediculously long final drive ration and 18" wheels is notrious for excessively fast gear wear. Being a memeber of taht forum, I don't know if non-members can simply go look, so I am linking the jpegs directly.
5th gear pitting as usual:


the "partner gear"


and here the 2nd gear:


both 2nd and 5th are particularly suseptible, 2nd because of the overly large step between 1st and 2nd in all but the SZR versions and 5th for what should be obvious reasons.

here is the link:
http://forum.monoconnection.nl/viewtopic.php?t=664&start=45

[DAVID THOMPSON]

as we say where i live "That looks like a mell of a hess"
ar dave

[Bill Jurgenson]

...

a mell of a hess.

here is another potential hell of a mess:



you can see that both the primary gear and that driving the balancer shaft were not tight. This is one of the best kept secrets at Yamaha concerning this engine group. It happens because the the package - the two gears plus the spacer and the two sheetmetal spring retainers for the balancer gear - is undersized and this primarily because the two sheetmetal discs get compressed. When the package is too small, the big nut on the crank locks up against the shoulder that can be seen. No amount of tightening then tightens the package and the 6mm woodruff key in the crank must bear the entire torque. Sooner or later it shears off and the balance and crank meet - just once - and the both are finished for good.

This happens much more frequently than Yamaha is wont to admit.
Keep and eye on this and on the gear on the balancer itself were similar stuff can happen.

[DAVID THOMPSON]

looks like that motor is toast unless you have a shed full of good spares...

we get the raptor motor over here in an ATV ...

some of the guys have nicknamed it the craptor because of problems
with it ....but they do run the h%$#l out of them

some of these guys could break anything with a rubber mallet.

ar dave

[Bill Jurgenson]

The pics are from the srx, the same as the Grizzly 600.
Bottom ends the same for all the engines following this design:xtz, srx, TT, SZR, Grizzly 600 and 660, and 5 valve Raptor.
The last 5 valve Raptor and the new 4 valve engine have a different crank.

Craptor?
I'd say that says a lot more about the drivers/owners than about the design...

[basser23]

Bill,
I would tend to agree about the owner/driver statement..a lot of these
folks will endlessly modify these motors to the ragged edge of reliability
and then wonder why they break.... just my 2 cents opiinion
Chip

[sokota]

Does the balance shaft scenario apply to a 96 660 scorpion ? Is a proper size washer under the nut to properly load the parts a cure ? Thanx for the heads up