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Old July 22nd 05, 05:07 PM
Brian Stell
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> It is loudest on a cold engine, and in the afternoon, with engine still
> warm, is never that loud again. It also becomes very high in frequency when
> cold when the throttle is released, after driving in low gear and low load,
> the clatter increases just after release in volume and frequency, and
> diminishes after about a second ...


I can see valve noise being influenced by RPM
(more RPM => more noise) but I'm unfamiliar with
valve noise being influenced by throttle.

My experience with rod bearing noise is it is
loudest when accelerating / hill climing
(more engine power => more noise) and is quiet
when off throttle.

I've been told the main bearings tend to be
noisy all the time.

Now the "diminishes after about a second" makes
me think gear lash. As in something is spinning
and the normal resistance keeps the "front"
side of the teeth engaged. When going off throttle
the spinning item's inertia keeps it spinning so
the gear is bouncing between the "front" and
"rear" side of the teeth. When the engine speed
stops dropping it's back to resistance / "forward"
teeth. If the slowing is heavy then the inertia
can keep the "rear" side of the teeth engaged.

Driving down a grade, off throttle, at a constant
speed would create a similar force on the bearings
as off throttle but no inertia / spinning changes.

Do you get the noise under this condition?

Or only when the engine is dropping RPM?
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