crossdrilling crank
Turbo Mini Forums

is it worth doing on a 1380 with 12psi?
or is it better for high rev engines?

Definately a high-revving engine thing...

If your wallet says yes, and you feel it's needed - then do it. Way i see it though, drilling a hole through a crank is adding a failure point. So if it's not needed - then don't add it.

that's what i was thinking thanks

My first Swiftune crank was just wedged, it was fine for upto 9000rpm, it lasted over 2 years before I spun centre main.
Paul

I seriously doubt it!

is it any point in crossdrilling both the mains and big ends? or are just the mains necessary?

The thing is, that all cranks have the hole in the big end on the wrong side. It should be on the inside, towards the main centerline, not the outside. However, this contributes to large costs.

Crossdrilling mains is better as you are sure that big ends are lubricated always.
This is a good thing when using stupid A+ bearings, but it seems as the factory setup works fine.

I know it says somewhere, but NO A+ cranks have got cross drilled mains.

If you look at an A+ crank closely, you will see that the oil holes in the main journals are not at the same angle. so oil is fed from more than one bearing at different degree angle of rotation. There is always oil fed to the bearings, despite what ive read else where, saying that because of the plain bottom bearing there is no oil feed to the big ends through half the rotation.

Cross drilling has to do with reducing the length of the path the oil has to take to get to all the bearings, reducing the centrafugal forces at high rpm. I suppose you could crank up the oil pressure to counter act this.

Im sure i read some where tha it was 10psi oil pressure for every 1000 rpm

Edited by Sprocket on 24th Oct, 2006.

What do you mean by not the same angle? There is only one hole in the journal. That's the problem.

I agree. Cross drilling is to avoid sentrifugal effect on the oil to the big ends. That's why on decent crankshafts the hole fromt he main journals are only drilled to the middle of the big end. and then a new hole is drilled from the "inside" of the BE journal to the gallery which ends in the middle of the BE. This reduces the centrifugal effect, and dioes not weaken the crank by drilling hundreds of holes through it.

Sorry, old thread revival

I have been thinking about this today, I'm probably going to build a pretty revvy 1380 in the near future and was wondering whether there would be much point in crossdrilling the big end bearings. The way I see it drilling numerous holes through the journals only serves to weaken the crank.

I'm think I might only cross drill (really just through drill I suppose) the mains, just to ensure a consistant oil supply to the big ends.

The engine will be limited to about 7500 rpm, though will be used for track days so sitting at fairly consistantly high rpm.

What are peoples experiances with cross drilling 2 years after this thread started then?

James