Need Help to Diagnose Rattle!

[SHO Mojo]

Gurus,

My 1989 (131K mi.) has developed a strange rattle/knock/growl. Note that engine power appears to be unaffected.

I used a stethescope to try and nail down the location, here is what I heared: It is definitely loudest on the pulley side of the rear cylinder bank and I believe it is louder on the exhaust cam side of that bank.

What I DIDN'T hear: I listened under the motor, and it does not make any noise down there, so I believe I can rule out rod bearings. I also was careful to listen to the cam chain end of the valve covers...no slapping or bad sounds at all from that end.

So, what do you think I'm looking at? Could it possibly be a loose timing belt? Or, am I looking at some very excessive valve clearance on one cylinder? Or, perhaps I'm hearing piston slap or a loose fitting wrist pin?

Any help is GREATLY appreciated! Thanks,

 

[SHO SPD]

Try putting the stethiscope on the valve cover itself, if ts louder there I would believe its something with the valves. on the head itsef, I'm not too sure.

 

[SHO Mojo]

SHOSPD...Thanks for the reply...I did indeed listen at the valve covers, intake and exhaust cams (at both pully and tranny ends of the motor). The exhaust cam area on the rear cylinder bank, nearest the pulley-end of the motor is noticeably louder than anywhere else.

While I might be led to guess a missing valve shim, it's just hard to believe I can have such a serious problem and not notice a driveabiliy issue. Could simple "open" clearance on a valve lash cause such a noise?

shrug

 

[SHO Mojo]

OK, some more info...

After driving home, with the car good and warm (my commute is only 11 miles, but lots of traffic backup allowed the engine to get fully warmed up), I again pulled out the stethescope and listened across both valve covers, both intake and exhaust cams.

Fully warm, the rear exhaust cam is still noisy, but it is lessened and the "rattle" at 1500rpm is noticeably reduced. So, I think my hypothesis is now excessive exhaust cam valve lash, especially on the rear cylinder bank. Open enough to cause extra noise when cold, but quiet substantially once "fully" warm. Make sense to anyone else?

 

[SHO SPD]

man, I say pull that valve cover off and take a peak, before anything gets damaged!