Turned BBC cranks, teach me. :)
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From: Boston, MA
Turned BBC cranks, teach me. :)
We're picking up a 454 Mark IV 4-bolt block for my father's 67 vert project on Saturday that we found from the tip of a friend. Anyways... the stats on it as of right now are that the bore is 4.290" and the forged crank is turned 0.030" on the rod journals and 0.020" on the main journals.
I honestly don't know what my dad plans on making for power, but if I were to guess I'd put it in the 475-525hp range. Anyways, what are your thoughts on using that crank? Good? Bad? Indifferent? From talking to dad he seems to think it will be fine as long as he doesn't try to turn it into a top fuel car. :)
Are there any unwritten rules or guidelines as to how far you should take these cranks before special considerations need to be made?
Thanks. :seeya
I honestly don't know what my dad plans on making for power, but if I were to guess I'd put it in the 475-525hp range. Anyways, what are your thoughts on using that crank? Good? Bad? Indifferent? From talking to dad he seems to think it will be fine as long as he doesn't try to turn it into a top fuel car. :)
Are there any unwritten rules or guidelines as to how far you should take these cranks before special considerations need to be made?
Thanks. :seeya
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Re: Turned BBC cranks, teach me. :) (scorp508)
with any used crank get it magnafluxed. is it forged or cast crank? if the proper radius were ground in the corners and it passed mag it should be fine. :chevy
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Re: Turned BBC cranks, teach me. :) (scorp508)
Sorry, I might be using the wrong terms for the areas that I'm referring to.
By "turned" do you mean that they reduced the journal's diameter??
Wouldn't this mean that you have to use shimmed bearings or something??
Wouldn't the crank journals have to be heat treated after the turning to re-harden the surfaces?
Is there any way to verify that the crank was indeed re-heat treated after the machining?
Just my $.02
By "turned" do you mean that they reduced the journal's diameter??
Wouldn't this mean that you have to use shimmed bearings or something??
Wouldn't the crank journals have to be heat treated after the turning to re-harden the surfaces?
Is there any way to verify that the crank was indeed re-heat treated after the machining?
Just my $.02
Drifting
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Re: Turned BBC cranks, teach me. :) (scorp508)
Check out WHY it was turned. I had one motor that badly spun the bearings. The crank was turned .010 under and mag checked. It looked beautiful after the work, nice polish, radiused oil holes and journals, the works.
It still broke in 2 after only 10 hours of running (although I will admit 10 hours in my boat is much harder than your car). 0.030 under is a LOT in my book for a BB crank (and is much deeper than the factory nitriding would have gone.
If it was me I'd juet get a new crank, much cheaper than building the motor a second time. Last GM crank I bought it took checking 6 before we found one that was usable. They were really getting to the bottom of the supply for Mark IV cranks. I'd just buy a good new forged aftermarket one.
$0.02
-Greg
It still broke in 2 after only 10 hours of running (although I will admit 10 hours in my boat is much harder than your car). 0.030 under is a LOT in my book for a BB crank (and is much deeper than the factory nitriding would have gone.
If it was me I'd juet get a new crank, much cheaper than building the motor a second time. Last GM crank I bought it took checking 6 before we found one that was usable. They were really getting to the bottom of the supply for Mark IV cranks. I'd just buy a good new forged aftermarket one.
$0.02
-Greg
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Re: (scorp508)
sorry about that i guess i did not read close enought,but if it passes magnaflux it will work. if it shows cracks toss it. a quick check for a cracked crank is to hit it with a hammer and if it does not have a crack you shoild give of a sharp "ring". i have found this works when checking used cranks before sending of for magnaflux. i have ground brand new cranks to 10-10 to get the indexing corrected because production cranks can be off. these cranks were used in engines that produced 800 HP supercharged and run in 110 MPH boats.:chevy
[Modified by clem zahrobsky, 12:33 PM 3/28/2003]
[Modified by clem zahrobsky, 12:33 PM 3/28/2003]
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Re: Turned BBC cranks, teach me. :) (scorp508)
I agree with your Dad. Of course, as advised above, have it chaecked out. You would do that with any crank you were reinstalling upon rebuild, previously reground, or not. I don't believe that Chevrolet ever produced any cast, MarkIV cranks. Good luck, and...
RACE ON!!!
RACE ON!!!
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Re: Turned BBC cranks, teach me. :) (clem zahrobsky)
all 454 PU trucks and pass cars were cast cranks :chevy
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Re: Turned BBC cranks, teach me. :) (scorp508)
My rule of thumb on the purchase and reuse of a sat NDT'd crank, cast or forged is:
How much are you saving?( Oversizes rod & main bearings cost & clearance issue?)
Machining concentricity and TC better be right on.
Was it balanced?
Why was in turned?(I would not by a shock loaded crank, .030 is a lot!)
.010-.020 is the norm for turning
How much is a similar crank new and if you use this one....if it breaks how much $$$ will you destroy?
:cheers:
How much are you saving?( Oversizes rod & main bearings cost & clearance issue?)
Machining concentricity and TC better be right on.
Was it balanced?
Why was in turned?(I would not by a shock loaded crank, .030 is a lot!)
.010-.020 is the norm for turning
How much is a similar crank new and if you use this one....if it breaks how much $$$ will you destroy?
:cheers:
