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SBC crankshaft hub w/6:71

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George:
I am putting a 4.125 X 3.48 SBC together. We have a RCD girdle but I'm concerned about the wall thickness of the available hub. I have a 3/16 and 1/4 keyway on the crank. Should I look for a BBC OD hub? The timing chain cover is a cast Hilborn so cutting it for a larger seal is no biggie. I am also wanting to run my MSD crank trigger . I spoke with Randy @Good Vibrations today and left a VM with John Lane at ATI. Thanks. George

OH, also got a question on "burndown breathers" . Are they all for 1.25 hose? I'm looking at the cast units with the quick connects. Pretty pricey! Any other options or parts available.

dreracecar:
By all means go with the BBC OD hub, There is not enough material between the .250 keyway and the SBC hub OD and you will split the hub and rotate the key out the crank snout even with the support. If you already have the SBC hub then you can shrink a piece of moly material and machine down to BBC OD that way if the hub does crack it will hold because the crack stops at the ID of the over tube. How do I know this--myself and 4 others racers I know of have all gone thru it.

As far as a crank trigger, is that for standard ign or a magneto?

George:
The only hub I have has no snout. The crank trigger is for the MSD 12lt mag.

dreracecar:

--- Quote from: George on March 11, 2014, 07:29:16 PM ---The only hub I have has no snout. The crank trigger is for the MSD 12lt mag.

--- End quote ---

Missing somthing here--- "snout" is the end of the crank, "hubs" have pulley registers, "girdles" support the crank and pulley under load while using a blower on a SBC because the crank snout does not stick out far enough and puts a load on the hub,streching the 7/16 crank bolt, losening up the hub,causing the hub to flex and crack along the 1/4" keyway,rolling the key out of the crank and really messing up the crank seal, pukeing out oil all over the front of the engine and on the track.

By going with the ATI hub or shrinking material over a standard SBC blower hub, you eliminate the hub itself flexing and will not crack along the keyway. But even with the girdle I have seen the standard blower hubs split apart and do the same amount of damage.

George:
So there is no one making a crank hub with a SBC I.D. and a BBC O.D. long enough to be carried in a outboard bearing?

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