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HT4100 4.1, 4.5, 4.9 Discussion, 93 Deville main bearing thump in Cadillac Engine Technical Discussion; I didnt say that the tensioner created wear at the bearings. ...First off, not all tensioners create lift on the ...
  1. #16
    bigtone's Avatar
    bigtone is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    I didnt say that the tensioner created wear at the bearings. ...First off, not all tensioners create lift on the crankshaft. 4.1,4.5, and 4.9's, due to the pulley routing, apply their tension straight up. Northstars, for example tend to apply the tension at about a 90 degree an angle, toward the front of the car, not straight up because of the way the belt routes around. Most other engines are like this also. What the Guru said was even with a normal bearing clearance at number 1 bearing, the lifing of the crank by the belt along with the downward force from the cylinder firing creates the main bearing noise. As I stated, mine was at .0022 clearance, which is still pretty good for an engine with 80k miles, but it was enough to allow the crank to move enough to create the noise. I never knew about the #5 bearing replacement, he only talked about #1. In fact, I remember him saying that the other bearings had to be on the looser side in order to run a tighter than normal bearing on #1. When I did mine which was around 2002 or so, GM offered 2 undersized bearings for number 1, I had to use the smallest to end up with .0016 clearance.
    If the tensioner was not a contributor of the problem, why would releasing the tension make it stop? The Guru, after all, had a hand in designing these engines.

  2. #17
    drewsdeville is offline Cadillac Owners Master
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    Re: 93 Deville main bearing thump

    I wondered about the belt tension thing until I tried the test that supposedly confirms it.Releasing the belt never quited my knock, yet the bearings were indeed the problem...

    And there are PLENTY of engines where the accessory drive pull straight up on the crank. One familiar one (for me) that comes to mind is the Ford 4.6 and 5.4, which are known for their tight and strong bottom ends...

    How about for a jeep v6?



    Almost doesn't get any more straight up than that. Even the 4.X isn't as nice and vertical as that.

    The belt pulling straight was was very common up until recently when accessory packaging became more complicated with front wheel drive and downsizing.

    If the belt pulling up and the cylinders firing are causing the wear, then why doesn't the bottom bearing shell wear on every other engine (that does NOT have the belt pulling up) from the constant pounding from the cylinders firing.

    In the end, to each man his own. I'd more likely trust a dealer and specialty shop that I've spoken to face to face than a mysterious "guru" behind the keyboard.

    I guess we'll never understand the phenomenon without someone actually disassembling and analyzing an affected engine, which, to my understanding, no one has done.

  3. #18
    mike93 is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    one day someone will understand when i find out what the problem is because like i said im going to school for mechanics so when the car has between 200,000 - 250,000 miles im gonna take the motor apart and rebuild the motor

  4. #19
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    Re: 93 Deville main bearing thump

    Not sure about the accuracy of your drawings, but 7-25 shows the tension lifting the crankshaft not straight up, but the vector is actually at about 330 degrees or so. I'm sure the angle is not straight up (000) by design. Also the other drawing shows the angle at about 15 degrees. If you dont understand this, look in a mechanical reference or talk to a Mechanical Engineer. Did you measure the clearance with your original bearings? Maybe they were excessively worn and what you were hearing was not main bearing thump, but regular old bearing knock.

    Again, I never said this causes bearing wear, it is a combination of uplift and cylinder firing causing opposite motion in the same plane, and the normal running clearance of the bearing that causes the noise.

    As far as disassembling and analyzing engines with this condition, Cadillac did many because they replaced a ton of these engines under warranty because of the knocking.

    Read this.....http://www.caddyinfo.com/howto4pt9bearingthump.htm

  5. #20
    mike93 is offline Cadillac Owners Fanatic
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    Re: 93 Deville main bearing thump

    ok well no matter what later on im gonna rebuild the motor no matter what

  6. #21
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    Re: 93 Deville main bearing thump

    I'm not trying to be offensive, just trying to understand. Anyone remember the explaination he gave for this?
    I think he said (as mentioned) it was because the tension is pulling straight up.

  7. #22
    drewsdeville is offline Cadillac Owners Master
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    Re: 93 Deville main bearing thump

    Quote Originally Posted by bigtone View Post
    Not sure about the accuracy of your drawings, but 7-25 shows the tension lifting the crankshaft not straight up, but the vector is actually at about 330 degrees or so. I'm sure the angle is not straight up (000) by design. Also the other drawing shows the angle at about 15 degrees. If you dont understand this, look in a mechanical reference or talk to a Mechanical Engineer. Did you measure the clearance with your original bearings? Maybe they were excessively worn and what you were hearing was not main bearing thump, but regular old bearing knock.

    Again, I never said this causes bearing wear, it is a combination of uplift and cylinder firing causing opposite motion in the same plane, and the normal running clearance of the bearing that causes the noise.

    As far as disassembling and analyzing engines with this condition, Cadillac did many because they replaced a ton of these engines under warranty because of the knocking.

    Read this.....http://www.caddyinfo.com/howto4pt9bearingthump.htm
    Here's the belt routing for a 4.9 . It, to, is not even close to perfectly pulling up at 0 or 360 degrees either...



