cross drilling 5 bolt main for rpm

[Mochi]

I have been reading posts on cross drilling the 3 and 5 bolt main crankshafts for better oiling.
https://www.datsun.org/fairlady/JoeEngine.htm
http://datsun.org/roadster/resources/sharp1600.pdf
viewtopic.php?p=282141&hilit=Cross+drilling#p282141
My speed shop that is doing all the balancing and block prep said that is not what you should do as it would starve the the bearing at high RPM.
Is this a bad idea? it seams like racers have done this with success. I want to do this but would like a little more affirmation before i commit to machining my crank. My machinist is lightening my another flywheel right know and said is willing to do the drilling.

[redroadster]

My 2 cents I wouldn't do any mod
1 it has plenty of oil flow stock with a perfect pump
2 it might cause a rope rear main seal leak easier
3 the bit could break off & jam in the drill hole
Are you unfamiliar with the problems of over reving ,big valves pushrod & non balance shaft engines , especially on road courses?

[keith0alan]

My experience is that if you are going over 7,000 rpm then you need to do the cross drilling. It is a very tense job. You need to use a carbide end mill to create a flat and then a carbide drill to make the hole. Yes, you certainly can scrap a crank with a wrong move. I can see why a shop would be reluctant to do it. If you want one done I would recommend going in with two good cranks. On the 1600 race engine we used a 2000 oil pump with the oil pressure relief shimmed to increase pressure so oil pressure nor flow was not the problem.

[JT68]

Crossdrilling is smart on the 1600 cranks for racing. If you don't cross drill, the 1 and 4 rods get twice the oil flow of the 2&3. That is why 1600 almost always throw a #2 or 3 rod.

For street, it isn't necessary (unless you drive it crazy hard), just use the 2L pump and it will probably survive ok.

The H20 crank is the worst setup for high rpm since it shares the same oiling issue-The additional acceleration load due to the increased stroke makes them more fragile than the 1.6. The longer the stroke, the more likely the failure.

U20 cranks do not have this problem.

[Mochi]

Thank you! That is what I needed to hear. I have a u20 pump already. I do not want to go into every autocross/trackday and have the feeling like I am destroying my engine. Sorry for the stupid question why would the u20 crank not having issues? I thought in some race prep guides they still did some kind of mods to the u20 crankshaft.

[david premo]

U20 cranks are factory cross drilled.

[Mochi]

My 2 cents I wouldn't do any mod
1 it has plenty of oil flow stock with a perfect pump
2 it might cause a rope rear main seal leak easier
3 the bit could break off & jam in the drill hole
Are you unfamiliar with the problems of over reving ,big valves pushrod & non balance shaft engines , especially on road courses?

I must heed your warnings! i am unfamiliar with what you are talking about on road courses. if you dont mind directing to a book or telling me why? I understand weight and stroke when it comes to high rpm. Maybe i will build my numbers matching engine(3 bolt) to be high revving.

[Daryl Smith]

Irrelephant

[redroadster]

The oil pump would pump what. 6-8qts out in 30 45 sec. @3k Thru the oil sender hole , ya ever done that ? and 3/4 th of that goes to the crank but a fraction of that can escape the thousands clearance of the rods and mains
And on a 1600 rope seal Changing volume
Oh you mean the last , push rod engines can't really compete with a overhead cam in high revs , near recline " long term " the lifter and push rod add weight to the moving parts of what opens and let's close valves at 50 X a second.
I was a weekly grudge night spectator and occasional racer in 70s &80s more gymkana then
Mitsubishi 4g63 has 2 balance shafts 1 main and a high speed just saying reving it 7500 no much to worry about

[Daryl Smith]

Irrelephant

[Mochi]

i do want to add that i do have a harmonic balancer from dean, spent way to much money on light rods and pistons haha(mondello rods and vg30 pistons). the whole rotating assembly is being balanced right now. i have not finalized what i am doing with the head but will be building for light high rpm use. even the cam is aggressive and my grinder says will sing when in the higher rpm range. i dont want to assemble the short block and regret not doing something that will hinder me letting the engine rip!

[david premo]

You should have the crankshaft cross drilled for peace of mind. Sounds like you want to push the engine hard and the safe bet is to cross drill the crankshaft to prevent a rod bearing failure.

[Daryl Smith]

Irrelephant

[Mochi]

Mochi,

Isn't the Mondello rods and VG30 piston setup for the 2L stroker?
If so, you will need an H20 or U20 crank.....If using the U20 crank, you don't need to worry about crossdrilling....H20? likely.

I bought a h20 crank from mondello. He said it was out of a car.

[Daryl Smith]

Irrelephant