1979 big block knocking sound
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1979 big block knocking sound
ok so recently there's this knocking sound that started coming from the engine of the corvette and at first it start very very quite but in the matter of 30 min it became super loud and hard to where it seemed like I'd blow the engine so I got it towed home. I talked to someone that knew about older car engines and he said that a rod bearing might of blew or something and he said I'd be able to see the problem from the oil pan but after taking it off I can't seem to find anything wrong nothing cracked or disconnected (I'm 19 and have no mechanical experience) I'm a diy kind of guy and wanted to see if I could find the problem myself so this is my last resort before I take it to a shop lol
Safety Car
Joined: Apr 2006
Posts: 4,057
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From: BC
That does sound like a rod knock. Does the knock quiet down under acceleration then get very noisy when you let off the gas? You will not be able to see anything wrong until you take the connecting rod caps off and check the bearings. The bad one will be easy to spot as it sounds like it has already pounded itself to death.
Thread Starter
Intermediate
Joined: May 2016
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That does sound like a rod knock. Does the knock quiet down under acceleration then get very noisy when you let off the gas? You will not be able to see anything wrong until you take the connecting rod caps off and check the bearings. The bad one will be easy to spot as it sounds like it has already pounded itself to death.
Racer
Joined: Sep 2011
Posts: 414
Likes: 55
From: Humboldt county Ca
Did you find any metal in the pan? Lots of things can cause a knock. Wrist pins, slapping pistons, rod bearings, main bearings, etc.
If you have little mechanical experience, major engine work is not the place to start unless you have the tools, a hoist and a place to work. If it is a big end bearing gone bad the crank is most likely galled and will have to come out for reconditioning or replacement. If you have someone with the tools and experience to help you, by all means try it. Otherwise, this is a job for a shop.
Good luck!
If you have little mechanical experience, major engine work is not the place to start unless you have the tools, a hoist and a place to work. If it is a big end bearing gone bad the crank is most likely galled and will have to come out for reconditioning or replacement. If you have someone with the tools and experience to help you, by all means try it. Otherwise, this is a job for a shop.
Good luck!
Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
If this is a rod or main bearing knock you can't just replace the bearing. The crankshaft will also be damaged so you are looking at a rebuild. You can confirm it by checking the bearings but my opinion is it's time to pull the engine.
Thread Starter
Intermediate
Joined: May 2016
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Did you find any metal in the pan? Lots of things can cause a knock. Wrist pins, slapping pistons, rod bearings, main bearings, etc.
If you have little mechanical experience, major engine work is not the place to start unless you have the tools, a hoist and a place to work. If it is a big end bearing gone bad the crank is most likely galled and will have to come out for reconditioning or replacement. If you have someone with the tools and experience to help you, by all means try it. Otherwise, this is a job for a shop.
Good luck!
If you have little mechanical experience, major engine work is not the place to start unless you have the tools, a hoist and a place to work. If it is a big end bearing gone bad the crank is most likely galled and will have to come out for reconditioning or replacement. If you have someone with the tools and experience to help you, by all means try it. Otherwise, this is a job for a shop.
Good luck!
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Thread Starter
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Racer
Joined: Sep 2011
Posts: 414
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From: Humboldt county Ca
I'll try to help you a little. Pull all the plugs and get a torque wrench before you start pulling the rod bearings. Put a socket on the crank pully bolt and turn the crank till a crank journal is pointed down. Pull that rod cap and inspect it and the crank joirnal for burning, scratching, etc. Put the cap back on the same way it came off. Don't turn it around. Torque the rod bolts and then move to the next connecting rod. When you have finished that, check back and we will go from there.
Thread Starter
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I'll try to help you a little. Pull all the plugs and get a torque wrench before you start pulling the rod bearings. Put a socket on the crank pully bolt and turn the crank till a crank journal is pointed down. Pull that rod cap and inspect it and the crank joirnal for burning, scratching, etc. Put the cap back on the same way it came off. Don't turn it around. Torque the rod bolts and then move to the next connecting rod. When you have finished that, check back and we will go from there.
Racer
Joined: Sep 2011
Posts: 414
Likes: 55
From: Humboldt county Ca
First, Wait until you pull the rod caps and inspect the bearings. If nothing is wrong, you don't need new bearings. If something is wrong, the engine comes out. Common practice is to mill the crankshaft journals down on a rebuild and install oversize rod bearings. Just pulling out old bearings and putting in new ones generally helps nothing.
Yes, I mean the spark plugs. Makes the engine much easier to turn over by hand but you can do it without pulling the plugs.
