Engine Knock
Thread Starter
Racer
Joined: Aug 2008
Posts: 326
Likes: 5
From: central Florida Florida
Engine Knock
I bought this 1985 Vette 5 years ago. It seemed to drive and shift great before I started to do a mild restoration on it. Now that the car is finished..... paint, interior, Greenwood ground effects.... etc. etc. The car has a noticeable knock to it when warmed up. The oil pressure starts out at 40 psi then drops when warmed up. Took it out for a test drive and it seemed to lose power on the short drive home.
At this point I have put so much into it that I am thinking of dropping a $1500 crate motor into it, but before I do this, can it be something simple or are these the signs showing of a junk motor? Oh , also the balancer was spun and had to be replaced.
I checked the exhaust bolts, timing, tune up, fuel pump replaced. The car was in rough shape when bought 5 years ago and the mileage is unknown.
Thanks
At this point I have put so much into it that I am thinking of dropping a $1500 crate motor into it, but before I do this, can it be something simple or are these the signs showing of a junk motor? Oh , also the balancer was spun and had to be replaced.
I checked the exhaust bolts, timing, tune up, fuel pump replaced. The car was in rough shape when bought 5 years ago and the mileage is unknown.
Thanks
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,214
From: Park City Utah
What does the oil pressure drop TO?
Have you dropped the oil and looked at it?
Have you used a stethoscope or solid rod to narrow down where the noise is coming from?
Kill once cylinder at a time when it's making the noise. If the noise stops or changes significantly on one of the killed cylinders, that is your problem cylinder/bearing.
It could be a cracked or loose flex plate too.
Have you dropped the oil and looked at it?
Have you used a stethoscope or solid rod to narrow down where the noise is coming from?
Kill once cylinder at a time when it's making the noise. If the noise stops or changes significantly on one of the killed cylinders, that is your problem cylinder/bearing.
It could be a cracked or loose flex plate too.
Instructor
Joined: Feb 2014
Posts: 139
Likes: 0
From: Lakeland FL
Catalytic converter coming apart?
Jack it up and beat on the converter with a rubber hammer. If you can hear something rattling around in it, it's coming apart.
When they come apart, a lot of times that broken piece inside will rattle around and sound like a bottom end engine knock. Just not as consistent. Also it will restrict the exhuast (or plug it up) giving the loss of power symptom you have.
Just one more thing to check. Good luck
Jack it up and beat on the converter with a rubber hammer. If you can hear something rattling around in it, it's coming apart.
When they come apart, a lot of times that broken piece inside will rattle around and sound like a bottom end engine knock. Just not as consistent. Also it will restrict the exhuast (or plug it up) giving the loss of power symptom you have.
Just one more thing to check. Good luck
Thread Starter
Racer
Joined: Aug 2008
Posts: 326
Likes: 5
From: central Florida Florida
No converters on the car. Exhaust was replaced with new straight pipe. No codes either. Used stethoscope, but cant pinpoint dull knock. The balancer was bad also.... it scratched up the timing cover slightly. I will check pressure today, but I am thinking at one point it was like 5 at idle then goes back up to 20 when RPM increase. This is when motor is warmed up. Pressure starts out at 40 when cold. Oil is very clean. I will do some more checking today with some of the suggestions.
Thanks
Thanks
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Advanced
Joined: Jan 2014
Posts: 62
Likes: 0
From: Mt. Airy Md
No converters on the car. Exhaust was replaced with new straight pipe. No codes either. Used stethoscope, but cant pinpoint dull knock. The balancer was bad also.... it scratched up the timing cover slightly. I will check pressure today, but I am thinking at one point it was like 5 at idle then goes back up to 20 when RPM increase. This is when motor is warmed up. Pressure starts out at 40 when cold. Oil is very clean. I will do some more checking today with some of the suggestions.
Thanks
Thanks
Good luck Joe
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,214
From: Park City Utah
Le Mans Master
Joined: May 2006
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From: indy indiana
Thread Starter
Racer
Joined: Aug 2008
Posts: 326
Likes: 5
From: central Florida Florida
Ok, so I just removed trans inspection cover and all looks good. With a pry bar I noticed crank was able to move very little.... not sure what the tolerance is. I drained the oil and noticed it to be extremely thin. Replacing oil and filter just for fun to see if this changes anything. Also removed the plugs wires with no changes to sound. With the car in the air and running the noise does seem to be coming from the bottom or front of engine. Thanks for the replies.... could be the obvious, but willing to try a few things before biting the bullet.
Team Owner
Joined: Aug 2004
Posts: 21,543
Likes: 3,214
From: Park City Utah
Advanced
Joined: Jan 2014
Posts: 62
Likes: 0
From: Mt. Airy Md
Ok, so I just removed trans inspection cover and all looks good. With a pry bar I noticed crank was able to move very little.... not sure what the tolerance is. I drained the oil and noticed it to be extremely thin. Replacing oil and filter just for fun to see if this changes anything. Also removed the plugs wires with no changes to sound. With the car in the air and running the noise does seem to be coming from the bottom or front of engine. Thanks for the replies.... could be the obvious, but willing to try a few things before biting the bullet.
Good luck Joe
Last edited by just joe 2; Feb 23, 2014 at 04:32 PM. Reason: Add
Thread Starter
Racer
Joined: Aug 2008
Posts: 326
Likes: 5
From: central Florida Florida
Well I started tearing the motor apart, decided to just pull it. Interesting thing though, lower power steering pump bolt was loose. Made me think for a second... could this be making a bumping noise? Oh well too late motor should be out tomorrow.... sick of messing with it.
Advanced
Joined: Jan 2014
Posts: 62
Likes: 0
From: Mt. Airy Md
Well I started tearing the motor apart, decided to just pull it. Interesting thing though, lower power steering pump bolt was loose. Made me think for a second... could this be making a bumping noise? Oh well too late motor should be out tomorrow.... sick of messing with it.
Thread Starter
Racer
Joined: Aug 2008
Posts: 326
Likes: 5
From: central Florida Florida
Wow! So I jerked the motor out last week.... no problem. Got the new crate motor and dressed it up with the stuff that the motor came out with. Going back in,,,, not so easy. I am one that does a lot by myself, but man am I having a hell of a time getting these mounts to line up. spent about 2 hours with motor up and down and even took off the crank pulley for more clearance. Any suggestions would be well appreciated. I even changed chain position from front to back to side to side. I will tackle it again Wednesday night. Right now I just need to walk away from it for a day.
Melting Slicks
Joined: Jan 2014
Posts: 2,176
Likes: 378
From: Lunenburg MA
I just put mine back in on Sunday. Like all SBCs, I find the easiest way is to get one side lined up with a bolt through it (loosely) with the back of the motor supported about even to where it should be. Then if the other side is being a pain, I set the hoist up to just lift that side up a few inches and then release it as fast as I can (drop it effectively). After a few tries it usually lines right up.
Thread Starter
Racer
Joined: Aug 2008
Posts: 326
Likes: 5
From: central Florida Florida
I just put mine back in on Sunday. Like all SBCs, I find the easiest way is to get one side lined up with a bolt through it (loosely) with the back of the motor supported about even to where it should be. Then if the other side is being a pain, I set the hoist up to just lift that side up a few inches and then release it as fast as I can (drop it effectively). After a few tries it usually lines right up.