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HT4100 4.1, 4.5, 4.9 Discussion, 4.9L Main Bearing Thump in Cadillac Engine Technical Discussion; I got a 84'coupe deville with a 4.1 68,000 original miles on it, it has always been real sluggish, is ...
  1. #16
    79malibuonblocks is offline Cadillac Owners Member
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    Re: 4.9L Main Bearing Thump

    I got a 84'coupe deville with a 4.1 68,000 original miles on it, it has always been real sluggish, is this normal? Seems like the tranny slow going gear to gear, almost like its slipping. But no mechanical problems with the motor, x-cept a receipt I found for a rocker stud replacement back in like 1992.

  2. #17
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 4.9L Main Bearing Thump

    Quote Originally Posted by 79malibuonblocks View Post
    I got a 84'coupe deville with a 4.1 68,000 original miles on it, it has always been real sluggish, is this normal? Seems like the tranny slow going gear to gear, almost like its slipping. But no mechanical problems with the motor, x-cept a receipt I found for a rocker stud replacement back in like 1992.
    The 4.1 was never known for performance. Sluggish is being kind.

  3. #18
    79malibuonblocks is offline Cadillac Owners Member
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    Re: 4.9L Main Bearing Thump

    Quote Originally Posted by Ranger View Post
    The 4.1 was never known for performance. Sluggish is being kind.
    Well, I feel better, i suppose. I definately know its a highway cruiser. Anything I can do to improve the performance? I already did a new fuel pump, filter, air filter, plugs, wires ,cap, rotor button.

  4. #19
    quins90lac's Avatar
    quins90lac is offline Cadillac Owners Enthusiast
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    Re: 4.9L Main Bearing Thump

    Quote Originally Posted by 79malibuonblocks View Post
    I got a 84'coupe deville with a 4.1 68,000 original miles on it, it has always been real sluggish, is this normal? Seems like the tranny slow going gear to gear, almost like its slipping. But no mechanical problems with the motor, x-cept a receipt I found for a rocker stud replacement back in like 1992.
    if it feals like its slipping or having soft shifts you might want to try replacing the vac modulator on the trans. it like under 20 if it is that then that 20 just saved you a trip to the shop

  5. #20
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: 4.9L Main Bearing Thump

    Quote Originally Posted by 79malibuonblocks View Post
    Well, I feel better, i suppose. I definately know its a highway cruiser. Anything I can do to improve the performance? I already did a new fuel pump, filter, air filter, plugs, wires ,cap, rotor button.
    Nothing I know of. I improved mine by trading it for a '92 with a 4.9.

  6. #21
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 4.9L Main Bearing Thump

    If you replace the vacuum modulator with an adjustable type (a screw inside the vacuum hose fitting), and if it is sort of "sliding into gear" during shifts, turn the adjusting screw in (clock-wise) a couple turns and try it. It may take more.
    Seems like the plunger in the modulator takes up the slack on a worn transmission to some degree.

    If the engine is really sluggish, you may want to check ignition timing. It may be running a bit retarded (late)

    Mine is no power house, but it's quite responsive to the throttle.

  7. #22
    79malibuonblocks is offline Cadillac Owners Member
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    Re: 4.9L Main Bearing Thump

    timing is right on, 10btdc i believe. Might check out that modulator

  8. #23
    bcpape is offline Cadillac Owners Member
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    Re: 4.9L Main Bearing Thump

    Hello all- Been a while since I've been here. Over the last few weeks I have continued to talk to people and I still get a different opinion with just about everyone I talk to. I have a friend who lives Cadillacs. It's actually his business as well and his take is this. The bearing thump is most prevalent in the 4.9's. I does occur in the 4.5's if it has not been well maintained. The added power of the 4.9 and added weight of the later models seemed to have made the problem more noticeable, which is why more 4.5's don't seem to have it as bad. He claims that the bearing swap is a good idea, but the noise is indeed somewhat harmless. It can be done with the engine in the car, HOWEVER I learned that removing the cross-over exhaust pipe which runs directly under the pan is a major pain. Expect to have to cut some pipe. I attempted to do this, however when I could not get the pipe off, I gave up for the day. Like MacArthur, I shall return! As for the bearings, they are available from Rock Auto and are not costly. They are .026 UNDERSIZED, NOT OVERSIZED. Oversized would only make the problem worse. My friend also recommends changing the rod bearings while we are in there. They are also available in .026 undersized. I am also going to replace the oil pump, even though a high volume is not made for this engine.

    As for the origin of this problem, it is indeed a design flaw. Cadillac is the only division blessed with its own engine line. If you all notice, they even sound different with a more throaty sound than other small blocks. This problem is the result of the tension on the surpentive belt coupled with the power stoke of the the two end cylinders, tends to increase the oil clearance on the #1 main bearing. Not to the point of being a serious problem, but just enough to make the annoying, infamous bearing thump.

    The newest problems that I have encountered are the radiator. The plastic side tank (bad idea!) cracked and I have found a heavy duty, two row, metal tank replacement unit on eBay for anyone who might be interested. These cars seemed to run hotter than I like. No wonder being that they have a single tube radiator. I am also changing the injectors as I have one that is failing. I am going to the new design Bosch injector. It has 4 holes instead of 5, which I am told will enable me to run regular unleaded without knocking.

    Stay tuned.

  9. #24
    Sevillian273's Avatar
    Sevillian273 is offline Cadillac Owners Connoisseur
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    Re: 4.9L Main Bearing Thump

    Id like to know where you got the radiator if you dont mind.

    I dont see how the spray pattern will effect whether or not it pings. You might wanna look into that.

  10. #25
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 4.9L Main Bearing Thump

    Since I fixed my oil pump problem, my 4.1 is thumping happily down the road, just as usual The front main bearing appears to be accessable (sp) with the pan off, bit I was in no mood to fool with it this time around.

  11. #26
    83CADMAN's Avatar
    83CADMAN is offline Cadillac Owners Fanatic
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    Re: 4.9L Main Bearing Thump

    Quote Originally Posted by 90BeigeElDorado View Post
    I would take a 90+ 4.x engine over a Northstar any day of the week. HaHa. Seriously, I think that these are really good engines(88's and up) as long as they are properly maintained. Heck, I think that their are people on this forum with later model 4.1's that have well over 150K on them.
    My 90 Seville 4.5 has 297k and runs thumping great. Sadly my 94 N* has 114k and is a Victim of HG syndrome.

  12. #27
    steelybill is offline Cadillac Owners Enthusiast
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    Re: 4.9L Main Bearing Thump

    I don't think I ever want a Northstar powered car. I always picture a 4.1 thru a 4.9 with overhead cams. Enough problems without dealing with OHCs.
    All the little cars out there these days with 4 valves per cylinder will just get junked when engine problems occur because of the expensive repairs and labor intensive fixes. I like my old Caddy, but I'm of the opinion that front wheel drive was just a cheaper way for automakers to produce cars, and the same goes for unibody designs. A little rust, and they are junk.

    It seems to me that the 500 was the last good Caddy manufactured engine.

  13. #28
    SOUTHWESTCADILLAC is offline Cadillac Owners Member
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    Re: 4.9L Main Bearing Thump

    Hmm... Thats funny the fix as ya'll call it Fixes them here at my business?? I use the 3545719 front bearing on number one main journal. Now this bearing is discontinued but the I a bunch in stock that arent for sale. However I believe you can get the same bearing aftermarket thats made for a STANDARD POLISHED crank at machine shop...but only use the front one out of the set. Maybe that Dealership didnt want to do it because of the lack of parts?

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