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Thrust bearing destruction and engine/trans rebuild - the solution finally - at end

Discussion in 'The Garage' started by mouse, Apr 9, 2006.

  1. mouse

    mouse 1/2 ton status

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    Due to a worn down lift, I am pulling the motor down (350). It seems that I may have excessive wear on the thrust bearing. When I went to pull the harmonic balancer, I could move the crank in/out more than I am comfortable with, so I decided to yank the whole thing and take a closer look (and to make the cam replacement a bit easier).

    The engine has about 4000 miles since being rebuilt. The crank was turned 10/10.

    I plan to check thrust tolerances with a feeler gauge. Is there anything else I can do? What should I look for?
     
    Last edited: May 25, 2006
  2. 79Jimmy

    79Jimmy 1/2 ton status

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    IIRC crankshaft endplay should be .005" - .007" Anything over .010" is excessive. I would check the rod side clearence while your at it.

    James
     
  3. projectcop

    projectcop Registered Member

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    Mouse;
    If you dont find a problem in the motor that would have caused a premature thrust bearing failure, check the trans. If it is an auto, check to make sure the convertor is not swelling and pushing the crank forward. Also, make sure the flexplate is installed correctly. If it is a manual, make sure the clutch is adjusted correctly. If it is adjusted wrong, it could also be pushing the crank forward thus wiping out the thrust bearing. Please do not take this the wrong way, but if it is a manual, do you drive around with your foot on the clutch pedal? That can do it also.
    In almost ten years of building engines in a shop in sanfrancisco, the only time I saw a SB chevy wipe a thrust bearing was when an auto convertor swelled or was installed incorrectly (not all the way in the trans).
    George
     
  4. diesel4me

    diesel4me 1 ton status Premium Member

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    loose cranks....

    The 79 400 SB I just sold a few weeks ago was in my 74 K20 since 1995...when I pulled the motor to save it for resale or future use,I noticed it had a lot of "end play" in the crank...you could pull the crank in/out about 1/8" at least!!:eek1: ..it may have ALWAYS had that play there,I never noticed it during the swap from its original Suburban into my K20..it always ran well,never had any bottom end noises ,even upon cold starts..

    I did use the truck mostly to plow though,and haul heavy loads once in a while..it could be the torque converter balloned and wore the thrust surfaces on the bearing ,and crank I guess..I've heard a blocked trans cooler line will cause the converter to push the crank forward and do the same thing..anyhow,I sold it for 150 bucks as a "rebuildable core"..but I was suprised to see that end play,when it ran so decent and never knocked..probably was that way long before I got it...:doah:

    My friend had a 63 T-Bird with a 390 V8,its crank used to float in and out 1/2" while idling,and the oil light would come on every time you took a corner!..:eek1: it threw all the fan belts off twice,but he managed to get 2 years use out of that motor before installing a fresh one he'd found to replace it..
    I thought it would seize up every time I got in it,and have to walk home..

    I think I remember seeing listing for "oversized" thrust bearings in the Sealed Power parts books,or Fedral-Mogul catolog..they have thicker flanges to make up for the crank being resurfaced where it rides..:crazy:
     
  5. mouse

    mouse 1/2 ton status

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    Its an auto. I'll get a ggod look at the converter. I planned on replacing the front trans seal while the engine was out anyways. I've heard of ballooned converters in diesels but never on SBC before, but I guess its the same principle. Is there anything to look for, or will it be apparent? The truck rarely sees over 3000 rpm.

    projectcop, tell me more about the flexplate, and how that could cause the problem. Last time I had the motor out, I put a new flexplate on it. I am pretty sure it can only go on one way. The old one was beat to ^%$ and looked like someone installed it with a hammer at one time. It was a tight fit coming off the back of the crank.

    I should have it out and the problem figured out sometime this week. Now, I have to find a cam. I'll be calling Comp cams today.
     
  6. mouse

    mouse 1/2 ton status

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    Got the engine out and crank end play was at .040. Way too much, so out came everything. The rear of #5 bearing was down to the copper and the crank surface is chewed up. It will be going to the machine shop for their opinion tomorrow.

    The torque converter looks fine, as does the new flexplate thats on it. The rest of the bearings looked good. One small groove in the #6 connecting rod bearing, probably from the cam/lifter destruction.

    I noticed that only the upper #5 main bearing had an oiling hole, and the bottom did not although the bearing cap has what looks like a oiling hole. Any concerns here?

    Any ideas?
     
  7. mouse

    mouse 1/2 ton status

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    Update:

    Machinist said he could weld material into the thrust bearing area on the crank and turn it another .010 for a cost of $90 - $100, but that it would harden the #5 bearing surface a bit on the crank. He told me they do this for Ford 302's all the time.

    I didn't like the idea of a "welded/repaired" crank so asked him for their price on an Eagle cast replacement. Surprisingly he quoted me $192, only $3 more than Summit, before shipping! So, I ordered the Eagle. I will probably have to balance the rotating assembly for another $175, unless the new crank is very close. Plus, because they can re-sell my crank, they will give me $40 credit for it.

    Back to the problem. After discussing it with the machinist and reepair guys they all said it HAS to be the trans. Either the cooler/cooler lines are blocked causing the converter to apply forward pressure on the crank, or the pump is going out causing the problem. I can't seem to understand the pump scenario...

    Fortunately I have acquired a good running trans/TC spare of exactly what I am running yesterday (not a day too soon). I will hit the cooler lines with compressed air and see what happens, and just swap trans/TC's. Before swapping the new trans will get new seals, fluid and filter.

