M20 motor with a noise

[Dave Nichols <dave.nichols@xxxxxxxx>]

Yesterday at a lapping day my e30 had it's first motor problem at a driver's
school ( and it's been to dozens and had a multitude of drivers)

The car came off the track with a strange metallic "knocking" that was
intermittant.  We pulled the valve cover off and everything in the valve
train is normal and quiet.  The knocking sounds like it's coming from
underneath the intake in the middle of the engine.  We immediately thought
it was a rod, but's it not regular.  At idle everything is normal and quiet
with just the ticking of the injectors.  If you take the engine up to about
2000rpm, you hear a knocking, and when the throttle is released, it goes
away.

Not wanting to take any chances, we loaded the car on the trailer and took
it home.  When I cranked it to get it off the trailer, it was quiet and
normal.  Even slightly revving the motor failed to produce the knock.  As
the oil begain to heat up, the knocking slowly returned, but much fainter
and even more sporadic.

Questions:  Could this be an oil pump problem related to oil viscosity?
(pump weak and not able to maintain pressure under load with thin oil)

Does the sporadic nature of the knock mean anything?

We're going to pull the sump on Monday and check the pump and all the
bearings.  BTW, we pulled the plugs out of the circuit one at a time to kill
one cylinder at a time and it didn't make any difference.

Thanks.
Dave the WEENRDOG (e30 325eis?)
Dixie (1994 740il black and tan dachshund, built for comfort not for speed)
Heidi (1996 M3 light weight dachsie, quickest, best handling pooch on the
planet)

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