24,000 RPM

[Mike Arman <armanmik@n-jcenter.com>]

>From: Joan  Kotjarapoglus <jkot+@pitt.edu>
>Subject: tapping noise between 2400-3000rpm
>
>Wife  and I gave our 86  5000 cs non turbo to our dauther for her use.  We
>bought the car with 15k and it served us well.  It presently has about
>120k and has been kept after so that it still a pleasure to drive.  My onl
>y complaint is a tapping sound which started many many years ago.  It
>starts at approximately 24,000 rpm and stops at 30,000rpm, especially
>under load conditions.  If I stomp hard on the foot brake and  gas the
>engine until it hits the 24-30k range, it is loud as can be and it seems
>to come under the car (snip)

At 24,000 RPM, the noise you are hearing is the pistons and conrods exiting
the engine via the oil pan. At 30,000 RPM, the louder thump is the
crankshaft striking the ground on its way to China.

Damn, I had no idea a 5 KS would rev that high, or Darn, your daughter sure
does drive fast!!!!!!! (License plate "SNC-BOOM")

Seriously, though, it appears that you've done all the "usual" diagnostics
- you may get to look for some unusual ones.

Loose flywheel, perhaps? This almost sounds like a harmonic vibration
problem because it occurs in a narrowly defined RPM range. If you had a bad
rod bearing, it most likely would have failed by now. Anyone check the
contents of the oil filter? - cut it open and look for metal? Maybe an
aircraft-style oil analysis is in order - $25 fee sure beats the price of a
precautionary tear-down!

Best Regards,

Mike Arman