New main bearings

[skyman]

After driving my 91 Eldo around with that #1 main bearing thumb, I'm finally getting around to fixing it. I remember Allen Cline told me that it was only necessary to replace the #1 bearing to get rid of the knock. But I'm thinking that since I've been driving it around for a while that maybe I should replace all 5.

Now, I can get a complete set for $75 at Carquest Auto Parts or I can get them from the dealer for around $74 a piece. Are the bearings from the Caddy dealer really better or am I paying an inflated price for OEM parts?

[BodybyFisher]

If I were you, I would get the bearings from Cadillac. They have a service bearing (purple?) that has the proper clearances to make up for the bearing knock... With aftermarket, its anyone's guess. I was considering doing this job on my 91. I also had discussed this with Mr. Cline a long time ago and he was saying that all that really needed replacing was the #1 bearing. Obviously you can replace them all, I just don't know if they can be done without pulling the engine and weather the top bearing can be rolled out. I would look into that.

Try www.gmotors.com I use them all the time, Mike

[skyman]

If I were you, I would get the bearings from Cadillac. They have a service bearing (purple?) that has the proper clearances to make up for the bearing knock... With aftermarket, its anyone's guess. I was considering doing this job on my 91. I also had discussed this with Mr. Cline a long time ago and he was saying that all that really needed replacing was the #1 bearing. Obviously you can replace them all, I just don't know if they can be done without pulling the engine and weather the top bearing can be rolled out. I would look into that.

Try www.gmotors.com I use them all the time, Mike

Thanks Mike. I was under the impression from my previous chats with Al Cline that it could be done with the engine in the car by just dropping the pan. In fact I think I remember someone on this board doing bearing replacment on their car from underneath.

[BodybyFisher]

Yes, I agree that the #1 can be done with the engine in the car, the question in my mind is can ALL the bearings be done with the engine in the car. I would confirm that before I purchased all the bearings. I was only interested in getting rid of the #1 bearing knock, so I was only doing #1.. Good Luck and definately post your experience and progress.. Mike

By the way, before I bought my car, they replaced the pan gasket with the engine in the car, the pan comes down. You will also find that MATT dropped his pan with the engine in the car as it was leaking on the engine I got for him...for some reason

[adallak]

Yes, you can replace #1 with engine in the car. Removing the pan is tricky but possible. I'll try to post bbob's comments on the issue and related repair procedurs later troday. Mike is correct, GM replacement bearing is known as "purple".

Here is something from Mr. Cline:

"In general, you are all describing the main bearing thump that is not too uncommon on the 4.9... It is the crank moving up and down in the front main bearing due to just a .0001 too much clearance....LOL. The basic reason the engine is sensitive to front main clearance is that the serpentine belt pulls the crank up and the combustion loads push it down....thump...thump...thump.... Completely harmless but annoying.

You can confirm that this is the problem by loosening/removing the serpentine belt so that there is no side load on the crank pulley and run the engine. If the noise disappears then that is the problem. Often you can easily duplicate the noise by getting the engine good and hot and have a helper LIGHTLY power brake the engine against the torque converter while holding the brakes. Once you can duplicate the noise then just use a breaker bar in the square drive lug on the belt tensioner to loosen the belt so that it slips. The noise will suddenly go away with the relaxed belt tension if that is your problem.

An easy possible solution is to switch to a slightly heavier oil such as the 15W40 Delo/Delvac/Rotella brands of heavy duty diesel oil available in gallon jugs at discount stores most everywhere. That is a preferable oil for the 4.9 anyway since that engine still has a distributor gear on the cam that appreciates the extra antiwear package in the HD oils. The extra viscosity will help the main bearing thump.

There are service front main bearings specifically released for the service of units with this issue and they are available at any Cadillac Dealer. It requires dropping the pan and replacing the front main bearing. It can be done with the engine in the car and is not too difficult but a bit time consuming.

Try the oil first and if that quiets it down then forget about it. In any case, it will not hurt the engine in the least (the main bearing thump) but it is annoying in some cases.

When the engine is hot hold the brakes, put it in drive and lightly load the engine against the trans (power brake it) to see if you can duplicate the noise in the driveway. If so, then loosen the accessory belt to see if the noise goes away. If the noise dissappears when the accessory belt is loosened then it is the front main bearing thump as described. This is a simple and easy check to see if that is the problem.

