rocker arm pivot support
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HT4100 4.1, 4.5, 4.9 Discussion, rocker arm pivot support in Cadillac Engine Technical Discussion; Hello All, About a week ago my 85 Eldo started to idle rough. It had a miss. Changed the plugs, ...
  1. #1
    rcirobin is offline Cadillac Owners Member
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    rocker arm pivot support

    Hello All, About a week ago my 85 Eldo started to idle rough. It had a miss.
    Changed the plugs, wires cap and rotor, the idle was still rough. Had code 30, ISC problem, Took off the drivers side valve cover, found the rocker arm pivot support completely broken over the #5 cylinder. The rocker arms for that cylinder were just sitting there. The funny thing is the engine really didn't make any strange knocking noise, and when I was on the highway it really wasn't that bad. I mean you could feel the miss but it got up to 55 mph without much trouble. It never backfired or stalled. My question is was any damage done to the engine. How does the cylinder expel the pressure in it if neither of the valves open? Do you think if I replace the rocker arm pivot support I might have a chance of the engine being OK? The engine has been OK up to this point. It has 141,000 miles on it. Thank you, Rob

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    DFBonnett is offline Cadillac Owners Fanatic
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    Re: rocker arm pivot support

    Quote Originally Posted by rcirobin
    Hello All, About a week ago my 85 Eldo started to idle rough. It had a miss.
    Changed the plugs, wires cap and rotor, the idle was still rough. Had code 30, ISC problem, Took off the drivers side valve cover, found the rocker arm pivot support completely broken over the #5 cylinder. The rocker arms for that cylinder were just sitting there. The funny thing is the engine really didn't make any strange knocking noise, and when I was on the highway it really wasn't that bad. I mean you could feel the miss but it got up to 55 mph without much trouble. It never backfired or stalled. My question is was any damage done to the engine. How does the cylinder expel the pressure in it if neither of the valves open? Do you think if I replace the rocker arm pivot support I might have a chance of the engine being OK? The engine has been OK up to this point. It has 141,000 miles on it. Thank you, Rob
    You might be OK in that the engine seems to run well in spite of the apparent damage. Pull the plug and see if it looks like anything hit it. Price out the parts and make your decision. Based on your description it seems like it is worth the gamble.
    FWIW
    YMMV
    DFB

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    Re: rocker arm pivot support

    I HADE THE SAME PROBLEM....MY 83 COUPE DE VILLE WAS STARTING TO MAKE A TAPPING SOUND...THOUGHT IT WAS A STUCK LIFTER...

    ENDED UP TAKING OFF THE VALVE COVER TO FIND BROKEN ROCKER PIVOT BROKEN..AFTER TAKING IT OFF I NOTICED THE ROCKER ARM SUPPORT WAS BROKEN IN HALF...CHANGED THE BROKEN STUFF...AND CAR STILL RUNS SMOOTH...



    THE WONDERFUL WORLD OF 4100'S

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    rcirobin is offline Cadillac Owners Member
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    Re: rocker arm pivot support

    Thanks for for your input guys. I just ordered the part at the local dealer, it only cost twenty-five dollars. I just started it up to move it, it's cold here. Started just fine. I'll let you know how it goes. Thanks again!....Rob

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    Re: rocker arm pivot support

    If it just snapped the rocker arm pivot it should be fine.

    When you get the part DO NOT be tempted to try and put the bolts in the pivots (they are paired together) and pull them down onto the rocker arm support bar. You will likely break the new pivot or crack it so that it breaks later and/or strip the bolt holes in the rocker arm support bar.

    The correct way to install it is to take the whole bar loose by removing the four small bolts and then the 5 large nuts that hold the rocker arm support bar to the stud headed head bolts. Loosen the 5 bolts in sequence a couple of turns at a time to evenly unload the bar. Install the new pivots into the rocker arms and install onto the rocker arm support bar. Then reinstall the entire bar/rocker arm assembly by tightening those 5 nuts sequentially a couple of turns at a time to evenly pull the bar down. This is important.

    When the bar is off you need to also make sure that the pushrods for the broken pivots are correctly seated into the lifters down in the valley. I assume the two pushrods were still there...?? You can pull them up (they are just loose pieces) and then stick them back into the lifters. IF the pivot broke and the rocker arms were not restraining the pushrods then they could have popped out of the lifters and they need to be installed or at least checked to make sure that they are in place correctly.

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    rcirobin is offline Cadillac Owners Member
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    Re: rocker arm pivot support

    Hello bbob, Yes, the pushrods are still in place. I will follow your advice to the letter. Thank you very much for your help....Rob

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    Re: rocker arm pivot support

    GOOD LUCK

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    Re: rocker arm pivot support

    BTW....the cylinder doesn't need to "expel the pressure". If both valves are inoperative and closed all the time the cylinder acts like an air spring. It compresses and then pushes the piston back down returning almost all the energy it took to compress what was in the cylinder. This is the fundamental operation of the displacement on demand or the V-8-6-4 engine of 1981. The DOD works by closing both valves and leaving them closed by disabling the valve gear for that cylinder. It will not hurt a thing. The DOD engines run for thousands of miles with both valves shut.



