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Old 10-27-2008, 05:25 PM
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Need rod bearing help ASAP! PLZ

First off I m not an Engine Man, but I understand how most of it works.
I have developed the suspected "rod knock" in a 1962 GM 283 that I was told was gone thru, was now 60 over, and had about 5K miles on the rebuild. The guy I got the motor from is a Buddy so I tend to think it's close to the truth.
I have read a ton of stuff about all the things that can be mistaken for a "rod knock".
The knock sounds deep toned, changes with engine speed, BUT it goes away sometimes, or at least gets a little better.
I drained the oil.....it looked Ok did not see any evidence of metal in the oil, dropped the pan, not metal there either.
I tried to shake each rod. I get a little side to side movement, but can't get any sense of being loose like a bearing was really worn out.
2 of the rods are a different color though. At first I thought it was rust but it seems to be colored that way. The rod cap, and the rod are brown up to where the actual skinny part of the rod begins. I thought at first it was discoloration from heat but after looking closer it looks like they are just that way for some reason. The 2 rods that are differnt colored are NOT on the same journal.
I have not split open the filter yet, but I will. I did not see any evidence of metal there so far though.
If the bearing was bad, would I be able to tell by just trying to shake it?
The plugs are still in.
The oil pressure has been 50 at start up. 40 when warmed up and driving, and drops off to 20 at a 600 rpm idle.
The filter was a GM filter....I think it was pretty old.
It has been changed over from the canister filter to a spin on.
If this sounds OK, I guess it's time to pull the covers and look at the valve train.
I did put my hand on the fuel pump, and did not feel anything like a knock.
Sorry this is so long, just trying to answer the questions that might be asked.
Thanks for the great website!!!!!!!!

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Old 10-27-2008, 06:01 PM
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Usually, the items associated with the term "Rod Knock" are;

Rod Journal.....The rod bearing is the normal suspect, but it may also be a "Egg" shaped rod end, which can be easily diagnosed by measuring the rod journal end with the rod cap bolted down and torqued to spec, you will need to measure across the journal and then 90� to it, the measurement should be the same, though it is not unusual to see them egged out 0.010 to 0.020".

Piston Slap.....This is a condition that sounds very much like a Rod Bearing going out. It's caused by the piston being able to rock in the bore, and every time the direction changes, from up to down, the piston rocks over and slaps the cylinder wall, creating a loud slapping noise. Usually this is caused by the piston having abnormal wear, the cyclinder having abnormal wear or sometimes it might be caused by some one putting the wrong size piston back in at time of rebuild. Say the engine was bored oversize by 0.060" and the guy rebuilding the engine accidentally put back in a piston of stock or even 0.020" or 0.030" oversize.
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Old 10-27-2008, 06:19 PM
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Next time try pulling off one spark plug wire at a time and goosing the engine. If it is a bad rod or rod bearing the noise will usually completely disappear if there is no combustion in the cylinder. Unless the rod or rod bearing is completely worn out. In any case, since the oil pan is off why not pull the rod caps off one at a time and look at the bearings. It's very easy to spot a bad bearing when looking at them. I'd start with the discolored rods.
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Old 10-27-2008, 06:25 PM
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Btw, usually a rod knock is loudest immediately after the decel point when you rev the engine.
Usually a piston slap will decrease considerably or disappear completely as the engine warms up, unless the piston is very, very bad.
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Old 10-27-2008, 06:31 PM
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Quote:
Originally Posted by CustomConspiracy
First off I m not an Engine Man, but I understand how most of it works.
I have developed the suspected "rod knock" in a 1962 GM 283 that I was told was gone thru, was now 60 over, and had about 5K miles on the rebuild. The guy I got the motor from is a Buddy so I tend to think it's close to the truth.
I have read a ton of stuff about all the things that can be mistaken for a "rod knock".
The knock sounds deep toned, changes with engine speed, BUT it goes away sometimes, or at least gets a little better.
I drained the oil.....it looked Ok did not see any evidence of metal in the oil, dropped the pan, not metal there either.
I tried to shake each rod. I get a little side to side movement, but can't get any sense of being loose like a bearing was really worn out.
2 of the rods are a different color though. At first I thought it was rust but it seems to be colored that way. The rod cap, and the rod are brown up to where the actual skinny part of the rod begins. I thought at first it was discoloration from heat but after looking closer it looks like they are just that way for some reason. The 2 rods that are differnt colored are NOT on the same journal.
I have not split open the filter yet, but I will. I did not see any evidence of metal there so far though.
If the bearing was bad, would I be able to tell by just trying to shake it?
The plugs are still in.
The oil pressure has been 50 at start up. 40 when warmed up and driving, and drops off to 20 at a 600 rpm idle.
The filter was a GM filter....I think it was pretty old.
It has been changed over from the canister filter to a spin on.
If this sounds OK, I guess it's time to pull the covers and look at the valve train.
I did put my hand on the fuel pump, and did not feel anything like a knock.
Sorry this is so long, just trying to answer the questions that might be asked.
Thanks for the great website!!!!!!!!
YKnot got most of it. I'll add that rods, piston skirts, and pins develop a double knock. For each revolution you get a knock at the top and bottom of the stroke for the rod or the pin. You get the same double knock from the piston skirt as it passes thru the loading from the thrust side to the non-thrust side and back again.

The difference between them is the heaviness of the tone and this is something that's hard to put into words. I guess I'd say the rod is more of a solid knock where pin and piston skirt are a higher tone but not quite a click.

