Auto or manual crankshaft?

Discussion in 'The Bench' started by B-rock, Jan 19, 2021.

  1. B-rock

    B-rock Well-Known Member

    Wanting to verify some info. There is a strong possibility my 482 will get a TRX behind it. Or a T400 for now to keep costs down. Can you do a "dual purpose" crank? that will accept the torque converter or a pilot bearing?

    I have to assume that is the only difference in an auto or manual big block Buick engine.
     
  2. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    Same crank, but internal balance it and balancer and flexplate/flywheel. Then you can go back and forth.
     
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  3. 6455spd

    6455spd Silver Level contributor

    The only difference is a manual crankshaft has a second drilled diameter to accept a manual pilot bushing. I cut the pilot bushing itself to fit in a crankshaft that was not cut for a manual. I'm not sure how many percentage wise were drilled for a manual, but I believe it as far more than the number of manual transmissions installed. I think the number is 1.090" diameter to accept a pilot bushing (1.094"), but that number is from memory so some please correct me if so.
     
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  4. flynbuick

    flynbuick Guest

    This technique will not be satisfactory if the factory hole is not properly centered. There is a report of this happening.
     
  5. knucklebusted

    knucklebusted Well-Known Member

    Don't they also make a bearing that sits where the snout of a torque converter would go? I know they aren't optimal.

    Would a 70 455 block that has the boss tapped on the side for the clutch stud and the crank mostly drilled out (unsure, haven't measured) likely be manual capable?
     
  6. B-rock

    B-rock Well-Known Member

    Yes I am very serious, why else would I make this post? does this Question bother you?
     
  7. B-rock

    B-rock Well-Known Member

    Gahh, More money to spend on it.... it never ends. LOL
     
  8. Jim Weise

    Jim Weise EFI/DIS 482

    My opinion is that spending big bucks to put heavy metal in our 4 counterweight stock crank, for a 6000 rpm engine, is a huge waste of money at best... at worst it's a bent crank.

    There is no issue going from a flexplate to a flywheel, have both of them checked when you get your crank balance done. Also, have them fit the OD of a bronze pilot bushing to your crank. Some cranks actually have the hole drilled partially, so there is a "step" of a few thousanths, and we have had to machine the pilot bearing to fit in that step in the past,, no big deal for your machine shop,

    When the time comes to switch to the stick, just put the flywheel on, and pop in the pilot bushing.

    One other thing to keep in mind.. The Tremec transmissions are very picky about alignment.. if your machine shop has the BHJ Dowel tru equipment, have them do it.. We do that on all our engines here, and I just dialed in one with the jig plate, and it was right on the nuts..

    JW
     
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  9. B-rock

    B-rock Well-Known Member


    Jim, with my lack of knowledge of being able to explain properly to a local crank grinder what needs to be done on my stock 455 crank to make it the 482... I think I would like to ship it out to you and have the peace of mind that its done correctly. How Do I pull the trigger on this?
     
  10. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    I guess I learn something everyday, maybe I'm too conservative in my builds but I'm probably going stay safe as far as internal balance on hp motors, especially the strokers I do. Thanks for the info.
     
  11. Jim Weise

    Jim Weise EFI/DIS 482

    Just shoot me a PM.. we can work that out.

    Interesting you put it that way Gary.. I would say that I feel that it's me that is being conservative, keeping these street motors external balanced, avoiding the invasive hole drilling and welding required to add heavy metal to a stock crank to change it to internal balance. HP is not really the concern, rpm is the killer.

    I won't argue that there is not a benefit, and in certain situations, I would recommend internal balance. But experience has taught me that there is no downside to external balance, and avoiding the invasive and expensive conversion process, for NA street motors to 650 HP or so.

    Those street motors spend most of their lives at part throttle, and while needing to be strong enough to handle the occasional trip to the strip or blast down a county road, they don't need to be built like race engines.

    It's economics.. cost vs need vs benefit

    If I were building an iron race motor from scratch, where the customer has to buy everything, then if I could not talk the guy into spending an extra 1500 or so to buy the Molnar Tech billet crank, I would suggest the internal balance conversion on a stock crank. Explain to him the benefits and costs, let him decide.

    Different application altogether.. and that engine spends enough time at rpm's past 6000, that we need to worry about load on number 4 main bearing, caused by the balance weight swinging around on the flex plate.

    But even then, I spent years running external balanced iron block race motors, trapping them at 6500 or higher. I never had a failure that could be traced to balance or harmonics, and never had issues with number 4 main.

    So better.. sure.. required?... matter of opinion, and that is not to say your opinion is wrong, it's just different than mine..

    The other reason I don't suggest the internal balance conversion on the internet, is that there are too many hacks out there in machine shops, and the conversion process is a place were the hack really comes out in some of these guys.. The disaster stories I could recount from the conversion done wrong, and bending the crankshaft, to the heavy metal coming loose in the crank, and exiting the assembly, while creating massive damage.. or just the complete mess I have seen from an unskilled welder.. all lead me to not recommend the conversion.

    My blanket statement on the issue is this... Street/Strip motor- a well executed external balance job works just fine. Going Racing?.. looking for 650+HP?.. Invest in a Billet crank.. it resists flex in the engine, making the whole assembly more rigid and reliable, has the center counterweights for easy internal balance, and the engine at 523ci is going to make a whole bunch more power than anything you can reliably do with a stock crank.

    And if the budget allows, put that nice new crank in a new HD block, the current aluminum one from TA, or the iron one that hopefully is coming soon from Ken Betts.

    The availability of a $2800 drop in Billet crank is a game changer here for that 650HP plus race engine. Compression and cubes make power, simple as that. Until recently, by the time you got it rough balanced, a Billet from crower would set you back about $4200 bucks.

    The new crank nearly halves that cost, and changes the need/benefit/cost equation.

    Ken Betts was the force behind getting this new crank made, you can check with him on prices and availability, but I suspect that I will have them on the shelf for builds in the future. I worked closely with Tom in the design phase, and am proud of how it turned out.

    If the budget is a crunch.. then get the crank, and put your alum heads on hold for a while.. heads are bolt on stuff, not so much for the crank.

    JW
     
  12. Thumper (aka greatscat)

    Thumper (aka greatscat) Well-Known Member

    I don't disagree with your take on things Jim, its just we approach where certain things are done on a different hp levels or stroke. I know my original Thumper motors I built in the 80's were ex.balance and no girdles, not a very available item back then, but al. rods and Venolia pistons to keep the reciprocating weight down. Every winter I just knew #2 and #4 main bearings needed to be replaced due to block flex and maybe balancing,not sure. But normal maintenance. HP level was around 625 with the iron stage2's and 10.40s, not bad for 1984.
     
  13. Jim Weise

    Jim Weise EFI/DIS 482

    Ya Gary, Alum rods and light pistons go a long way in keeping the block stress down. While I try to talk every customer building a new race motor into them, the old stigma about alum rod life lives on.

    I tend to agree with what Scotty told me a long time ago " Steel rods in a race motor?.. I don't want all that weight swinging around in there".

    Of course, if know Scotty, you know I left out a few words to make that quote "family friendly" :eek:

    JW
     

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