93 Deville main bearing thump
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HT4100 4.1, 4.5, 4.9 Discussion, 93 Deville main bearing thump in Cadillac Engine Technical Discussion; Hi everyone how are you doing I have a 93 cadillac deville 4.9 with the main bearing thump and im ...
  1. #1
    mike93 is offline Cadillac Owners Fanatic
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    93 Deville main bearing thump

    Hi everyone how are you doing I have a 93 cadillac deville 4.9 with the main bearing thump and im wondering if i should change the main bearings?

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    hcaddy95's Avatar
    hcaddy95 is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    I noticed my 95 does it to sometimes especially in hot weather. All the threads, I read every body said use 15w40 rotella T or delvac which i never did i use 10w40 valvoline sync power and never heard it again.

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    Ranger's Avatar
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    Re: 93 Deville main bearing thump

    Our old Guru always said it was annoying, but harmless. Use the 15W40 oil hcaddy suggested or live with it (if you can). GM does have a service bearing to replace it with if you want to go through the trouble.

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    Re: 93 Deville main bearing thump

    All you need to change is #1 bearing, as Ranger mentioned there are actually 2 undersize replacements. I did the job on an 88 I used to own years ago. It wasn't a real bad job. I ended up using the smaller undersize bearing that they had. Special order, I think they were $40 each from the dealer back then. I plastigaged the existing #1 bearing, I believe it was about .0022 clearance. Not bad as far as bearings go, but I remember the guru stated that anything over .002 would give the thump. I had to loosen all the main bearing caps to let the crank hang, to swap the bearing out. I ended up with .0016 or so with the second undersize and it was quiet.

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    I think im gonna change the bearing because im using the rotella 15w40 and the knocking is very loud still with the rotella at idle and when accelerating u hear it but not at wide open throttle

  7. #6
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    Re: 93 Deville main bearing thump

    How are you certain that what you hear is a main bearing?

  8. #7
    mike93 is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    it's gotta be that idk what else it could be the egr is brand new throttle body is clean egr tubes are clean and everyone says when it don't do it at wide open throttle thats the main bearing thump

  9. #8
    hcaddy95's Avatar
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    Re: 93 Deville main bearing thump

    You could take your belt off and start the engine and see if you hear it. you will be able to pin point the sound if it is your main bearing thumping

  10. #9
    drewsdeville is offline Cadillac Owners Master
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    Re: 93 Deville main bearing thump

    I'd like to add that though the #1 is the one that makes the noise, there are service replacements for TWO positions. #1 and #5. The theory that I've been taught by the local dealer and by a specialty place called "The Caddy Shop", the aluminum block distorts over years of heat/cooling cycles. It creates a scenario where, with the added clearance after distortion, the crank "teeter-totters" and makes noise.

    I've also found an unlikely theory on the internet that the serpentine belt tension can cause this bearing wear...but I just don't buy that.

    I've posted the part numbers before. If you are interested, do a search.

    If you want to be certain before spending the money, I'd take some plastigauge to the mains first. I'm pretty sure dropping the pan on your deville should be really easy, as it was still when they used a crossover for the exhaust.

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    ok i will try that first because i gotta take offthe pan anyway because the oil pan gasket is leaking and i like to try to fix my car because im in school for auto mechanic so i can practice on the car a lil

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    Re: 93 Deville main bearing thump

    I remember the guru saying that the trhe serpentine belt tension is what contributed to the problem, as it kept trying to lift the crankshaft and when number one cylinder fired, it pushed back down, rocking the crank a bit. I do not remember him saying anything about number 5 bearing. All I did when I diagnosed mine was to take some tension off the belt while it was idling in gear, and the noise went away.......I also remember the guru saying they changed the block on the 4.9's to eliminate the problem. On my 95 I used to own, it was doing it with 160k miles on it. But my 88 did it with half of those miles on it.

  13. #12
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    Re: 93 Deville main bearing thump


  14. #13
    mike93 is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    should i change the block it only has 102,000 miles on it

  15. #14
    Ranger's Avatar
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    Re: 93 Deville main bearing thump

    Hell no!
    morgue.delivery likes this.

  16. #15
    drewsdeville is offline Cadillac Owners Master
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    Re: 93 Deville main bearing thump

    Quote Originally Posted by bigtone View Post
    I remember the guru saying that the trhe serpentine belt tension is what contributed to the problem, as it kept trying to lift the crankshaft and when number one cylinder fired, it pushed back down, rocking the crank a bit. I do not remember him saying anything about number 5 bearing. All I did when I diagnosed mine was to take some tension off the belt while it was idling in gear, and the noise went away.......I also remember the guru saying they changed the block on the 4.9's to eliminate the problem. On my 95 I used to own, it was doing it with 160k miles on it. But my 88 did it with half of those miles on it.
    What? Every accesory system on any engine pulls up on teh crank... If it didn't there wouldn't be any tension on the belt. IF it's the belt that causes it, why doesn't the northstar exhibit the same problem? How about a Toyota 4 cylinder? That doesn't explain why only this particular engine knocks. No offense to this "guru", but that sounds absurd. A belt causing main bearing wear?

    It doesn't make sense when you consider that on any engine, the crank never actually touches the bearings. It always rides on a film of oil. THe only way to create clearance is to either run it out of oil, eliminating the film, or create main bearing clearance through dirty oil wear or distortion.

    I'm not trying to be offensive, just trying to understand. Anyone remember the explaination he gave for this?

    Either way, I can confirm the service bearings in both postions...I installed them in my '95 two years ago. THe number 5 is a green bearing, and the number one is blue or purple, I can't remember which.

    edit: I found the part numbers I had posted two years ago:
    Here are the current part numbers for the bearings if anyone is interested...

    (#1 position, service: 3545719)blue
    #2 AND #4 positions: 12489577
    #3 position: 3545721
    #5 position: 3545722
    (#5 position, service: 3545723)green

    All installed, engine still purrs to this day. Just as quiet as a new lexus V8

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