Seized 660cc motor : what happened ?

[Bill Jurgenson]

Yup!! More interesting even: 2 balancer shafts! which are different from each other. The new smaller one placed under the crank (vertical vibes) and the old behind the crank (horizontal vibes) This points to a lighter crankshaft. The back balancer is the same part as in the 660 engine. It is intended to counteract the tranversal vibes the big end and crank pin make at 90 and 270º and which the counter weight on the crank can't help much. the new addition counteracts the larger piston in the 700 so that they can lighten the crank a bit as well.

The question remains why the new XT660 engine does not use this bottom end? It uses the same head. Indeed, why they don't use the same engine, period?
Simple enuf to leave out the reverse gear.

[andrerav]

Hi!

I own a 1994 Yamaha XTZ 660 with 58 000 km on the speedo. The engine has never failed or had its key replaced or gears tightened.

I can hear a slight ticking noise when I rev the engine from idle. The ticking fades in, persists, and then fades out as the rpm increases. This happens in lowish rpm range, between 1000-2500 or so. The ticking is a bit louder when under load, but either way it is not really loud nor does it sound disturbing (yet).

It does *not* sound like valve ticking, and I have wondered what it might be. From what you guys are describing, the drive key could be the cause.

So I'm figuring I should get a new key + gasket (and possibly that Slipstream gear) and do the job this winter.

So I have four] questions:

* Where can I get that Slipstream gear? (:

* What is the part number of the key?

* Should I consider replacing the clutch while I'm at it?

* Is it possible to remove the balancer permanently without splitting the engine? Will this damage anything except the blood circulation in my hands over time?