Engine Noise Diagnosis
 

Just reinstalled my rebuilt 3.6 in my 993. Engine starts and runs fine. Great oil pressure. Just needs to be broken in. Sounded great. Took it for a short drive and on returning to my garage, I became aware of a "new" noise. Sounds like a loose bracket in the area of the bell housing. I can make the noise disappear by depressing the clutch. Other than the noise, the car seems to operate perfectly.

I recall having a similar noise before tearing down the motor, and since I did not find anything loose in the clutch assembly, I came to the conclusion that the source may have been the light weight flywheel fitted to the car to replace the dual mass flywheel.

Assuming the noise is related to the flywheel.....what am I actually hearing? And, why does depressing the clutch pedal make the noise disappear?

At first I was surprised by the noise, which was not there on initial startup nor during the initial 30 minute run-in on the motor to lap in the rockers and cams. The run in was done in my garage by holding engine speed to about 2500 rpm for 30 minutes. The noise only appeared after a short drive.

Lastly, I did fit the powertrain with a replacement transmission. Its a Motorsports G-50/34 and its fitted with a Porsche LSD. No experience with this transmission yet. The box is used but had been reconditioned by a reputable rebuilder.

Since the engine and transmission appear to be operating normally, I am inclined to just drive the car and monitor the noise. If the noise is unchanged when I've completed the engine break-in, I'll assume that it is OK.

The engine rebuild was a stock rebuild except for the addition of Web Cam RS hydraulic cams and RS 52mm inlet valves. Also had the ECU reprogrammed to take advantage of the cam and valving changes.

Break-in oil is Brad Penn 30wt Break-In oil which I plan on dumping at 1000 miles. I did change out the oil once after the 30 minute run-in.

Any comments/advice would be appreciated.