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Old 03-05-2012, 11:11 PM
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big block chev hp rotating assy clearances

I'm building a 400 pontiac motor with a scat crank which suit 6.800" big block chev rods . Could anybody help me with clearances on the big ends and the rod to crank side clearance .

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Old 03-06-2012, 05:40 AM
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I'd call/e mail scat..
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Old 03-06-2012, 10:06 AM
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As far as rod bearing oil clearance, not much different than the Pontiac rods. Depending on use, I like to see .0015" min to about .003" for serious max but sometimes there's not lots you can do, reasonably. I've put them together with as little as .001" on fresh machinework(round) and as much as .004" when used eggshaped rods were used and they all worked. For rod side clearance, I like to see .010 min to .020". Once again, you can carefully make it larger if it's too tight but you can't make it smaller. I've seen them run fine with .040" or more. By the way, the old tale about using oil if the side clearance is big is just wrong. Don't worry about that.
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Old 03-07-2012, 03:56 AM
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you've reused eggshaped pontiac CAST rods. as is.?
really..
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Old 03-07-2012, 04:48 AM
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Big block rod clearance .

Thanks for your help guys , much apreciated
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Old 03-07-2012, 07:34 AM
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Quote:
Originally Posted by speedbump
...(Side clearance) I've seen them run fine with .040" or more. By the way, the old tale about using oil if the side clearance is big is just wrong. Don't worry about that.
I believe you're talking about a drop in oil pressure, not using oil, and is it something to be concerned about if you're building it right, but then if you reuse oval rods, why worry about it.
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Old 03-07-2012, 08:17 AM
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I didn't say it was correct, but it worked OK. Sometimes customers, budgets and just plain lack of knowledge can have you do things that aren't pristine. The point is they can work if they have to. Unless you have used new or Sunnen reconditioned rods in every build you do, you have used egg shaped rods. Might only be .001", but they aren't round. I spent a lot of money on a precision gauge for my Sunnen hone just to measure connecting rods. I was amazed at how used rods stretch, but then I didn't already know everything. I'll leave it to you to explain how, with .0015" to .0025" oil clearance which controls oil pressure, rod side clearance, no matter how much, is going to affect oil pressure....unless it's smaller than .0015".
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