    Bearing thump = bearing knock. Noise from excessive main bearing clearance is the same, regardless of if you want to call it a knock or thump. I think 4.x owners just gave the noise a "thump" name because it doesn't seem to affect longevity. "knock" is more of a harsh word, usually goes along with terminal failure.


    This is taken from the link you posted:

    "One item to remember is that the main bearing clearances take into account any main bearing bore misalignment, any crank straightness or runout tolerances and any thermal distortion of the block or main bearing bores. One would not want to put the tighter clearance service bearing in all of the main bearing locations as there would be insufficient clearance to allow the crank to rotate freely and there would be a high likelyhood of a main bearing "pinching" on the crank and "spinning" said bearing. Not good. The service (tighter fit) purple bearing shell should only be used on the front main and in no other location nor in any other location in conjunction with the front main bearing location. "

    However, just like this supposed guru behind the keyboard, there's no credibility in either of these statements. Random posts such that website aren't very credible sources...

    Again, to each man his own.

    Cadillac replacing engines under warranty is an economic decision by cadillac, not an explanation of the problem.

    Furthermore, if the knock was caused by the accessory drive design, why would they bother replacing the engine with another that has the same "faulty" accessory drive?? Wouldn't solve the problem...

  8. #23
    steelybill is offline Cadillac Owners Enthusiast
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    Talking Re: 93 Deville main bearing thump

    The "teeter-totter" explanation is a good one!! The factory calls it "crankshaft whip"

  9. #24
    sweetgn is offline Cadillac Owners Member
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    Re: 93 Deville main bearing thump

    Hello,

    I have the issue with what I figure it a bearing knock when the engine is first started when cold. It lasts for about 3-4 minutes then goes away. I have inquired at the GM dealer for these bearings especially the service bearings and they tell me they are discontinued. Does anyone know if any aftermarket manufacturers are including the service bearing sizes in the normal standard size replacement kits?

    Thanks,

  10. #25
    drewsdeville is offline Cadillac Owners Master
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    Re: 93 Deville main bearing thump

    A 3-4 min "knock" most likely isn't bearings. Periods of 3-4 minutes of bearing knock would destroy an engine quickly. Also, a bearing knock wouldn't disappear after the warm-up period.

    In 1990, the 4.X's recieved a new style piston and cylinder liners (The '90 4.5 got most of the 4.9L updates, including 4.9 heads, intake manifold, pistons and liners). These engines were prone to piston slap - the piston rocking in it's bore. When the pistons expand as they warm, the extra tolerance goes away and the knock disappears.

    This was remedied shortly after with a piston update, but I'm not quite sure exactly when it happened. My '95 4.9 never made any noise whatsoever. However, in the winter months, my '90 "knocks" for a few minutes on a morning cold start, subsiding in about 2 minutes. It has done this for years, since I purchased it.

    That said, there's not much harm in this. As long as the knock disappears when the engine is warm, don't worry about it. It's a little annoying, but nothing that should be a cause for concern.

  11. #26
    the recluse is offline Cadillac Owners Connoisseur
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    Re: 93 Deville main bearing thump

    Is it a knock or a rattle. The idler or tensioner pulley(s) can leave the same sound under the hood. Disconnect the belt and run to see if the sound goes away. If it doesn't it may be a valve train rattle, in which case I would change the oil and filter; a good place to start for that problem.

    Keep us posted...

  12. #27
    sweetgn is offline Cadillac Owners Member
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    Re: 93 Deville main bearing thump

    Thanks for the replies so far. This is on a '91 Deville 4.9. I did not notice this problem near as much as when the temperatures were in the 70's or above this summer. Now that it is colder, on a cold start it knocks near the bottom of the front of the engine(I had the front wheel and sound insulators removed so I could see the belt and crank pulley. It might only last about 2 minutes. It is very noticeable, but it does completely stop after a few minutes of running. I have tried the trick of loosening the idler pulley to reduce tension on the crank pulley while running. This did not help the problem. I did not take the belt completely off, however I have just changed to the 15w40 and Lucas Oil Treatment and that did not make the sound go away or get any better. Thanks for the advice on the pistons. It saved me some money on the bearings.

  13. #28
    the recluse is offline Cadillac Owners Connoisseur
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    Re: 93 Deville main bearing thump

    Quote Originally Posted by sweetgn View Post
    I have just changed to the 15w40 and Lucas Oil Treatment and that did not make the sound go away...
    God, no wonder ....I don't know where you're at, but anything north of Atlanta right now your oil's got to have the consistency of mud at any temp around 40 deg. or less. It can't circulate through the block and all your doing is destroying the bearings AND the valve train. Get that out of there and go to 5w30 for the winter

  14. #29
    rayjuswa is offline Cadillac Owners Member
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    Re: 93 Deville main bearing thump

    Drew
    I need bearings to fix my 1995 Deville 4.9 engine bearing thump and can't find them anywhere My deville is excellent otherwise with only 60,000 miles
    Can you help me!
    Rayjuswa@aol.com

  15. #30
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    Re: 93 Deville main bearing thump

    Talk to Chris (Rippy) over there >>>>>>>>>>>>>>

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