The fact the engine holds good oil pressure would push me away from thinking this to be a rod. The pressure loss across a bad rod or main is easy to see in oil pressure and your's is right on spec for a small block.

That said, if this is the typical double knock, that would aim me at a cracked piston skirt, an incorrectly sized piston, or a pin gone bad. Don't laugh about the incorrect size piston, I've seen more than one engine bored to an oversize with less than that oversize pistons put in it.

If it's a single knock, especially at half engine speed that would aim you at the cam and valve train. A heavy single knock would be associated with mains, but again the engine's holding good pressure, especially at idle, an indicator the problem lies elsewhere, but as these things go not a guarantee just a good probability.

Get yourself a stethoscope and probe around, you may get a better idea of where and what the sound is.

Bogie
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Old 10-27-2008, 06:50 PM
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Since you have the oil pan off, just start at the front and work to the rear pulling each rod cap off and looking at the bearing. When putting the cap back on just make sure the little tang that fits tight in the little grove have to match up. If you have a spum bearing, you will see where the bearing has spun in the cap, and the rod I.D. machined surface will be all ground up. If it is a bad bearing, you need to pull the motor, break it apart, send the crank off to be reground, and have the rods reconditioned, or find another motor. By cutting the filter apart, spread out the wafer paper of the filter and look for the presence of metal, copper is the underlayer of the top layer of bearing, and it's the only place in the engine you will find copper. Don't forget to check all the rods and retorque them after the inspection.
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Old 10-27-2008, 08:39 PM
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Thanks Soooo much

Thanks for all the good stuff. I'll get a stethoscope tomorrow, and also pull off the valve covers and have a look.
This is my daily driver and shop truck (65 c10) and I really want to avoid pulling the engine if I can.
Thanks again for all the good stuff that happens on this site!
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Old 10-27-2008, 09:12 PM
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Before you dig too deep into this so called rod knock, take a close look at the timing cover. Check for any new raised areas on the depression sides of the cover for a loose bolt on the timing cam sprocket that is hitting the inside of the cover. I had this occur back in the 60s on a sbc327 in my Nomad. It drove me crazy when I pulled all the caps in the rods and couldn't find a thing wrong. Put in all new bearings and STILL had a noise that sounded just like a rod bearing. One bolt had come loose and was hitting on the depressed areas of the timing cover and sounded JUST like a rod knock. As I pulled off the water pump I could see a distinct circle where the cam sprocket bolt had been hitting the inside of the cover at the low dimpled areas. If knew that could happen, I would have looked closer and found it before I spent many many hours tearing the motor apart.
Just a thought!
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Old 10-29-2008, 06:12 AM
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Chasing the knock

So I put the pan back on, and rigged a strethoscope. With the help of my Son, we followed the knock BACK to somewhere around the flexplate.
I have a 89? 700R4 bolted up to this 62 283.
While I was checking around the timing cover, I stripped one of the pully bolts out, and noticed (I had been trying to ignore it) the harmonic balancer was trashed.....bad wobble.
I read up on Harmonic balancers, and didn't realize how important they are.
Now I gotta switch that out....there goes another hundred dollar bill...LOL
I dread pulling this trans back out, but I guess it gotta be done.
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Old 10-29-2008, 09:39 AM
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Make sure your torque converter bolts & flexplate bolts are tight. This can create the sound your talking about if they're loose. A cracked or broken flexplate can cause this sound also.
Harmonic Balancer Info>>
http://www.chevytech.com/2c44o6.html

http://www.chevytech.com/2c44.html
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Old 10-29-2008, 02:27 PM
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SSedan64.

Do you have a link to that web sites home page you can share ?





R
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Old 10-29-2008, 02:54 PM
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Quote:
Originally Posted by Rob Keller
SSedan64.

Do you have a link to that web sites home page you can share ?





R
Sure Rob, Just leave off the part past the /forward slash>>
http://www.chevytech.com/
You can click on individual parts in the Short Block & Head Sections also for Info. This is one of the easiest sites to navigate I've found.
Block Index
http://www.chevytech.com/2c000.html
Head Index
http://www.chevytech.com/3c000.html
Specifications
http://www.chevytech.com/1c1.html

Last edited by SSedan64; 10-29-2008 at 02:56 PM. Reason: More Info
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Old 11-29-2008, 05:20 PM
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About the knock????

After having to drive around listening to this thing, and being scared I was doing some terrible damage....It's my shop truck and driver so I kinda had to drive it till I could get it back on stands so I could get under it.
ANYHOW......I got the stethoscope and poked around.
The sound (knock) seems to be coming from a spot around the oil pan.
If you were looking at the pan from the side, the sound is centered about 3 inches from the rear about dead center on the side of the pan where the deepest part is.
If I probe the BOTTOM of the pan it's fine....but the side in the middle I can hear the noise.
When I had the pan off I found no metal and saw no evidence of anything rubbing or hitting, and I cleaned the whole inside of the pan. The oil pump screen looked clear.
I probed the bell housing, and around the flex plate and not much ....just the side of the pan.
Very strange.
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Old 12-01-2008, 02:46 AM
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I see that you mentioned two of the rod caps were discolored. These would be suspect, metal discoloration on rod or main caps is usually caused by heat, meaning possibly oil starvation, or severe wear causing the bearing to spin in the the rod. Usually ends with severe crank journal damage, however all 283's had forged cranks, which can take a little more abuse and still be reground. I would also check for small black pieces, they look like small grains or small rocks. They are actually hardened valve seals that have broken apart and found a way via the oil return passages through the motor and into the oil pan. This is quite common in high mileage older SBC's.
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