Crankshaft Cross Drill Oil Channel

[Porshaah]

Hi All

Will a center drilled main crankshaft still benefit from extra lubrication or at least have no detrimental effects if no groove is cut in either the crankshaft journal or bearing halves?

All responses appreciated

[TT Oversteer]

When I built my 3.2 I had my center main journal crossdrilled. I did not groove the crank journal or the bearing. I talked to two different expert builders and got two different opinions. One said it would help provide lubrication to the two adjacent rod bearings which are usually the last to receive oil pressure that normally comes from either end of the crankshaft. The other builder said crossdrilling is a waste of time unless you also groove the journal or bearing and open up the diameter of the oil supply passage in the engine case itself to the center main bearing. And you should also use a turbo oil pump if you want to really do it right. So the question is: do you really need it? What are you using the engine for? How fast are you going to spin it?

[turbobrat930]

Contact Mr. Mike Bruns at JB Racing in Florida....

[Porshaah]

Originally Posted by TT Oversteer

When I built my 3.2 I had my center main journal crossdrilled.

How long has it been running like this?

Originally Posted by TT Oversteer

So the question is: do you really need it?

Not really. If I had my choice I would have preferred it wasn't cross drilled but it was local and all other aspects of the crank were good including the price.

Originally Posted by TT Oversteer

What are you using the engine for?

Non track use

Originally Posted by TT Oversteer

How fast are you going to spin it?

Factory red line once in awhile.

Thanks for all your responses

[KTL]

Cross drilling is overkill for a non-tracked engine, especially if you're spinning it below 7000 rpm. There are tons of people who track/race their engines and the lack of cross-drilling isn't blowing these engines up regularly. It's only for the high revving engines for added insurance in getting the oil to the #2 and #5 rod bearings more effectively.

The theory/reasoning behind the cross-drill is because it is a known fact the crankshaft is fed oil from the ends. Main bearings #8 and #1 feed oil into the crankshaft and that's the source of oil for the rod journals. Since #2 and #5 rod journals are the centrally located rods, they get oil last. If oil demand/loss is high on the outer journals, then the inner journals like #2, #5 are going to suffer.

Also noteworthy is the #1 main journal is grooved, which helps the oil find its way into the drilling in the journal. #8 is not drilled I assume because the bearing insert is much wider and has a better ability to feed oil into the crank at that end? Not sure there.

The #4 bearing hole, and of equal importance is the hole in the case saddle leading all the way to the oil gallery inside the case, is enlarged to ensure the cross drill effect is taken advantage of. The larger hole is the path of lesser resistance and that means the oil path is going to be activated more easily than the surrounding paths that have smaller holes leading from the case main gallery to the main bearing saddles.

Here's a good thread with some pictures to describe what's going on with the oil path

Another crank cross drill question

[TT Oversteer]

It sounds like you may have gotten this crankshaft already drilled and are wondering if there are detrimental effects to drilling? Based on your original post I would say there are no detrimental effects to cross drilling without grooving but there should be some benefit to lubrication of the two rods closest to the center main journal. I wouldn't worry about grooving it if you are just going to build a stock motor. I would say all upside in your case and no downside if you didn't pay extra for a mod you didn't really need. I have only a couple of thousand miles on my build but all seems fine with it. I guess I won't really know whether crossdrilling was good bad or indifferent unless I blow up the engine then tear it down and see.....

[Henry Schmidt]

We cross drill every crank on every motor we build. Overkill ? maybe, but the process is cheap insurance. One of the cool things about building an engine that has 50 years of development is you get to incorporate everything you learn along the way.

We can groove your bearing with a one day turnaround.

[GaryR]

Send the bearing to Henry for grooving, then forget it's all done. Why wouldn't you, regardless of it's intended use, since the hard part (crank) is already done! CHEAP insurance!

[CaptainCalf]

Originally Posted by turbobrat930

Contact Mr. Mike Bruns at JB Racing in Florida....

+1