[69Goat1]

I was talking with the Machine shop about High RPM's and Pontiac Cranks - He has been studying and talking with Callies and Oliver on their cranks and noticed none of the high end cranks are cross-drilled like our old Pontiac Cranks - Apparently at around 6000 RPM crossdrilled cranks start throwing the oil out instead of letting it get to the rod bearings like it should. Has anyone here ever heard of having a cross-drilled crank plugged on each main going from one side to the other all the way back to save bearings? One side remains open for lubrication but the other is blocked to let oil get to the rod bearings.

Just something I thought was interesting and wanted to know what you guys thought...

[screamingchief]

David Reher does'nt recommend cross drilled cranks:

From the R-M website:Crank calls pt.2,"tech talk" article #51,by David Reher;

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.

It is possible to crank up the oil pressure high enough to overcome the negative effects of cross-drilling. However, excessive oil pressure creates its own set of problems, increasing parasitic losses due to windage, excessive oil on the cylinder walls, and the power that’s consumed by turning a high-pressure oil pump

FFT.
Bret.

[Jack Gifford]

First an attempt at a direct answer for your case- with the availability of 3/4 groove main bearings, most Pontiacs are better off without the cross-drillings- assuming no aluminum rods and engine speeds in the range of 7,000 RPM and below.

The more-generalized answer is more complex, and must take into account many other engine details. For example, my blown-alky Pontiacs needed the mains cross-drilled as part of the overall scheme, to let them live at up to 9.000 RPM for many seasons. The David Reher quote makes some important points, but is somewhat flawed. The most glaring flaw is to compare his experience with a 'high-speed-drilled' crank versus a cross-drilled (non 'high-speed-drilled') crank. And for whatever it's worth, I doubt that many of us could consider the 'high-speed-drilling' of a Pontiac crank.

[Half-Inch Stud]

Chevy is a different world of hurt.

[screamingchief]

Well the new BOP/All Pontiac forged cranks reportedly are gonna do away with crossdrilling as SOP,so apparently they agree with David Reher too.

Read me,crank thread.

And most of the "high end" billets have gotten away from crossdrilling too,so there's gotta be some merit to the theory to lead to such changes.

[Half-Inch Stud]

Do these new-age non-cross-drilled cranks have a Main Bearing Recommendation to be successful? such as Bearing Groove Duration & Distance from the Top-feed hole?