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35WINDOW 02-14-2006 12:58 PM

Cross Drilled Crank
 
Hey guys,

I ordered a new 4340 Crank and H Beam Rods (w/L19 bolt upgrade) for my 454 (Gen VI) to make it a 496. Anyway, I am gettng a Cross Drilled Crank. I have heard in racing applications Pro's and con's to running one:

Pro-better Lubrication

Con-weaker-maybe-

This is for street use, and I probably don't need this, it may be overkill, but I am looking for a turly dependable, take some abuse Engine-

What is everyone's take on a Cross Dilled Crank?

Alexandre Garcia 02-14-2006 01:05 PM

35window,

The pro of better lubrication can be achieved with full groove main bearings, so if the weakening of the crank disturbs your peace of mind, the advantage can be had in another way. But I do not think it weakens too much to the point of compromising the engine reliability in street use. It is said also that it makes more oil splash around the crank and so more oil to the cilinder walls loading the oil rings a little more, then maybe some more oil consuption. I'd not avoid using a full groove main bearings just for that. Using a better oil pump would be wise.

onovakind67 02-14-2006 01:29 PM

Reher-Morrison has a treatise on cross-drilled cranks:

I’ll begin with a rather bold statement: Don’t use a cross-drilled crankshaft. There are a few exceptions to this rule, but under most circumstances, a cross-drilled crank is going to cause big problems.

Unfortunately cross-drilling is one of those terms that’s become part of the jargon of hot rodding. People who know very little about racing engines have heard of a “cross-drilled crank,” and mistakenly believe they’ve got to have one. In fact, cross-drilling simply refers to the position and routing of the holes that carry pressurized oil from the main bearing journals to the connecting rod bearings.

In a cross-drilled crankshaft, oil feed holes are drilled completely through the main journals so the passages are open on both ends. Holes from the rod journals are then drilled at an angle to intersect the holes in the main jouranls at the centerline of the crank. This system was thought to ensure a continuous supply of oil to the rod bearings because one end of the passage drilled through the main bearing is always exposed to the pressurized oil in the upper main bearing insert.

So what’s wrong with this picture? The pressurized oil that enters the feed hole through the main bearing journal must overcome the centrifugal force created by the rapidly spinning crankshaft before it can reach the passage to the rod journal. If the pressure created by the oil pump is not strong enough to counteract the centrifugal force that is pulling the oil away from the rod journal feed hole, then the rod bearing is starved for lubrication. Since the pinwheel effect of the centrifugal force increases with rpm, when the rod bearing does run dry and seize, the resulting carnage is usually catastrophic.

I learned my lesson about cross-drilled crankshafts the hard way. Back in the early ’80s we started to turn our engines faster. We’d been running stock Chevy cranks in our 287-cubic-inch small-blocks and B/ED motors without any problems. Eventually the supply of usable cranks became exhausted, so we ordered aftermarket cranks – “California cranks” as my Texan friends called them. These cranks were much prettier than the factory forgings, and they all had trick cross-drilled main bearings. It didn’t take long for those cranks to turn blue when the rod bearings burned, sometimes on the first or second dyno pull. Then we’d bolt in an old 283 crank and the engine would live forever. So what was the difference? The difference was the cross-drilling.

Today most racing crankshafts have a “high-speed” oiling system, which is essentially just how Chevy drilled those stock cranks. The oil feed holes for the rod bearings intersect the main journals at or near the surface of the journals. The pressurized oil does not have to overcome centrifugal force to reach the oil feed holes for the rod bearings, so the supply of lubrication is constant even at high rpm. There have been some refinements made to the angles and positions of the oiling holes to “time” the oil supply, but the basic design hasn’t changed significantly.

It’s easy to spot a cross-drilled crankshaft. Insert a piece of welding rod or coat hanger wire into the oil hole drilled in the main bearing. If the wire comes out the other side, the crank is cross-drilled. My advice is not to use it.


http://www.rehermorrison.com/techTalk/51.htm

35WINDOW 02-14-2006 02:21 PM

onovakind67,

Your Post couldn't have been more timely-I was able to call them and change my order, but you are correct-they are only stocking Cross Drilled Cranks and will have to order a "Standard" unit for me-

Thanks again, I know I will sleep better now-

Craig


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