Jay-231 0 Posted September 3 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? Share this post Link to post Share on other sites
FLYER15015 423 Posted September 3 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 Share this post Link to post Share on other sites
Jubilee 11 Posted September 3 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. Share this post Link to post Share on other sites
joe_padavano 1,116 Posted September 3 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. Share this post Link to post Share on other sites
Ronnie 1,296 Posted September 4 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. Share this post Link to post Share on other sites
c49er 238 Posted September 4 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. Share this post Link to post Share on other sites
Mikefit 91 Posted September 4 C49 Has the correct answer put him at the front of the class. Share this post Link to post Share on other sites
avgwarhawk 3,096 Posted September 5 What kind of knock? Octane or lower end mechanical knock? Share this post Link to post Share on other sites
Marty Roth 1,317 Posted September 8 (edited) 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 September 8 by Marty Roth (see edit history) Share this post Link to post Share on other sites
