Searching for a knock...
Thread Starter
Racer
Joined: Nov 2008
Posts: 293
Likes: 1
From: Eaton Ohio
Searching for a knock...
I've been working on this car for a little while...here is the past thread if you wanna read... http://forums.corvetteforum.com/c3-t...ans-no-go.html
So..I have a knock..
I pulled both valve covers and all rockers move just fine
I pulled each plug one at a time to see if the noise went away..and it did not...
It is a hard metal knock sound...possible a lifter I thought...maybe a cam isssue...or main bearing?? I'm trying anything I can do with out pulling the engine, but I think my options are out on that one unless you have any more recommendations?
I'm moving from Hawaii to Ohio in January..I'll pull it then..
I just want it in safe running condition if I can so that I can ship it as a "running car" so it is cheaper...other wise they charge tow it all around their parking lots and what not...
So..I have a knock..
I pulled both valve covers and all rockers move just fine
I pulled each plug one at a time to see if the noise went away..and it did not...
It is a hard metal knock sound...possible a lifter I thought...maybe a cam isssue...or main bearing?? I'm trying anything I can do with out pulling the engine, but I think my options are out on that one unless you have any more recommendations?
I'm moving from Hawaii to Ohio in January..I'll pull it then..
I just want it in safe running condition if I can so that I can ship it as a "running car" so it is cheaper...other wise they charge tow it all around their parking lots and what not...
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
Have you used a long dowel or rubber hose to 'listen' to various accessories or parts of the engine?
The fuel pump has been known to fool people into thinking there was a rod knock, same for some exhaust leaks and probably water pumps as well. I would take a listen to these parts and see if the knock is louder at one than the other.
Also try that trick on the oil pan. Get the car up on jack stands so it's safe, start it, and slide under it making sure to stay away from the hot exhaust and fan. Listen to the pan. If the knock is louder at the pan then you probably have a spun rod bearing. They can still knock even with a plug removed.
The fuel pump has been known to fool people into thinking there was a rod knock, same for some exhaust leaks and probably water pumps as well. I would take a listen to these parts and see if the knock is louder at one than the other.
Also try that trick on the oil pan. Get the car up on jack stands so it's safe, start it, and slide under it making sure to stay away from the hot exhaust and fan. Listen to the pan. If the knock is louder at the pan then you probably have a spun rod bearing. They can still knock even with a plug removed.
Drifting
Joined: Aug 2008
Posts: 1,381
Likes: 11
With the engine idling, either short the plug wire to each cylinder or remove it , one at a time, just like you said you did. The RPM should decrease an equal amount for each cylinder and the noise should change or go away when you hit the right one. If the noise never changes and the RPM drops equally for all cylinders move onto step 2. Drain the oil into a clean container. Strain it if you have something to strain it with (paint strainers work good). Go in through the drain hole with a small magnet and fish around. At the very worst you'll have to use your fingers in the oil and look for shiny particles or chunks. Magnetic particles usually mean cam or lifters. non-magnetic particles will mean bearing material. Obviously you want none of the above. If you find no metal, run the engine with the belts off. If you still have the knock and the car has an auto trans look hard at the flex plate. A cracked or broken one will sound just like a rod knock and many people have sold cars for cheap because they thought the engine was bad when all they had was broken flywheel. Good luck.
Melting Slicks
Joined: Mar 2006
Posts: 2,465
Likes: 0
From: Orange Park Fl
God bless, Sensei
Team Owner
Joined: Aug 2006
Posts: 24,125
Likes: 15
From: Columbia Missouri
A hose is good for vacuum leaks but I don't know about knocks. A dowel can be dangerous stuck in your ear as you move around a running engine. Go to the auto parts store and buy a mechanic's stethoscope (about $15). As the engine runs, move the probe around to different places. You should be able to find the source.
God bless, Sensei
God bless, Sensei
Actually a small length of plain heater hose works great for this purpose.
Melting Slicks
Joined: Dec 2000
Posts: 3,363
Likes: 303
From: Lansdale 19446 PA
2024 C3 of the Year Finalist- Unmodified
St. Jude Donor '10-'11, '15, '19
If it is a main bearing - the knock would have gone away when the plug wire was pulled. Don't ask me how I know this