    This project is growing out of control!:eek1:
     
  8. R77K10

    R77K10 Banned

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    yeah thrust bearing play can be bad thing

    also if someone ever beat the balancer on with a BFH then well........ run away fast

    good luck
     
  9. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    There are several reasons that a thrust bearing fails. The most common failure is due to a ballooning torque convertor, next is a reground crank and the crank grinder not getting a smooth enough surface on the thrust areas of the crank, and also a bad ground can cause it. There is really no way of checking for a ballooning convertor so if it is even a question just replace the convertor. Make sure that there aren't any plugged or pinched tranny lines as well.
     
  10. projectcop

    projectcop Registered Member

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    Mouse;
    sorry it took so long to reply. The flexplate CAN be bolted on bass akwards. I have seen people put them on like that (flipped backwards). Of course if this was the case, the starter would probably not have worked. by the way, the flexplate is supposed to be a tight fit around the end of the crank.
    One more thing, if you have the wrong flexplate on it, say a 400 flexplate on a 350, or vice-versa; the motor will have a vibration in it that could wipe out the thrust bearing. The 350 plate has a balancing wieght on it, the 400 does not.
    george
     
  11. mouse

    mouse 1/2 ton status

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    I went and took a quick look at the flex plate. There are no weights on it. I thought the 400 (externally balanced) would have weights, where the 350 would not. I will have to double check the flex plate.
     
  12. mouse

    mouse 1/2 ton status

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    While the balancer has been beat on in the past, since the re-grind during last years rebuild, I have been the only one to install it, and I only use a balancer installation tool (not the BFH type, the bearing type).
     
  13. mouse

    mouse 1/2 ton status

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  14. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    All SBC's up until 1985 were internally balanced with the exception of the SBC 400 which is externally balanced and has a welded on weight on the flex plate. Starting in 1986 with the outcome of the 1 piece rear main seal engines GM started externally balancing the rear of the engine only so there will be a welded on weight on those engines as well but that plexplate will not bolt up to the earlier engines due to a bolt circle change as well.
     
  15. mouse

    mouse 1/2 ton status

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    Thanks Scott. Thats what I thought, but I want to triple check everything so I don't have to replace a crank again! I've got another trans to go into the truck, so hopefully that will cover all the bases: new crank, new bearings, new (different) trans/TC, and hit the trans cooler lines with compressed air.
     
  16. mouse

    mouse 1/2 ton status

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    Another update.

    Called a trans shop. These guys were highly recommended by a couple of club members, so I gave em a call. I asked how the thrust bearing could go out. I spoke with an old fella, and according to him, in his many years of rebuilding trans, he has never seen a TH350 cause a thrust bearing problem. He said he seen a few TH400's do it behind a 454 in a motor home, but not a 350.

    He made a good point that the new motor only had 3-4000 miles, how come when I tore down the motor before the rebuild last year that the old thrust bearing looked so good? The trans all of a sudden crapped out? He told me to double check the cooler and lines, but other than that he would run the trans thats in the truck. He basically turned down a chance to rebuild my trans, because he was confident it is good.

    What was his alternative theory for the destruction? He asked me did I have the crank turned when I rebuilt the motor. He wasn't surprised I said yes. Apparently they have seen many people in the past couple of years who have had a thrust bearing go out on a recently rebuilt motor. The only thing in common...turned crankshafts.

    He said "the machinist told you the tranny destroyed the motor. Well, I'm the transmission guy, and I'm telling you the machinist destroyed your motor." Basically he is "99%" sure that there are problems with the machinists turning cranks here in our little town. He agreed that me buying a new Eagle crank should cure the problem.

    I've got some real concerns over the machine shop I've used now. I think I will only buy the crank from them, and start using someone else for machine work. Even if that means out of town.
     
  17. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    I did mention that in my reply to you. That is also why i high lighted what i did. :thumb:
     
  18. projectcop

    projectcop Registered Member

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    Mouse;
    Well; you are getting a little closer to a resolution to your problem. I refuse to speak badly of someones machine work unless I have seen it myself, but after hearing what your trans guy has said about other crankshafts he has seen from around there, I would suggest taking your problem-child crank to another machine shop and just ask them to check it out. Do not tell them what you suspect; just ask them what went wrong with it. Let them tell you what went wrong.
    By the way, as long as you are going to blow out those lines; why not check the actual cooler also? If you are still using the stock one in the end of the radiator, now might be a good time to add an extra cooler to your truck. An automatic transmissions biggest enemy is heat. The cooler you keep it, the longer it will last.
    George
     
  19. mouse

    mouse 1/2 ton status

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    Thanks for the replies.

    I guess I should add some more info. I have bought an Eagle cast crank (probably a week or so before it comes in), and traded the old crank in - they gave me $40 for it. I really feel that a new crank will prevent any "machinist" problems. The machine shop gave me an option to repair it by welding in new material and then turning it again...doesn't sound like a good answer to me after recent events, so I just cut my losses and am headed forward.

    I do have a rather large, aftermarket cooler on the truck. I will check the lines and both the aftermarket and stock coolers today. If I didn't live in a place that got cold, I would consider only using the stock one, but alas Montana gets very cold in the winter time.

    I bought the new crank from the shop that did all the machine work previously. They gave me a good price on the crank, but the rest of the parts quote are high.

    They want $74 for rod bearings, $28 for mains, and $50 for head gaskets. I called Eagle directly to find out why the rod bearings were so high and what were the bearings they recommended. They told me a "p" bearing and gave me clevite part numbers. A quick check at Summit shows I can get the recommended rod bearings (a complete set) for $20, mains for $19.95, and heade gaskets around $30. Quit a difference!

    The bearings the shop quoted for me are for a race engine, and actually list NASCAR on the specs. I'm done working with this shop after the crank comes in.
     
  20. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Even with a new craqnk it is recommended to have it checked for size and straightness. Depending on how the crank has been stored it can bend.
     

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