BBC Steel crank cast#7115 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-19-2008, 04:46 PM
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BBC Steel crank cast#7115

Have a couple questions...if you smarter than an old guy like me.
Just this second ago (1/2 hour) I bought a Z-16, L-88/ZL-1
5140 std/std crank. Did the tuning ring test on her and it is stamped
"7115". Apparently this is cross-drilled, tuffrided with 7/16" bolts.
Plus this thing has the chamfered oil journels and chamfered mains, rods.
Suppose to use Clevitt chamfered bearings.
Does the 7/16" mean that the main caps have 7/16" bolts? Anything more you
could tell me would be great. This is for my 396 cast #3855962 block
4-bolt. She is a rare one. I was planning on boring out to 4.25" and making
me a 427 with the L-88 solid cam for my 65 Malibu.
Things to look out for in my build etc.. would be great. Plus this crank has been magged. I spent $500 cash. Think I got a great deal since they go for
more twice that much when you can find them. The is one on Ebay right now for $1800.
Anyway your knowledge/experience would be great.
Thanks
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Old 09-19-2008, 10:09 PM
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7/16" is referring to the rod bolt size....
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Old 09-20-2008, 02:30 AM
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Never have cross drilled a crank, so have no personal experience, but pulled this from another of my posts about the subject. I present it herewith for your perusal.....

"David Reher of Reher/Morrison recently reported having experienced rod bearing failures in big block Chevrolet engines with cross drilled crankshafts; replacing those crankshafts with cranks not cross drilled seemed to cure the problem. Here’s the theory: a ½ groove bearing only supplies oil to the rod journal for 180 degrees of rotation, the other 180 degrees residual oil lubricates the rod journal. Cross drilling provides another source for that oil because as one oil hole passes the end of the oil supply groove, the other hole opens up to the groove. But, here’s the problem; in a cross drilled crankshaft, oil has to fight centrifugal force trying to flow to the center of the journal before flowing to the other side where it can feed the rod bearing. If pressure is inadequate to counteract the centrifugal force, oil will actually be forced out of the cross drilled passage and can potentially obstruct oil flow! Oldsmobile big blocks typically have what is referred to as a "fully grooved" main bearing. The oil supply groove runs the full circumference of the bearing. There is really no need to cross drill the crankshaft as the rod bearings have continuous oil flow. Remember, the oil feeding the rod journals from the main bearings do not go through the center of the main journal, these passages are angled toward the rod journal so oil passing through these passages face only a fraction of the centrifugal force that the oil passing through a cross drilled passage would face. Bottom line: in my opinion, don’t cross drill your crankshaft!"
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Old 09-22-2008, 02:23 PM
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#7115 Forged BBC crank & 7/16" rod bolt question.

I have this forged steel 7115 Z-16, L-88 crank and the
specs for it say 7/16" rod bolts. Does this mean I have to purchase a new set of 7/16" rods/ARP bolts or the 7/16" bolts just add strength and I could still
use regular BBC rods 3/8" bolts or thumb rod with 3/8" bolts? I mean the crank end of the rod is the same size and width for my crank right???
Help??
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Old 09-22-2008, 07:34 PM
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The rod journal size is the same, the counterweight structure is probably made and balanced for using the (heavier and beefier)7/16" rods and (heavier)high compression pistons! Meaning, at the least you need to at least check the balance with the new components you will be using, since they will most likely be much lighter! 3/8" rods will be fine.....
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