Over the past 6 months, I've had an engine tap that kept getting worse. I need help in deciding what it may be.

CAR:
90K miles on 1999 C5 FRC
65K miles on Vette Drs. Head/Cam/Headers package
35K miles on Cartek clutch
10K miles on new Oil pump

Ran well for a long time with the above configuration before the tapping began. At first, it was real quiet, now its almost louder than the engine itself.

SYMPTOMS:
Clutch makes a "metal on metal" noise when launching (maybe related or not)
Loud internal tapping that is directly related to RPMs
Tapping occurs in any gear and in neutral
Tapping occurs with clutch engaged or disengaged
Tapping SEEMS to be toward rear of block
Tapping SEEMS to be loadest underneath the car
Tapping SEEMS to come from passenger side
Basically, right where the starter is

REMEDIES
I have removed the heads. All valve train components seem to be OK.
No loose rocker arms or spacing between push rods and rockers.
Pushrods are straight as an arrow.
Lifters are in great shape. No obvious wear marks. None are "stuck".
Piston heads are not gouged. All valves are in good order.
Cylinders look ok. No obvious gouging from rings.
No piston or combustion chamber has any more carbon than any other.
Did not remove cam but did not see any obvious marks on lobes.

SYNOPSIS
I am not a trained mechanic so subtle things may escape my eye, however, it does not seem to be a valve train problem. I don't think its a piston slap problem since the cylinders look ok and the car was never noticbly burning oil. It is either a bottom end problem (bearings, a ring problem I do not see, etc.) OR something with the clutch / flywheel / starter.

Does anyone have any other ideas? Am I wasting my time thinking its the clutch/drivetrain? Obviously, having to pull the engine is the most expensive and since I don't have a lift it will be the hardest to do. I know its difficult to make a diagnosis without hearing anything but any suggestions will be greatly appreciated.

Thanks,
Tony


[Modified by Byter, 8:54 AM 2/23/2004]

 

It sounds like you already checked everything that I was thinking but if it were me, I'd check the clutch before pulling the motor.
Do you have any metal shavings in the oil, cut the filter open and look there also.
Goodluck :cheers:

 

Sounds like you have checked the usual suspects. On a wild hunch, check the exhaust, and especially the heat shields on the cats.

 

Something to consider might be the frequency of the noise. If It is say clutch,flywheel,rod or crankshaft making a noise every revolution, at 800 RPM you would hear it about 13 times a second. If it is a valvetrain noise it would most likly be about 3 times a second. If it is say a piston pin making a noise each time that cyl fires, it would also happen about 3 times a second.
It is another way to look for a noise.

 

Have you tried the stethoscope (vacuum hose in the ear) to locate the exact place the knock is happening?

:cheers:

 

runamuk - I will check the oil. It has been changed in the past, no outward signs of metal, but I wasn't really looking for it.

iflubyu - Yeah, thanks. I had that problem on other cars. It's the first thing I looked for.

flyin' brian - Much closer to the three (3) taps per second than the thirteen (13). Think a bad pin could be it (yuck)? It certainly would explain it getting louder as time passed. Is there a way to test this from the top end?

wwwashing - How about the 'ol screwdriver to the ear. Problem is that the noise is so loud now that you can hear it everywhere. Also, I now have the car torn apart so I can't recreate it until I put it back together. As mentioned before, this analysis sent me to a block location right above the starter.

Thanks guys!

 

Pull the plug wire on each cylinder one at a time and see if that makes it go away, or if the sound gets softer

 

Thanks Brian, but right now the heads are off the engine! It looks like I'm past the point of no return unless you can think of a way to test it with the heads off...