4.9 main mearing thump getting worse?
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HT4100 4.1, 4.5, 4.9 Discussion, 4.9 main mearing thump getting worse? in Cadillac Engine Technical Discussion; Hi everyone how are you? This morning when I started my car to go out it was knocking loud for ...
  1. #1
    mike93 is offline Cadillac Owners Fanatic
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    4.9 main mearing thump getting worse?

    Hi everyone how are you? This morning when I started my car to go out it was knocking loud for like a minute or two then stopped and did the same thing just before just a minute or two car never did it this bad Ive been using 15w40 rotella in it egr tubes clean everything new just started yesterday I always have a knock at low speeds and not at wot just wondering is my main bearings getting worst or what cars running great just the knock no codes either thanks for the input

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    drewsdeville's Avatar
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    Re: 4.9 main mearing thump getting worse?

    Get that 15W-40 out of there. Don't buy into that rumor. The car was spec'd for 10W-30, use nothing else.

    I got the same cold start knocking when I tried the 15W-40, which I regret and am embarrassed that I fell for this myth. As soon as I drained it and added the correct weight, knocking disappeared. You can't solve the main bearing thump with oil. If you want the knock to go away, replace the main bearings.

    This is assuming that you've narrowed the knock to the main bearing thump and have eliminated all other possibilities.

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 4.9 main mearing thump getting worse?

    Ok i was gonna take that out and put 10w30 in there should I use High mileage and yes i narrowed it down to the main bearings how hard of a job to replace the bearing and which bearings do you need to replace?

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    Re: 4.9 main mearing thump getting worse?

    Quote Originally Posted by mike93 View Post
    Ok i was gonna take that out and put 10w30 in there should I use High mileage and yes i narrowed it down to the main bearings how hard of a job to replace the bearing and which bearings do you need to replace?
    Not bad at all if you don't have a crossunder pipe to worry about. I'm pretty sure on the '91-'93 a crossOVER pipe was used, running over the top of the trans. Therefore, the oil pan should be wide open for you to remove. Just drop the pan and you have access to all of the main bearings.

    The clearance develops in the #1 and #5 positions, but I'd recommend you replacing all 5 if you are going through the work of replacing any. Do it once and do it right.

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 4.9 main mearing thump getting worse?

    Yeah your right you do them on your car? should I use high mileage 10w30

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    Re: 4.9 main mearing thump getting worse?

    Yes, I did them on my '95 4.9. I had a crossunder pipe, so removing the exhaust was the hardest part. After that it was a breeze.

    Any 10W-30 will work fine.

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 4.9 main mearing thump getting worse?

    ok sorry to be a pain how long did it take you to do them all say if i don't have the crossunder pipe?

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    Re: 4.9 main mearing thump getting worse?

    I don't know, 2 hours, with being careful? Just remove the pan, loosen bearing caps, R&R each bearing one by one applying a liberal amount of assembly lube, apply RTV in the grooves on the #5 cap. Torque them all down, install oil pan and gasket. Done!

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 4.9 main mearing thump getting worse?

    Wow pretty fast how much were the bearings? I bet that car is quiet as shit now

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    Re: 4.9 main mearing thump getting worse?

    I actually can't remember at all how much it was. The "service" bearings for #1 and #5 were slightly more expensive from what I remember, but I don't know how much.

    Yes, if shit is quiet, my car is quiet as shit now.

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 4.9 main mearing thump getting worse?

    Ok last question sorry can I get them online parts place or only go to dealer?

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    creeker is offline Cadillac Owners Connoisseur
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    Re: 4.9 main mearing thump getting worse?

    Quote Originally Posted by mike93 View Post
    Ok last question sorry can I get them online parts place or only go to dealer?
    Dont know, try rockauto.com

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    mike93 is offline Cadillac Owners Fanatic
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    Re: 4.9 main mearing thump getting worse?

    ok i always use rock auto great prices thanks

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    steelybill is offline Cadillac Owners Enthusiast
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    Re: 4.9 main mearing thump getting worse?

    If it's the original engine, the bearings will be standard, likely. If it's a replacement/rebuilt engine, they may be under size. Maybe Rock Auto guys will know about the bearings if it's original. Ask questions.

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    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 4.9 main mearing thump getting worse?

    drewsdeville, did those bearings slip into place easily with the crank still in the engine? It seems like it would be a tight fit to me. I ran 15-40 in my Deville for 3 years in below 0 weather with no knocking. It did turn over slow in the cold weather though so now it has 5-40. I can't kill this engine, I want to retire the car but it runs too nice and shifts sooo smooth with 194k on the clock. I'd sell the engine if somebody wanted it bad enough, if not I'll just drive it another year.

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