Engine Knock
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Joined: Aug 2004
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From: Lafargeville N.Y
Engine Knock
88' Coupe
Seems to have a low tone Knock at idle when at operating temp.If you bring it up off idle it goes away .It also "Knocks" when you first start it up when at operating temp for mabey 2 seconds.If i had a bad bearing,would'nt it knock when it was cold until it got oil pressure?I aquired the car when it had 85000 miles on it and was told it had a engine replacement at 50000 miles so the engine should'nt be that old to have a bad bearing should it?Could it be a bad oil pump? Great pressure cold but only 15 to 20 pounds hot.Sometimes 25 lbs
sorry for the somewhat long post,but i need help
Seems to have a low tone Knock at idle when at operating temp.If you bring it up off idle it goes away .It also "Knocks" when you first start it up when at operating temp for mabey 2 seconds.If i had a bad bearing,would'nt it knock when it was cold until it got oil pressure?I aquired the car when it had 85000 miles on it and was told it had a engine replacement at 50000 miles so the engine should'nt be that old to have a bad bearing should it?Could it be a bad oil pump? Great pressure cold but only 15 to 20 pounds hot.Sometimes 25 lbs
sorry for the somewhat long post,but i need help
Burning Brakes
Joined: Nov 2004
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A 'loose' piston or wrist pin will generally knock when the engine is cold, then quiet down as the heat expands the piston.
A 'bad' rod bearing will usually get worse (noisier) as the engine heats up, because the oil will thin out (and oil pressure drops off slightly) as it warms up. Depending on how bad, or loose, the rod bearing is, the noise may get softer as you rev the engine because you are running the oil pump faster, increasing oil pressure. Then, when you let off the throttle, your oil pressure goes back down and the noise returns. If you REALLY rev it HARD, for several seconds you may start to hear the knock get worse from the constant hammering of the high cylinder load/pressure, regardless of oil pressure.
Connecting rods, cranks, and bearings don't expand with heat as much as aluminum pistons will.
A 'bad' rod bearing will usually get worse (noisier) as the engine heats up, because the oil will thin out (and oil pressure drops off slightly) as it warms up. Depending on how bad, or loose, the rod bearing is, the noise may get softer as you rev the engine because you are running the oil pump faster, increasing oil pressure. Then, when you let off the throttle, your oil pressure goes back down and the noise returns. If you REALLY rev it HARD, for several seconds you may start to hear the knock get worse from the constant hammering of the high cylinder load/pressure, regardless of oil pressure.
Connecting rods, cranks, and bearings don't expand with heat as much as aluminum pistons will.
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Joined: Aug 2004
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From: Lafargeville N.Y
Would'nt a lifter have a "Tick" sound to it ?This sounds like a low toned Knock.I guess it would be good news if it was a lifter
I forgot to mention that i now have 90500 miles on it ,but with it being a new motor @ 50000 mi.It seems premature to have bearing problems.
What do i do to furthur diagnose it?
I forgot to mention that i now have 90500 miles on it ,but with it being a new motor @ 50000 mi.It seems premature to have bearing problems.
What do i do to furthur diagnose it?
Burning Brakes
Joined: Nov 2004
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Engine longevity will depend on how the 'replacement/new' engine was assembled, and what parts were used. There are some extremely cheap rebuild components for SBCs out there. It is hard to know exactly what you have for internal/rotating assembly parts without having the exact specs, build sheet, or receipt for the new engine.
Find a shop with a car hoist and stand underneath the car while it is running, revving it and shutting it off/starting it up. Get as many people to listen to it as you can, and get several opinions. Too many other noises will 'bounce' off the pavement when the car is on the ground, and make diagnosis more difficult.
Find a shop with a car hoist and stand underneath the car while it is running, revving it and shutting it off/starting it up. Get as many people to listen to it as you can, and get several opinions. Too many other noises will 'bounce' off the pavement when the car is on the ground, and make diagnosis more difficult.
