My 87 has roughly 92,000 miles on it. I'm hearing a random knocking that sounds like a bearing up front by where the accessories mount. Using a screwdriver as a stethescope, I hear the most noise by the A/C compressor idler bearing but the noise is still there when the A/C is running. Maybe the tensioner, PS Pump, or Alternator... Does anyone have experience with which one of these tends to fail the most. Everything I've mentioned is original equipment. The noise is not noticeable above, say, 1000 RPM and is louder after the car warms up slightly.
I'm not sure which goes out more than the others, but a few years ago I had a similiar knock that was coming from the front of the motor. It turned out to be the cam sensor, the bushings wore out and it would ride up the cam gear and smack the ring on the cap. I'd check that since your car is original. I had another knock noise coming from my alternator, but that just turned out to be when I was working with my coil and wires I accidentally got two wires switched, so I guess when the car was trying to fire a cylinder at the wrong time it wasn't working and causing a back flow of juice to the alternator, not sure what was going on but when I put the wires on the correct posts, the noise stopped. Try the screwdriver on all the accesories you can get to, including the cam sensor cap and try to narrow it down from there. I can say this, my a/c compressor was bad, but never knocked, it squealed, but who knows. Let us know if you figure it out. Also, you said it's not noticeable over 1000rpm, is that using your hand on the throttle or riding around? With riding around, engine and road noise can cover it up. Try to check it with the car sitting still, probe the screwdriver around on everything and vary the rpms, it might help locate the problem. But with it getting louder when the car warms up, would usually point to something that works with the oil, it heats up and the oil gets thinner, and with an increase in rpm, you also get more oil psi which if somethings tolerance was going or was off the more oil psi in there, the slack would be taken up, which again would point to something like a bearing, but I could be wrong, I don't want to scare you, just don't discount it, and I hope it's something much easier and cheaper to fix. Hope that helps,
Scott
Thanks, Scott, I'll check the cam sensor tonight but my screwdriver check didn't point to that piece. Lifting the cover off is real easy so no problem to check.
If I put the screwdriver on the A/C clutch hub (w/o the A/C on of course), I hear it pretty loud. I may remove the belt and run the engine for a very short time w/o the accesories and see if it is quiet then.
You're right, I sure do hope it is not the main bearings. Wouldn't the noise be more rythmic if it were a bearing? The noise does not sound internal but who knows at this point.
We just had a similar intermittent knock on our 87 T-Type Limited @ 94k.
It knocked sporadically at idle, but the knock disappeared at fast idle. Subjectively, it sounded like the knock eminated from the front of the engine. The knock became loud and persistant on a road trip.
The autopsy revealed metal powder and metal flakes in the oil and everywhere! Autopsy also revealed a spun REAR main, and a spun #5 rod bearing as well as a forward migration of the crank as if it had a trans brake or a standard transmission (neither was the case). Trashed a good turbo too.
We think it was related to insufficient oil pressure plus unknown driving and maintenance hx (was a recent purchase @ 92k miles).
Wish we had . . . . .
Thanks for the encouraging words...I just had everything apart to do a rear seal and chain... no metal flakes/debris anywhere. Needless to say I was very pleased. The noise was the same before I did all this work which is why I didn't bring it up before. I.e. the work I did didn't affect the noise one bit. I did not check the bearing clearances on the mains or rods when I had the pan down. Oil pressure at Idle, hot is 20 psi, at 40 mph it is about 40 psi, rather good, I'd say.
Still, this noise is more of a rattle rather than an engine knock.
I'll keep looking.
I do thank you for your help.
I think it is the tensioner. I checked the cam sensor for signs of rubbing, nothing noticeable. Then I started the engine and relieved tension on the belt and the noise went away. I think the noise is more noticeable at warm idle because it is a little rougher at the lower RPMs and the tensioner has to move more. Even when I move the tensioner w/o the engine running it squeaks so..
I'll post here after I've installed the new one.
I HAD THE SAME PROBLEM AT AROUND 190K IT WAS THE TIMING CHAIN AND TENSIONER
we are experiencing the same kind of noise and someone diagnosed it as a cam button gone bad, but since we are going that far we are changing everything out at once. I know that won't narrow it down, but we had a buick grand national guy tell us what was causing the issue. We will let you know on Monday how it went.
mine was the crank sensor ( same sounds)
Problem Solved:
It was the tensioner. Now, everything is quiet.
Thanks to everyone for their help