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Old 02-08-2011, 06:49 PM
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Cross Drilled Crankshafts

I've been hearing ups and downs about these, and that they break a lot.. What's your opinion? I've found a 3856223 that's a steel non-X Drilled Crank for 170.. What are your thoughts? This is what they came out of:

3856223 396 65-69
3856223 402 70-71

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Old 02-08-2011, 07:04 PM
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Cross drilling is old skool. The major aftermkt crank suppliers don't do it. I have not seen a BBC crossdrilled crank break. Not saying they don't. But there would have to be a major problem to cause breakage..
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Old 02-08-2011, 07:08 PM
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As if my crank is NOT crossdrilled, it's oiling from the inside out.. Is that correct? What's the advantages/disadvantages of that?
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Old 02-08-2011, 07:09 PM
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Quote:
Originally Posted by Wattsy
I've been hearing ups and downs about these, and that they break a lot.. What's your opinion? I've found a 3856223 that's a steel non-X Drilled Crank for 170.. What are your thoughts? This is what they came out of:

3856223 396 65-69
3856223 402 70-71
No they don't break a lot. On the other hand the grooved cranks would, but you had to put a lot of power on them to do it.

Unless you're running over 6000 RPM as steady diet, there really isn't any need to cross drill the crank. Even then up to that point or maybe to 6500 3/4 groove bearings might be the choice to put a little more oil on the rods. Getting beyond that point I like going with a 1/2 groove bearing and cross drilling. Cross drilling and high RPMs take doing other tricks because the centrifugal forces in the crank's oil passages can out flow the pump's ability to feed the mains. You can go with a higher volume pump and deal with the oil control issues or jet down the delivery hole, after-all you're now feeding the rod journal all the time so a little less oil at any moment stretched over more moments works to solve the original problem of keeping more oil on the rod when it's loaded the most. Reducing the outlet by 25 to 30 percent is fine, this helps reduce the power used to run oil pumps and having to deal with so much of a flood in the crankcase.

Bogie
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Old 02-08-2011, 08:21 PM
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Gotta admit that cross drill is old school but I never had any problem with them due to the cross drilling.

The crank co's have many engineers well schooled in hydrodynamic lubrication so you are very unlikely to improve on it at home or even in the shop. Polish it and run it.
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Old 02-08-2011, 08:41 PM
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Please correct me if I'm wrong, but didn''t cross drilled cranks come about before the advent of grooved main bearings?
Vince
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Old 02-08-2011, 10:43 PM
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I don't really remember exactly. I know our old welded strokers for the 392 were cross drilled. We also tried the full groove main bearings. They didn't hold up well at all and most all of us went to grooved top half. I think the aftermarket SBC forged cranks were cross drilled in the 60'. I just don't recall.

I don't recall any actual grooved cranks. What were they in???

I think the early race 426 tried full groove bearings too but are now using top half only. I'll check at the shop tomorrow just to be sure. Not my game anymore. We just got a new 3/4 in arm 426 crank a couple days ago so I'll check out the oiling. I'll try and get some pictures.
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Old 02-09-2011, 07:47 AM
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Here's David Reher's opinion of Cross-Drilled Cranks-


http://www.rehermorrison.com/blog/?p=214
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Old 02-09-2011, 09:43 AM
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Crossdrilling cranks

Cross drilling the crankshaft main journals is a common high performance up grade when using half - groove main bearings. Half groove main bearings provide a wide bearing surface on the bottom of the main journal for better support but they only provide oiling to the rods through 180 degrees fo crank rotation.

Main bearings are half-groove beccause the bottom side of the main bearing receives the highest load. Cross - drilling the main journals of the crankshaft is a high performance modification in order to provide 360 degrees of oiling to the rod bearings. The extra oil passage through the center of the main journal prevents the rod bearing oil feed hole from being cut off during 180 degrees of crank rotation. When using half-groove main bearins in lieu of cross drilling the crankshaft provides two narrow bearing surfaces and is asking for main bearing failure in a high performance application.

I have never used half grooved main bearings wheather the crank was crossdrilled or not. In fact, I did not even know they made full groove main bearings for BB Chevy and 455 Pontiac engines. The 455 Pontiac cranks I have used were "double" cross-drilled and required the use of a 80 lb. high-volume oil pump to maintain a maximum of 60 lb. oil pressure. Crankshafts will not break due to being crossdrilled.

The only crank I have ever broke was a 327 CI Chevy cast nodular iron crank in my '56 Chevy M/P race car and that was due to crank fatigue because the engine was out of balance. Cranks will always break at the rear main journal, turning a V8 crank into a V6 and a V2 crankshaft.

Last edited by MouseFink; 02-09-2011 at 09:54 AM. Reason: typo
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