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Jay-231

Engine knocking

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87 Cutlass salon 307 went for drive ran fine parked it came back out later in the day started it and now it's knocking. The car has been well cared for oil changes on time wasn't even my every day driver any suggestions where to start problem shooting at? 

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If YOU are going to fix it, you need to drop the pan NOW.

See what is in the bottom with a magnet, and you know you are going to have to pull the rod and main caps and start looking for scored surfaces.

They will tell you where to go from there

 

Best of luck...........

 

Mike in Colorado

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My experience with the 307 ends with the 1968 model. ( disclaimer). I would start by pulling and replacing sparkplug  wires one by one while engine is running. If knock goes away on a particular cylinder when wire is pulled you know it’s probably a valve train, bearing, or piston problem on that cylinder.

If knock doesn’t go away while pulling wires, I would check torque converter bolts. Make sure they’re tight. Very rare instances of harmonic balancer causing unusual noises. 

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1 hour ago, Jubilee said:

My experience with the 307 ends with the 1968 model. ( disclaimer).

 

You are aware that the OP's 1987 307 is an Oldsmobile-sourced motor and is completely unrelated to the Chevy 307, right?

 

To the OP: obviously the knocking sound could be bearings, valvetrain, or something completely unrelated like a cracked flexplate or loose torque converter. Normally I would suggest checking for a loose outer ring on the harmonic balancer, but the Olds 307 doesn't use a rubber-mounted ring so this isn't a possible failure mode. Pulling the pan pretty much means pulling the engine. I would start by draining the oil and checking with a magnet as suggested above.

 

Frankly, if it IS a spun bearing, the motor already needs a rebuild, so you might as well unbolt the converter from the flexplate, remove all the accessory drive belts, and fire it up briefly to see if the noise is still there. If it is, try to determine if it's valvetrain or deeper down inside the motor.

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1 hour ago, Jubilee said:

I would start by pulling and replacing sparkplug  wires one by one while engine is running. If knock goes away on a particular cylinder when wire is pulled you know it’s probably a valve train, bearing, or piston problem on that cylinder.

 

That would be my first step. I've found you get more reliable results if you raise the RPM slightly above idle and then vary the RPM up and down just a little.

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Could be a chuck of carbon on the piston top.

I had it happen on a 500 Caddie Eldo.

Sprayed a misting of water down the carb...it went away.

Pull the plug wires first as mentioned.

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Does it knock at idle,?

more upon acceleration,?

more noticeable if you rev slightly and hear it as the revs come down? - this symptom cold be more a rod bearing than a main bearing.

 

But I agree that first start with removing one sparkplug wire at at time to listen for differing sound,

also have seen carbon cause similar symptoms-

 

Let us know what you find

Edited by Marty Roth (see edit history)

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