Checking for Cancer....was: RE: [Shotimes] Ticking/oil leak

[George Fourchy]

On Wed, 23 Apr 2003 23:35:39 -0700, Kerry Kinion wrote:

>And by the way - If it was crank cancer
>would it be heard thru the entire RPM range?  If a valve shim is out of
>spec would it be heard thru the entire RPM range?  Question is: why only
>between about 2400-3000 am I hearing this??

We can't answer the question why you are hearing the noise only between 2400-3000
rpm until we find what the problem is.  Have you tried running the engine with both
accessory belts off, to silence all the external accessory sound sources?  I did
that when diagnosing my engine, and it still made the sound with all accessories and
pulleys stopped.  All you have to do is start it, and run the revs up and down a
couple of times.  It won't hurt it to run it without the waterpump for a minute or
less, but make sure it is at least partway warmed up.

The classic crank cancer symptom is noise at idle to about 2500 rpm after the engine
warms up.  The noise comes from the loose crank sprocket slamming back and forth
against the key (and ringing the crank like a big bell) due to the tension on it
from the various cam lobes varying the effort required to turn the cams.  Above
about 2500 rpm, momentum of the cams evens out the load, and this fact combined with
the fact that at that speed and above there isn't time for the sprocket to bounce
back and forth stops the noise.  Until I took my engine down to find this looseness,
there was no way I could figure out why such a noise would be there, and why it
would be so loud and heavy.  The instant I saw the gear and key, I understood.  With
the miles, I thought it might be a rod bearing, although that noise gets worse with
revs, and my engine quieted down.  I have heard an engine with a definitely bad rod
bearing, and there is no doubt about it....it sounds like it wants to come apart, in
all directions, right now. 

I can't say I've ever heard a valve shim noise in a SHO engine.  The Lowrider had
one valve that was .002 looser than specified after 201k miles, and that one was
basically inaudible.....all its noises have been from noisy idler bearings and that
crank cancer.  I'd say that the sound should be fairly clicky, rather than hammery,
since the physical size of the parts we are talking about is very small, similar to
a valve tappet sound from an older V-8 with a collapsed lifter.

Let us know what it sounds like without the belts.

George