Yes, there is a service main bearing for the car. Only the one main bearing is replaced....just the front one....with the special bearing. The bearing can be replaced with the engine in the car as the oil pan can be removed with the engine in the car and the front main replaced. I have no idea how much is costs to have done..... Only the Cadillac service parts has the special service front main for the main bearing thump. Aftermarket bearings will not have the special clearance and special shape required for the main bearing thump fix.

The main shell will rotate out with the crank in place. Take the front main cap off and use a small screwdriver and mallet to tap on the edge of the upper main shell that is on the opposite from the locating tang. It will loosen and rotate around the crank. Slide/rotate it on the crank main 180 degrees and it is in your hand. Rotate the new, service bearing into place the same way. It really isn't tough to do at all. Pulling the pan is the hard part. To remove the pan in the car you have to rotate the crank so that the counterweights will clear so there is some trial and error involved but it is not that difficult.

[BodybyFisher]

Thanks Adallak that was great info, Mike

As we see, only the #1 is critcal for the knock.. I assume that it can be done with all the bearings however if someone cared to do that..

[bschelle]

Thanks Adallak that was great info, Mike

As we see, only the #1 is critcal for the knock.. I assume that it can be done with all the bearings however if someone cared to do that..

I have 118,000 on my 91 Eldo. I switched to the Rotella oil and the thump has gone away. Just my 2 cents worth!

[KHE]

Thanks Adallak that was great info, Mike

As we see, only the #1 is critcal for the knock.. I assume that it can be done with all the bearings however if someone cared to do that..

The purple service bearing is only for the #1 main bearing on a thumping 4.9. It is not to be used in any of the other positions as it may bind the crankshaft.

[skyman]

Yes, you can replace #1 with engine in the car. Removing the pan is tricky but possible. I'll try to post bbob's comments on the issue and related repair procedurs later troday. Mike is correct, GM replacement bearing is known as "purple".

Here is something from Mr. Cline:

"In general, you are all describing the main bearing thump that is not too uncommon on the 4.9... It is the crank moving up and down in the front main bearing due to just a .0001 too much clearance....LOL. The basic reason the engine is sensitive to front main clearance is that the serpentine belt pulls the crank up and the combustion loads push it down....thump...thump...thump.... Completely harmless but annoying.

You can confirm that this is the problem by loosening/removing the serpentine belt so that there is no side load on the crank pulley and run the engine. If the noise disappears then that is the problem. Often you can easily duplicate the noise by getting the engine good and hot and have a helper LIGHTLY power brake the engine against the torque converter while holding the brakes. Once you can duplicate the noise then just use a breaker bar in the square drive lug on the belt tensioner to loosen the belt so that it slips. The noise will suddenly go away with the relaxed belt tension if that is your problem.

An easy possible solution is to switch to a slightly heavier oil such as the 15W40 Delo/Delvac/Rotella brands of heavy duty diesel oil available in gallon jugs at discount stores most everywhere. That is a preferable oil for the 4.9 anyway since that engine still has a distributor gear on the cam that appreciates the extra antiwear package in the HD oils. The extra viscosity will help the main bearing thump.

There are service front main bearings specifically released for the service of units with this issue and they are available at any Cadillac Dealer. It requires dropping the pan and replacing the front main bearing. It can be done with the engine in the car and is not too difficult but a bit time consuming.

Try the oil first and if that quiets it down then forget about it. In any case, it will not hurt the engine in the least (the main bearing thump) but it is annoying in some cases.

When the engine is hot hold the brakes, put it in drive and lightly load the engine against the trans (power brake it) to see if you can duplicate the noise in the driveway. If so, then loosen the accessory belt to see if the noise goes away. If the noise dissappears when the accessory belt is loosened then it is the front main bearing thump as described. This is a simple and easy check to see if that is the problem.

Yes, there is a service main bearing for the car. Only the one main bearing is replaced....just the front one....with the special bearing. The bearing can be replaced with the engine in the car as the oil pan can be removed with the engine in the car and the front main replaced. I have no idea how much is costs to have done..... Only the Cadillac service parts has the special service front main for the main bearing thump. Aftermarket bearings will not have the special clearance and special shape required for the main bearing thump fix.

The main shell will rotate out with the crank in place. Take the front main cap off and use a small screwdriver and mallet to tap on the edge of the upper main shell that is on the opposite from the locating tang. It will loosen and rotate around the crank. Slide/rotate it on the crank main 180 degrees and it is in your hand. Rotate the new, service bearing into place the same way. It really isn't tough to do at all. Pulling the pan is the hard part. To remove the pan in the car you have to rotate the crank so that the counterweights will clear so there is some trial and error involved but it is not that difficult.

Thanks...that's a great help.