    If you have had a chance to look at the parts....what broke?? If the bolts pull out of the rocker arm support bar then the holes in the bar are damaged and will need to be repaired with a timesert ...or the entire rocker arm support bar will need to be replaced and all the rocker arms transfered to the new bar. If the pivot broke and allowed the bolts to just loosen then the bar may be ok but many times the bolts loosen part way then yank the remaining threads out damageing the bar. If the bar itself has any threads missing it will need to be repaired/replaced. If the bolts are broken then you need to get new OEM bolts as those are special thread rolling bolts that form their own threads into the bar.... If you tap the bar and use generic bolts locktite them in place. In other words, you may need to replace more than just the pivots for that set of valves.

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    Re: rocker arm pivot support

    curious question bbob , if memeory serves this is the 6th failure here on the boards of the rocker arm support on the ht4100 , 4.5 ,4.9 . im starting to think this is a common problem . any reasons ? like perhaps the engines getting run too hard and turning to many rpm for too long of a time ?

    would it be wise for some of us than can afford it to go thru the engine and replace all the supports at a certain milage interval ? or is this something that happens to people who are too hard on the engine(no offense guys) ?

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    Re: rocker arm pivot support

    Hard to say.... The rocker pivots and rocker arm support bar is obviously loaded fairly heavily and if something is not right it might eventually fail. On the one hand I would say that the rocker arm/support bar/pivot interface is the weak link in the valve train...but that is probably true of most any pushrod engine. Not too uncommon to hear of a rocker arm ball burning up, a rocker arm pivot nut coming loose, etc... on other engines with high miles. I think that it is just the nature of higher mileage engines. We have no way of knowing what might have been done to those engines earlier, either. If the rocker arm pivots were removed from the bar individually before removing the entire bar it is very easy to damage the pivot/bolt hole/bar. Possibly that was done at an earlier service and the part just now showed the failure from the previous mis-assembly. I would not go into the engine and just replace the rocker arms/support bars/pivots as preventative maintenance. Plus, this is like a lot of other things....the part breaks so the owner looks up the forum for help. I have seen those parts go 300,000 miles and further on taxi cabs so I don't have any reason to suspect hard usage or anything causes the problem.

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    Re: rocker arm pivot support

    ahh , thankx for the imput !

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    rcirobin is offline Cadillac Owners Member
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    Re: rocker arm pivot support

    Hello bbob, It's the rocker arm support bar that is broken in two places above the #5 cylinder. The pivot and the two rocker arms are still attached to the broken portion of the rocker arm support bar. It is not near any mounting holes. I would think the bar had some sort of stress crack. I will replace the entire bar and transfer the rocker arms from the old bar as per your advice.

    This motor has been very good to me. The car has ample power for me and is great on the highway. I get 16.4 mpg. I'm happy with that. I never push it. Maybe I should!

    The explanation using the V-8-6-4 engine as an example made me feel better about both valves staying closed.

    Will let everyone know what happens......Thanks.....Rob

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    Re: rocker arm pivot support

    You should be fine with the new bar. Just remember to install all the rocker arms onto the new bar on the bench. Those are all self tapping bolts so start them carefully and straight so that they set correctly into the bar. The self threading bolts actually roll their own threads which are much stronger than cut threads and act as a strong thread locking method for holding the bolts secure. Look at the end of the bolt threads and you can see the tri-lobular pattern on the bolts along with the pointed end that forms the threads in the aluminum bar. I don't remember the torque of the bolts off hand. Find out what they are from the service manual or if someone has one they can tell you. You want to start the bolts, run them down and torque them carefully. Try to do it in one smooth motion running the bolts down to torque in one motion. If you run them down and then torque, loosen before pulling to the corrcect torque so that you are measuring a dynamic torque as the bolt seats. This is important as the bolt does not go thru the bar so it is still rolling threads while it comes to torque. This locks the bolt from loosening but it can cause a misleading torque reading if you partially tighten them and then put the torque wrench on them as the torque to bread the bolt away will be too great and the bolt can be a little loose and still register torque. Run them down all the way, loosen and pull to torque smoothly while it is still turning.

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    rcirobin is offline Cadillac Owners Member
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    Talking Re: rocker arm pivot support

    I replaced the rocker arm pivot support bar today. I followed the advice I was given, all went well. The car runs as good as ever! Thanks to bbob and all who gave their advice. I really appreciate the help....Rob

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    willone is offline Cadillac Owners Member
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    Re: rocker arm pivot support

    thanks i need to know pivot suppurt number, and store too buy them, is 4.1lt engine thank you again,

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