rgshafto Posted August 20, 2008 Share Posted August 20, 2008 I've got about 2,000 miles on a rebuilt 1936 Pontiac 6 flathead motor. From the beginning, it has made an odd noise when revved in a certain rpm range. It is coming from the front of the engine, sounds like a knock. I know it isn't:• a generator bearing;• the water pump or fan;• engine bearings, pistons or valves;• the inner oil splash pan;• anything loose on the car that might vibrate (gas line, etc.)• the distributor.I'm wondering if it might be either the harmonic balancer or the timing chain/gears. The balancer is original and worked fine before the rebuild. The new timing chain was new, but the timing gears are original (impossible to find NOS gears). I've never had a problem with either of these, so I don't know what they sound like when they are not functioning properly. Or maybe its the engine mounts? Any suggestions/advice most welcome. Thanks. Link to comment Share on other sites More sharing options...
Ron of Chicago Posted August 21, 2008 Share Posted August 21, 2008 Can you get it to make the noise when the car is sitting still?Removal of the belt will eliminate the generator and water pump. Link to comment Share on other sites More sharing options...
rgshafto Posted August 21, 2008 Author Share Posted August 21, 2008 Yes, the car doesn't need to be in motion. Already removed the fan belt and it made no difference. Link to comment Share on other sites More sharing options...
Ron of Chicago Posted September 10, 2008 Share Posted September 10, 2008 Have you thought about taking the car to the guy that did the rebuild? Maybe he could listen to it and figure it out. Link to comment Share on other sites More sharing options...
Guest Pete Woodruff Posted September 11, 2008 Share Posted September 11, 2008 Bob, is the knock a deep, solid sound similar to a rod knock? Typically chain driven camshafts don't knock like gear driven cams do because chains don't impart thrust; but it is possible the cam is "walking" in and out due to varying loads from the oil pump. Can you tell if the sound is loudest at the timing cover, or the engine block just above the cover? The most common engine to be plaqued with loud camshaft knocking was the 4 cylinder "Iron Duke" engines used in the '80s and early '90s in GM X & N body front wheel drive cars. They had gear driven cams and if the cam gear had excessive clearance the knocking could be heard 100 feet away! Link to comment Share on other sites More sharing options...
rgshafto Posted September 15, 2008 Author Share Posted September 15, 2008 It's more of a "hollow knock" Pete, so the current theory is that I may have a bad piston. Compression check comes next, so we'll see. The rebuilder is some distance away, so haven't had it back to him. Thanks for weighing in everyone. Link to comment Share on other sites More sharing options...
Guest docmiller13 Posted March 8, 2011 Share Posted March 8, 2011 hmm..I have the same issue with my 27 pontiac...its like a slapping sound coming from the upper half of the motor.....the engine sat for 20 years...got her running last week...not sure if I should let her run and the sound is normal or be worried..... Link to comment Share on other sites More sharing options...
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