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Re:Try to isolate the noise to the top or... (archive)
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Posted by Randy on November 21, 2001 at 19:27:02:

In Reply to: Re:Try to isolate the noise to the top or... posted by Richard '83 533i Houston on November 21, 2001 at 07:46:07:


bottom end of the engine. Old trick from my gearhead hotrodding days. With the engine at idle, take a long shafted screwdriver, put the end of the blade firmly against the engine block as low as you can easily get it on the suspect cylinder. Now put your ear against the handle end of the screwdriver and listen to the sound. Do the same for say the numer 6 cylinder and see if it sounds different.

My WAG, is that you may have a conrod bearing that is excessively worn and it's causing the ticking/knocking sound. At high RPM yo may have had the piston actually impact the plug electrode.

My $.02

Rich

Hello! This is a follow up question answered by Ian. My M5 has 230,000+ miles on it. It consumes only 1/2 quart of oil every 2,500 miles. I've thought of rebuilding or at least a valve job, but mechanics say "if it isn't broken...don't fix it!" Through the years (I've owned car since new) I have been noticing a light metallic tapping that is in sych with engine speed at any temp. At first I though it was a maladjusted valve. I have also been told that it is a normal noise fuel injectors make. A week ago my #3 sprark plug broke while accelerating at 6,000 rpms. It caused the car to misfire and replacing the plug seemed to solve the problem. The ceramic surrround was chipped and the electrode bent to a "no gap" configuration. Now, I swear the tapping noise is MUCH louder! I'm afriad something horrible has happend and the M5 is ready to die?! The car seems to be running fine although I haven't applied full throttle yet. Ian sugested getting a compression check done. I will also do a visual inspection of the valve train. Any ideas what my be wrong with my baby?



Ran your diagnosis by a mechanic friend and he said that if it was a conbearing, the knocking would only be present under engine load. my noise is constant regardless of engine speed or load. I will just have to take the cover off next month when I have time to do more investigating. thanks for your input

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