Pilot Bushing crank

Discussion in 'U-shift em' started by Buickcub, Jul 25, 2021.

  1. boe

    boe Platinum Level Contributor

    always an exciting topic. Like Jason's .003 > crank ID.
     
  2. Stg'd 2Discover

    Stg'd 2Discover Lumpty, Lumpty, Lumpty

    I did the 6 speed Tremec swap and used an oilite bushing acurately machined to be concentric and also dial indicated/corrected the bell housing. Tremec's don't tolerate much offset so having that input shaft in line is important.

    The pic shows a special micrometer that I used for determining the wall thickness of the oilite bronze bushing. This new bushing's wall thickness varied when measured in 4 spots, but was corrected when machining the new OD to fit the crank. I went with a .001 interference fit bushing to crank . ANSI class V standards recommend a min of .0004 to a max of .002 oversize for pressfit in this diameter range.

    correc IMG_1585.JPG IMG_1586.JPG
     
  3. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    That is helpful info for me, since I am in the middle of a similar swap.
    Question: I don't have one of those special micrometers--or any micrometer, actually. But I have a caliper. How acceptable would it be to get those measurements using a caliper? Accurate enough? Or not good enough? thanks
     
  4. Stg'd 2Discover

    Stg'd 2Discover Lumpty, Lumpty, Lumpty

    By measuring the wall thickness of the bushing, I just wanted to alert to everyone that these bushing are not always perfectly concentric as purchased and can be a source of alignment error. If you remachine the OD of the pilot bushing to fit the crank, reference the bushing's center hole. This should be done at least on a lathe between centers or on some kind of holding tool that accurately references the center hole. Don't hold the bushing in a hand drill and file the OD to fit.... Thats a real hit or miss.

    I don't expect many to have special tool & die shop instruments and machines like I have. You can probably use a vernier caliper for pre determining your crank's pilot hole size to some degree. Try to measure it many times and when you get some repeatability use that number, but remember the more precise the measuring instrument the more accurate the measurement will be. If you want acuracy to the 1 thousand's of an inch, your measuring device should be able to read to the 10 thousands of an inch.
     
    Last edited: Jul 29, 2021
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  5. FJM568

    FJM568 Well-Known Member

    What kind of clearance should you have in the bushing hole to the input shaft after installation? i.e., how much bigger is the hole compared to the shaft?
     
  6. Stg'd 2Discover

    Stg'd 2Discover Lumpty, Lumpty, Lumpty

    2-3 thousandths is commonly recommended between input shaft to bushing.
     
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  7. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    Okay, I just pulled my old bushing out of my engine's flywheel...with my fingers. Should it be that loose? I didn't need to use the "hammer in some grease or a slice of bread" hack. I also stuck it on the input shaft of my brand new TKX, and it slid right on with about the same amount of ID slop as the OD slop in the flywheel. E.g., a nice, slide-y fit but not really enough play to wiggle it. I will attempt to measure the actual gaps, but I'm hoping that a press-fit or "hammer it in" tightness isn't necessary. Thanks for any wisdom you can share.
     
  8. TrunkMonkey

    TrunkMonkey Well-Known Member

    It needs to be press fit, and the pilot needs .002 to .003 clearance.
    You do not want the pilot being "grabbed" by the bushing, or you will have clashing and front case bearing/input shaft can be damaged from the forces transmitted from the crank.

    And if the bearing is not a tight fit to the crank, it can wobble and create a "flutter" and that can also damage the input shaft/bearing.
     
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  9. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    Thanks. A tight fit was what I expected to find, so I was surprised when the bushing came out so easily. When I installed it, 35 years (and 100 miles) ago, I don't remember it going in that easy. I probably used the ol' "backwards socket and deadblow hammer" method to install it.

    So how did it get so loose after such low engine time? The engine is barely broken in, the old pressure plate and clutch look almost new. The bushing doesn't seem to have been spinning in the crank hole--the OD surface looks new. Maybe when the engine got up to running temperature, heat expansion made it have a snug fit?

