RPM dependant rapping - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

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post #1 of 5 (permalink) Old Mar 17th, 03, 05:41 AM Thread Starter
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Join Date: Mar 2003
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My '68 327 (nearly bone stock) has a hard rapping sound that seems to come in at about 2500 RPM and above. Below that it is fine. This is a freshly rebuilt engine, and the problem happenned after about 20? miles of driving.

I removed all spark plugs one at a time, trying to find the cylinder making the noise, but there was no change in the noise with any plug, so I doubt it is a bearing. Plus I took off the pan, and saw no signs of problems in the bottom end. I replaced the lifters, thinking they were broken, and the problem was not solved.

Anyone have any ideas as to what is wrong with my engine? I am going to do a compresion test and buy a stethoscope tonight. Thanks for your help.
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post #2 of 5 (permalink) Old Mar 17th, 03, 07:07 AM
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Location: Socorro, New Mexico, USA
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Possibly a broken flexplate/flywheel. Had one go on an old blazer I had -made a terrible racket!! Hope it is nothing too serious!!
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post #3 of 5 (permalink) Old Mar 20th, 03, 04:14 PM Thread Starter
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Here is an update to my problem.
I tested the engine's compression, and all cyllinders fell within about 20 PSI of one another from 125-145 or so. I don't think that there are any problems there. I checked the flex plate and it seemed fine, but I did not drop the transmission or anything. Could this be detonation? Plus, MGAUGHAN3 suggested the harmonic balancer. How do you tell if it is going bad? It sure doesn't feel loose on the crank, even though it is not new. Thanks again.
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post #4 of 5 (permalink) Old Mar 20th, 03, 06:35 PM
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Matt Jones
Join Date: Jan 2002
Location: Renton, WA USA
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Pulleys? Fan hitting shroud? Torque converter not engaged in pump? I'm just thinkin' out loud here...

Matt Jones
Lead Mechanical Engineer
Art Morrison Ent. Inc.
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post #5 of 5 (permalink) Old Mar 21st, 03, 04:15 AM
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Could be detonation, get a timing light with an advance, keep total timing less than 32^ as a start...


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