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HT4100 engine with crank knock 6K miles

Home Forums Stay Dirty Lounge Service and Repair Questions Answered Here HT4100 engine with crank knock 6K miles

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  • #873336
    john randjohn rand

      I have a 1983 Eldorado Biarritz with 6K miles, 100% original except for fluids. I just got the car but it has been sitting since 1988. These HT4100 engines are known to have been defective from the factory with bearing issues. I have the infamous crank knock. It is very slight but I can hear it when in gear after the engine warms up. I only use Mobil 1 Full Synthetic and used 30 weight (as per the owners manual and my climate). I put in 1 bottle of Heavy Duty Lucas oil treatment and it is almost non existent. The only thing is as the engine heats up, the knock shows up slightly but only sounds like a puffing noise (almost like a hole in the exhaust). I was wondering if I put in 15W-50 and Lucas would that stop the noise all together? Or should I keep what I have in there and put in some heavy gear oil in place of a quart of oil? Please help me make this hush quiet, as there are no options of rebuilding the HT4100 because there are no longer over sized bearing available for the car. Please note when new they would just replace the engines and after the warranty they would use .10 over sized bearings, which stopped the noise, but now that is not an option. What do you suggest? Thanks for your help in advance. John

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    • #873366
      college mancollege man

        I would use the correct oil and the Lucas treatment and live with the noise if you can.
        Heavier oil does not solve the problem It masks it at best.


          Think of it this way: The noise isn’t the problem, it’s a symptom of the problem. Hiding the noise doesn’t solve the problem.

          If you can’t find the parts for a rebuild, or don’t want to do a rebuild, I believe several other GM engines will bolt into your Caddy without too many issues. I’ve read where owners would toss their problematic HTs and bolt in an Oldsmobile gasoline V8.

          john randjohn rand

            No, its a show car and can not be changed out for another engine. It will kill its value. I only want to mask the problem. I know it’s there and I don’t care, I just don’t like hearing that puffing noise. Will 15W-50 work with the Lucas work better than the 0w-30 with the Lucus? I can’t get straight 50W, as it is special racing oil and will be extremely expensive in a full synthetic. I’m just asking would changing up the viscosity and adding the Lucas make it quieter? Its pretty quiet now but in the summer when its 125*, I’m thinking it will thin out pretty fast and be louder. Please advice.

            Rick CropperRick Cropper

              Yes we run 15w50 Amsoil Dominator race oil in all of our larger oil clearance race engines.Most manufacturers of high performance engines do similar. Ford calls out 5w50 on the new Focus RS turbo. BMW runs some really heavy oil on the newer M series engines. 60 weight I think.

              It will help. Instead of Lucus though – find a Justice Brothers distributor and get the thick motor honey they sell. It’s an upgrade over the Lucus product.

              Get an oil pan heater and plug it in before you start it. Also let it idle for 15 to 20 minutes before you drive it. We do this with all built engines. Letting them normalize before putting them under a load is imperative. Also get an Amsoil oil filter for it. If it’s making metal you will want the better micron rating and the cold flow ability to avoid hitting filter bypass during startup. Closer you can get to full flow the better. Especially with thick oil.


              A toyotakarlIts me

                My first reaction to reading this post was to light the car on fire and drive it into a body of water (the Viking funeral) after having worked on these engines before… But since the car is pristine and won’t be a daily driver I don’t think you would find the humor in that…

                Its hard to believe there are still any more 4100 HT’s running. We used to joke that HT stood for “Have Two”. Meaning keep an extra engine around. In the 80’s, dealers kept dozens of these on hand in crates for their eventual replacement. The 4100HT would work well enough until they overheated then it was game over…(aluminum block engine and cast iron heads…. what could go wrong?)… Well, the differing heating and cooling rate (the ever so slight expansion and contraction) of the two materials would eventually cause head gasket failure. Then coolant would mix with oil and cause bearing failure (the knock) Most owners found out about that the hard way (when the engine overheated). And as stated ahove, an overheated HT will be quickly ruined. GM responded to the problem by recommending coolant pellets, but it just delayed the inevitable… The only defense is that if the car ever starts to run above temperature, stop operating it IMMEDIATELY and get the problem fixed.. Ensure the coolant level is always proper and check the oil frequently… Suffice it to say this engine was an engineering failure in the tradition of the 8-6-4 and the later Northstar.

                Since you want to keep it as a show car, the expression “you gotta pay if you wanna play” comes in.

                Getting bearings custom made is the proper solution if no stock bearings can be found
                .. and that will cost you some $$$… Everything is do able with enough money…

                Good luck…


                john randjohn rand

                  Well, except for the clearance issues with the crank bearings there is no issue with power or performance. I had one when brand new in 83 put 100K miles on it drove it across country towing a u haul trailer (in the summer) and never had to ever take it to a shop for repairs. I always kept the maintenance up and never thought it was ever an issue. I actually loved the car so much I waited until I could find a brand new example and I did. The cam knock isn’t bad I just want it whisper quiet. Its almost gone and I am in the car very deep. I have been offered what I’m in it for but am not selling a brand new 34 year old car. So, I just wanted an answer to my original question that if changing up oil weights would keep the sound unnoticeable. I only drive my collector cars 500 miles a year anyway.

                  john randjohn rand

                    Mobil 1 Synthetic 15W-50 and a special additive took care of any an all noise. Its like it isn’t even running. I was told run 1 quart of Marvel mystery oil in the crank case with the 15-50 and it will thin it out to 10-40 then it will have all of the extra zinc that you wont get out of the other oils.

                    john randjohn rand

                      Ok, I forgot to update everyone. Right after I asked for 800.00 I found a mechanic, ( who is now one of my best friends) and he opened up the intake and we replaced the cam, lifters, timing chain and put on a cam button. We found the noise is actually the distributer pushing the cam back and fourth and the front lobe knocks up against the engine block. We solved it by buying a cam button from a 4.9 Cadillac engine and that kept the cam from rocking back and fourth. I am using the proper 5W-30 as per the owners manual and it’s quiet as a church mouse. I’m now using the new HT-12 Vavoline green coolant, which is only sold through BMW, here in the states. It saves you from have a heat exchange issue as well as any corrosion from the dissimilar metals, so no need for the pellets. I bought used all NOS parts including a NOS water pump and it’s been perfect ever since.

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