Basic Oiling Question
 

I have read a lot of stuff on this board about improving the oiling system of the flat six. But I still have some qestions.

http://forums.pelicanparts.com/uploa...1278644644.jpg

This is a crankshaft for the 4 cylinder 2.0 the rods are oiled from the mains with 0.214" diameter holes.


http://forums.pelicanparts.com/uploa...1278644738.jpg


This is a 70.4 stroke crank from the flat six. It oils from the front and rear mains only and has 0.125-0.135" diameter holes. It seems to me the four cylinder crank is far superior in moving oil to the bearings. Why not drill all the main journals to pass oil to the rods on the flat six?

Thanks,

neilca

Common mod

Pelican Parts Technical BBS - Search Results

I understand the center main drilling is a common mod. I am thinking of drilling all the mains and grooving all the main bearings.

I did more searching and found this thread. Seems Henry is ahead of the curve as usual. The answer is yes you can cross drill all the mains for better oiling.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/230656-cross-drilling-crank.html

I was rereading the cross drilling post and thought of another question. How large can you increase the oiling holes in the crank without sacrificing strength?

The hole in the crank only needs to match the leak rate of the rod/journal. Larger won't benefit uness your running large clearances.

It seems the bottom line is to overcome the centripetal forces added to the oil inside the crank as it spins. Cross drilling does that as does the pressure trickery the 993 does (from what I understand it's no cross drilled).