Mysterious Block Noise... - Team Camaro Tech
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post #1 of 8 (permalink) Old Mar 7th, 02, 07:11 PM Thread Starter
 
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Finally got back to California to work on my (nearly stock) '68 327 2bbl. This engine has less than 500 miles. There is a noise at above 2000 RPM only (measured with a tach). It sounds like a rapping, and I can't find its source. It sounds like it is coming from the center of the block. I was thinking that the vibration of the engine was causing something in the compartment to hit something else. The whole engine shakes in unison with this rapping, and at about 3,500 RPM or so the engine steadies, but the noise continues. So I doubt this is the case.
Fearing a spun rod bearing or bent wrist pin, I removed each spark plug wire one at a time, and still, no change. Removed the power steering pump, still no change. The only other accessory on the car is the alternator. Could I have piston slap? How can I tell? Could my crank be hitting the pan? How can I tell? Just because the noise didn't stop with the removal of the plugs, does that mean that the trouble isn't in the pistons? Could it be an exhaust leak? Could it be detonation? Any pointers, ideas, etc, would be most and much appriciated. Thanks!
Ryan
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post #2 of 8 (permalink) Old Mar 8th, 02, 12:38 AM
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Welcome to the club, I hope you enjoy your stay.

The noise ...from the center of the block, only at 2000 RPM and above, engine shakes w/ knock?

About the only thing I know would be weak valve springs, causing the lifter to float, thereby slapping against the cam lobe, and this is what you're hearing, or a bad set of lifters, can't stay pumped-up. This is providing the oil pump is working good, 35-40 lbs @ 2500 rpm.

Others here may have some good suggestions.

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post #3 of 8 (permalink) Old Mar 8th, 02, 10:53 AM Thread Starter
 
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Thanks for the advice, Everett.
Here is some more information. I think you may be right. It has to do with the valve train somewhere... My oil pressure is close to 60 at 2500 RPM. When I remove the valve cover to adjust the lifters, I notice a ton of oil squirting out of the #7 pushrods(the rearmost piston), but #1 was barely shooting any. The closer you get to the front of the engine, the less the squirting.
That was my first observation. My second observation is this:
I removed the pushrods on the entire driver's (1,3,5,7) side of the engine, and then started the car. With only four cyllinders running (2,4,6,8), the noise decreased signifficantly. Should I replace springs, rods, lifters, and pushrods? Wouldn't the machine shop that rebuilt the engine have given me new ones, or is this not a common practice? Thanks!
Ryan
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post #4 of 8 (permalink) Old Mar 8th, 02, 11:37 AM
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There should be the same amount of oil from each end.

See if there is a 1/8 in pipe plug at the front of the engine block between the intake manifold and water pump on the pass side. If there is, put a mech gauge to it. This goes directly to the oil galley, should read the same PSI, if not 10 psi less than, as the pick-off point underneath the distributor.

If oil pressure is more than 10 psi difference form the rear, then I'd say there is too much bearing clearance at crankshaft.

Each web of the block has an oil channel from the main oil galley to the cam bearings then too the crank main bearings then out to rod bearings. Too much clearance somewhere, no oil pressure.

Where the cam bearings replaced? They should have been replaced if block was hot-tanked. If orig cam was re-used, each orig lifter to orig lobe should have been re-installed to each other. Otherwise, if they were mixed up, then a new set of lifters should have been installed. Lifters/lobes make their own wear pattern to each other, they hate to be mixed.

I would say you should go over your receipts from the shop and see what replaced. Was there a teardown inspection done? Was there a list of mandatory replacement parts? Discuss this with the service manager and listen to what he has to say.

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post #5 of 8 (permalink) Old Mar 8th, 02, 12:03 PM
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I had a Crank pully loose (wobble) on me and it was causing the same problem...
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post #6 of 8 (permalink) Old Mar 8th, 02, 07:33 PM Thread Starter
 
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I think I may have found the source of the problem. Unfortunately, my receipts are in Illinois. I should call the machine shop, if my problem isn't solved. Anyhow, I pulled off the pan and I noticed that my oil pump rod (that goes to the distributor) was not connected properly. It didn't have that nylon ring. I must have forgotten it. Though I thought I did install it. So the rod, although it was spinning the pump, was probably clattering around in there. But the noise was a bit louder than just a clattering. It seemed like a rapping from the valve train! So I am not sure that replacing that ring will solve the problem. It's so hard to tell with engine noises! Anyhow, I'll let you all know on Monday (have to leave for a bit tomorrow to monday). I think the oil pressure is fine, but I'll try that tomorrow. Thanks, all!
Ryan
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post #7 of 8 (permalink) Old Mar 12th, 02, 10:47 AM Thread Starter
 
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Well, replacing the nylon ring did not solve the noise. I removed the intake manifold to check lifters and I think they may be bad. (See my other post, bad lifters?) The springs look brand new, I think the problem is in the lifters. The oil pressure is within 5 psi all around.
Thanks for all of your help.
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post #8 of 8 (permalink) Old Mar 13th, 02, 12:30 AM
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Sounds like you found the problem.

Good man!!

Now, when you change for new ones, be sure to break them in correctly, just as if you were doing a camshaft change, only for 10-15 minutes.

Be sure to adjust correctly before start-up. Turn crankshaft to intake starting to close, Turn exhaust push rod by hand, tighten adjusting nut till contact, then 1/4-1/2 half extra turn. Turn crankshaft to exhaust starts to open, adjust intake same way.

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