    Anyway, I guess I need to find a new pilot bushing that is a few thousandths larger O.D. Hope they are in stock somewhere.
     
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  10. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    In case it will be useful to anyone, I will try to post some pics of what I found after I removed my bell housing & clutch:
     

    Attached Files:

  11. TrunkMonkey

    TrunkMonkey Well-Known Member

    upload_2021-8-8_15-34-12.png

    Is the red iron (crank material) or is it brass?

    Is the blue grease?
     
  12. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    Good questions. I will crawl back under my car and investigate, and report back later today. :)
     
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  13. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    Since I have the bushing out of the car, I cleaned it off using a Scotch Brite, and it seems pretty unscarred except for a gouge on the face of the tranny side, and some scuffing on the ID where you'd expect to see it from the pilot shaft. I don't know what that stuff was that you circled in red. Gonna go check out the crank now to see what the blue was.
     

    Attached Files:

  14. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    I dunno, TrunkMonkey. What looked like metal shavings turned out to be hardened grease, from what I could tell. Does the end of the crank look funny to you, like it got damaged at some point? Here is it after cleaning it out a little:
     

    Attached Files:

  15. TrunkMonkey

    TrunkMonkey Well-Known Member

    That looks fine. It should not have any grease in there.

    That is what I was seeing, but the "ragged" edges looked like the end of a brass drift punch that has "mushroomed" and I wanted to rule out some odd brass insert in the crank boss.

    Clean that with brake cleaner and a wooden dowel and a rag to get it clean and dry before you put the bushing back in.

    If it were me, I would buy a new bushing, they are relatively low cost and the oilite type can have the pores clogged with grease or oil and fail (sticking or "grabbing" the pilot on the input shaft), leading to clashing gear changes.
     
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  16. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    Excellent, thanks! I just checked the new bushing that came with my new McLeod clutch, and it is bigger than the old one that came with my old clutch. The new one measures 1.096, compared to the 1.075 of the old one. So there ain't no way the new one is gonna be loose in the crank-hole. I may be turning it down some.

    One more question: Once the crank-hole (sounds like a cuss word) has been degreased, should the bushing be a totally dry fit, with nothing at all applied to the hole? I.e., no antiseize, etc., because applying anything would plug the bushing pores ?

    Thanks again for the advice.
     
  17. TrunkMonkey

    TrunkMonkey Well-Known Member

    Correct. It will go in dry as long as it is turned for a proper press fit.
    Use a puller/pusher to drive it in, it will center and "press" it evenly and square to the bore.

    Do not press it in until it bottoms out. It needs to be near flush, as you are supporting the pilot closer the the transmission and not closer to the tip of the pilot shaft.

    put the bushing an a baggie or wrap in Saran wrap and stick it in the freezer overnite.
    You want about .0005 more on the bearing OD than the ID of the bore in the crank.

    Use a steering wheel type puller and a socket to drive it in. You can use a deadblow hammer, but it does not take much to damage the bearing and have it deform.

    Mic the ID of the pilot hole, and ensure it did not "close up" when installed. If the transmission flange does not mate completely and without gap when you mate the transmission, do not pull it in place with bolts.
    You risk breaking ears, or jamming the pilot shaft into the bearing.

    Some may think it is "overkill", but the small amount of time spent doing it right, vs having a problem with shifting, or having to do it over, is worth that effort.
     
  18. 69GS430/TKX

    69GS430/TKX Silver Level contributor

    Great advice, I appreciate the cautions that will prevent messing it up. The instructions that Tremec sends out with their trannies doesn't cover bushing prep. The instructions that Bowler included do mention the clearance tolerances for the bushing, but none of the details you have provided.

    One interesting thing Bowler mentioned is that they have seen transmissions that were wrecked because the installer forgot to even put a bushing in!
     
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  19. Buickcub

    Buickcub Well-Known Member

    The existing hole in the automatic crank is tapered at the lead in. is was not a precisely machined hole in my crank
     
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  20. IDOXLR8

    IDOXLR8 Senior Member

    I went through this mess, take a new polit bushing with the crankshaft to a quality machine shop!
     
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