I'll look up the torques but I need to know what year and which engine you have (427, 454). 79's didn't come with big blocks as far as I know.
Yes, I mean the spark plugs. Makes the engine much easier to turn over by hand but you can do it without pulling the plugs.
I'll look up the torques but I need to know what year and which engine you have (427, 454). 79's didn't come with big blocks as far as I know.
Thread Starter
Intermediate
Joined: May 2016
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First, Wait until you pull the rod caps and inspect the bearings. If nothing is wrong, you don't need new bearings. If something is wrong, the engine comes out. Common practice is to mill the crankshaft journals down on a rebuild and install oversize rod bearings. Just pulling out old bearings and putting in new ones generally helps nothing.
Yes, I mean the spark plugs. Makes the engine much easier to turn over by hand but you can do it without pulling the plugs.
I'll look up the torques but I need to know what year and which engine you have (427, 454). 79's didn't come with big blocks as far as I know.
Yes, I mean the spark plugs. Makes the engine much easier to turn over by hand but you can do it without pulling the plugs.
I'll look up the torques but I need to know what year and which engine you have (427, 454). 79's didn't come with big blocks as far as I know.
Burning Brakes
Joined: Apr 2008
Posts: 1,222
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From: shelbyville West Michigan
if it's a 350, it's not a big block.
I would have let someone experienced listen to it before tearing into it, especially with no experience on engine internals. rod knocks vs. main bearing knock is different. lifters/cam/valves sound different. cracked flex plate sounds different, there are a number of things it could be without jumping to ripping the engine apart, but you are already there.
you can inspect the bearings as noted above, but do you know what you are looking for? if not, post pics of each bearing and crank area as you remove them. guys on here will help.
even a picture of the oil/inside of oil pan will help some.
I would have let someone experienced listen to it before tearing into it, especially with no experience on engine internals. rod knocks vs. main bearing knock is different. lifters/cam/valves sound different. cracked flex plate sounds different, there are a number of things it could be without jumping to ripping the engine apart, but you are already there.
you can inspect the bearings as noted above, but do you know what you are looking for? if not, post pics of each bearing and crank area as you remove them. guys on here will help.
even a picture of the oil/inside of oil pan will help some.
Thread Starter
Intermediate
Joined: May 2016
Posts: 32
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if it's a 350, it's not a big block.
I would have let someone experienced listen to it before tearing into it, especially with no experience on engine internals. rod knocks vs. main bearing knock is different. lifters/cam/valves sound different. cracked flex plate sounds different, there are a number of things it could be without jumping to ripping the engine apart, but you are already there.
you can inspect the bearings as noted above, but do you know what you are looking for? if not, post pics of each bearing and crank area as you remove them. guys on here will help.
even a picture of the oil/inside of oil pan will help some.
I would have let someone experienced listen to it before tearing into it, especially with no experience on engine internals. rod knocks vs. main bearing knock is different. lifters/cam/valves sound different. cracked flex plate sounds different, there are a number of things it could be without jumping to ripping the engine apart, but you are already there.
you can inspect the bearings as noted above, but do you know what you are looking for? if not, post pics of each bearing and crank area as you remove them. guys on here will help.
even a picture of the oil/inside of oil pan will help some.
Thread Starter
Intermediate
Joined: May 2016
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Ok so it's been a while since I've touched the car (life kinda got in the way) but today I put it all back together and put some new oil to figure out which cylinder was making the noise pulling the plugs and turning on the car( I figured out on my own that pull the plugs while the car is on shocks the **** out of u so now I know lol) and found out it's the driver side 2nd from the front is making the knocking noise so next weekend when I hav time I'll drain the oil again and take a look at that piston
Racer
Joined: Sep 2011
Posts: 414
Likes: 55
From: Humboldt county Ca
Sounds like you have a wrist pin going south. Getting that piston out will require either dropping the crank or pulling the drivers side head. The pan will have to come off either way. Since you have it running again can you find someone to help you with it that knows something about it or take it to a shop? If a wrist pin has come loose and slid out enough to score the cylinder bore the engine will need a rebuild. Others may have a better handle on what's happening then me but taking the spark off a cylinder and having it quiet down is the usual symptom of a wrist pin.
Thread Starter
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Ok so I just got out from under the corvette and I took the oil pan off to look at that piston that I pull the spark plug from and it stopped making noise so I'm try to pull the rod caps off and it just does not wanna come off so I start tapping all the other rod and there was on the I could completely shake with my hand and it wasn't that one that I pulled the spark plug from. I got a video https://youtu.be/b0kDU0Y7fKQ now all the other ones I couldn't shake but this one could it be this rod causing the noise?