The Thread Spread - Revisited
_______________________________________
-Balance Shafts-
Loose Gears Hurt Ears
- The Yamaha Blaster engine, like the Honda TRX engine and many others uses a gear driven weighted counter balancing shaft. The lash between its gears - the normal tolerance for straight cut gears meshing with each other - can cause a noise which under some conditions sounds like an engine knock. While the engine accelerates, the balance shaft is constantly trying to decelerate - hence the noise, when the engine decelerates the balance shaft has inertia to try to keep it going - more noise. Running under little or no load at any RPM will bring this sound out the most.
- Real engine knock (detonation) could immediately destroy a piston at high revs in a matter of seconds. The gear lash "slapping" noise associated with the counter balancer has made more than one Blaster, TRX or LT owner hand their quad over to a dealer for a rebuild. The rider with a careful ear can detect the difference between the two sounds and continue to ride safely knowing that everything is OK. The best way to know the difference is that if the noise is really loud and your engine is still running, its probably the balance shaft because if it were detonation you'd be pushing the quad by the time it got that loud. Detonation, the kind that destroys engines is rarely heard and if it is it is just before a meltdown. If you've heard real detonation at high revs, you've visited the dealer for new parts shortly thereafter.
- Rick
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