1985 Fleetwood FWD 4100
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HT4100 4.1, 4.5, 4.9 Discussion, 1985 Fleetwood FWD 4100 in Cadillac Engine Technical Discussion; Hello all I have been reading a lot about the HT 4100. I have recently bought a 1985 Fleetwood FWD ...
  1. #1
    I4GET2 is offline Cadillac Owners Member
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    1985 Fleetwood FWD 4100

    Hello all I have been reading a lot about the HT 4100. I have recently bought a 1985 Fleetwood FWD Sideway sitting HT 4100 for $500.00 The car is not in too bad of shape but I do have concerns. I replaced the Water Pump recently and found I do need to add the stop leak. Thanks for that info as I am one who doesnt read the stickers under the hood. Anyways my question is this. The car is making knocking noises Im assuming it is from the cam wear down. Im wondering can I get a cam from a 4.5 and install on this 4100 engine since they were basicly the same. Im wondering will that fix the cam issue. Any advise on this will be greatly appreciated.

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    Edahall's Avatar
    Edahall is offline Cadillac Owners Enthusiast
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    Re: 1985 Fleetwood FWD 4100

    THe 4.5L uses a roller cam.

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    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
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    Re: 1985 Fleetwood FWD 4100

    Quote Originally Posted by I4GET2
    Hello all I have been reading a lot about the HT 4100. I have recently bought a 1985 Fleetwood FWD Sideway sitting HT 4100 for $500.00 The car is not in too bad of shape but I do have concerns. I replaced the Water Pump recently and found I do need to add the stop leak. Thanks for that info as I am one who doesnt read the stickers under the hood. Anyways my question is this. The car is making knocking noises Im assuming it is from the cam wear down. Im wondering can I get a cam from a 4.5 and install on this 4100 engine since they were basicly the same. Im wondering will that fix the cam issue. Any advise on this will be greatly appreciated.
    You cannot use a 4.5 cam. It is a roller cam and needs roller lifters which willnot work in the 4.1.

    I would not expect a worn cam to make any noise per se. If the engine runs good then I would not expect a cam at all.

    That year of 4.1 could have some lower end noise...a deep rhythmic main bearing "thump" that was not too uncommon at high miles. It is perfectly "normal" in a sense for a 4.1 with a lot of miles and years. It is casued by the serpentine belt pulling the crank upwards all the time and the compression loads pushing it down...so the clearance in the front main bearing causes it to "thump". It will not hurt anything at all and is just an annoyance. The engine will run forever like that. If you want to check and see if that is what the noise is then just take the serpentine belt off and start the engine and run it for awhile and see if the noise disappears. If the serpentine belt removal eliminates the noise temporarily then it is the main bearing thump.

    For a $500 car I would leave it alone and/or just try some Delo or Delvac HD 15W40 oil in the engine as the slightly heavier oil will help the noise a bit. IF you really want to fix it you can go to the Cad dealer and buy special service front main bearings that have reduced clearance that will elimate the noise. They can be installed by removing the pan in the car without pulling the engine. Personally, I would just drive it and leave it alone as the costs of the bearings and the service work would be more than the car is likely worth...but if you can do it yourself it would be a positive fix.

    Definitely keep the coolant supplement up to snuff in the cooling system as the intake gaskets or the head gaskets can seep coolant into the oil over time causing the heavy cam wear you describe. Replace the coolant frequently and always put a fresh dose of the GM coolant supplement in the sytem.

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