I have always read not to use a cross drilled crank, but now I have been supplied with a Eagle crank to build a motor and it is cross drilled, as this is my first one I've seen. At what power level is it a problem?

 

Steve,

DR guys like Big Daddy Dwane Guthridge are in the 7's at 170+ on these cranks. Cross drilling is actually not a bad thing, it helps supply the mains with oil at low and high RPM. The purpose of cross drilling the main bearing is so that the oil hole feeding the big-end journal can be supplied with oil on a more or less continous basis.

Bret

 

well I was just going off Reher Morrison site, and this article

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

 

Hard to argue with RMRE. Then again how much RPM is this new motor going to see?

Bret

 

I think a lot of Dave Reher's comments, and his discussion of rod oiling and cross drilling makes sense, especially if the rod oil holes intersect at the main journal centerline. You might check to see where they intersect on your Eagle crank, and compare them to a stock crank. Perhaps the "race oiling" drilling was the big difference when he had with his oiling problem.

Not to second guess DR, but maybe the thought on cross drilling, (even with "race oiling" offset drilling to the rod journals) is to get two shots of oil per rev into the journal. The "race oiling" drilling is a better fix, but combined with cross drilling is it as good or better? It could be expensive to run the tests to find out. I'd base my oil pressure on what kind of rod drilling your crank has and how high you are turning it. The problem increases at the square of the rpm.

One reason Pontiac V8s, especially the 421-428-455s with the 3.25(!) inch mains had trouble revving high was the very thing Dave referenced: the inertial (centrifugal) force from the long (1.625) column of oil from the surface to the center of the main. Of course Smokey just cut down the main journals when he needed to rev the NASCAR 421s. I don't think he told anyone for many years. That helped lower bearing speed also. As I recall, Pontiac was very concerned about journal overlap being big enough to guarantee virtually indestructible production (cast) cranks. The large overlap was probably way overkill for the forged crank Super Duty engines, but they never changed the main jounal size on the big engines. I don't recall if they ever went to the offset "race drilling" for rod oiling. Probably not.