Anybody cross drilling their sbo crankshafts?

 

Nope

 

I had a machinist tell me it weakens the crank. Or is that more of a chevy problem?

 

The crank will be weakened very slightly, however cross drilling is normally a part of building a high power/high rpm engine so I guess the crankshaft usually gets toughening treatment at the same time if done by a good engine builder.
Why would you want to anyway?, Olds engines aren't prone to rod bearing trouble more than most other engines.

Unless you are building a competition engine I would leave well alone.

Roger.

 

Well that's what I'm building...

Cross drilling was a common deal when I was drag racing and stock car racing in the 60's.... somewhere along the line we quit doing it... not sure why. If I'm correct it seems the #4 and #6 rods in the Olds engine seem to have some problems with oiling...

I have read here, and other places, that the oil holes should be chamfered. Some even suggest making a "groove" in the rod journals to point the oil in the right direction. I would think drilling the crank would allow better oiling of the rod and main journals...

 

I don't cross drill. #3,6 rod spit holes come out at a bad angle, so I do run a short groove in the direction they should have pointed, and chamfer all the oil holes.

 

#3 and #6... OK. I'm going to talk to my crank guy and see what he sez... other than a slight decrease in strength I don't see how it would hurt. Sure would help with oiling i would think.

 

I've been referring to two excellent engine building books the last several months... one by Bill Jenkins and the other by Smokey Yunick... by any measure both are legendary engine builders.

Jenkins mentions all of his cranks are cross drilled... but the pix only show them drilled thru each main journal not drilled from the mains to the rods.

Yunick sez he wouldn't cross drill the stock forged chevy cranks he used... but he would cross drill any big $$$ billet crank. Not sure why but maybe to insure his investment?

In any event I think punching a couple extra holes in an olds crank may be a good thing.

 

I have a 455 from mondello 2-3 years ago and my crank in a big block was done this way and i have had no problems.

 

Some things just fade away... good or bad. Good to hear... thanks.

 

Those books are about chebby's

Get the book by "BTR" racing and do what he says
He is here a little or on "ROP"
his web site is "High performance Oldsmobile" do a Google search


Gene

 

The principles are the same whether it's a Yugo or a Ferrari... Yunick's book even mentions a few things about Mopar and Ford engines (mostly how much better they are than a SBC in certain areas) which I thought was cool.

Again... we used to cross drill 'em all. It was standard practice... Ford, GM, Mopar. I'm not campaigning to get anyone's approval on this but I'm more interested in the reasoning why it has lost favor.

My '65 Ford oval track 427 FE straight from Holman/Moody was drilled as was a used NASCAR "Hank the Crank" unit I bought for my 351-C.

BTW... I would recommend either of these two books for anyone who wants to learn about performance engines... Bill Jenkin's "The Chevrolet Racing Engine" and Smokey's "Power Secrets"....

 

I urge you to heed 64 Rocket's advice. There are certain important differences between a chevy and the Olds engines. With two bolt main caps on the Olds, you need to consider the opinions Bill Travato offers in his book. Cross drilling the crank is not really essential on the Olds. Why spend the money for work that does not make your Oldsmobile engine live longer or improve it? Clearances will also be a major issue for you. If you run Chevy clearances on the Oldsmobile you will be asking for trouble.

 

I agree, don't build an Olds "like a Chevy".

 

Don't know how 2 bolt/4 bolt comes into it... every engine I've ever run in dirt cars had two bolt mains except one 351 Ford and my old 427 FE. Most SBC running in the stock classes have two bolt mains, too.

I can drill the crank right here in my shop so it won't cost anything. Every engine I know of that has a pressurized system gets it's rod bearing oil from the main oil gallery that feeds the main bearings then it travels thru the passages in the crank throw to the rod bearings... that's all the same.

In an engine that has two rod journals that seem to have oiling issues (3/6) due to a poorly designed oil hole design, how can having oil lube the crank thru two oil oils hurt?

I raced for over 20 years... most every crank I saw that was used in a serious oval track race engine had a cross drilled crank... Ford, Mopar, Chevy... the works. For some reason guys stopped doing it on a regular basis and I have asked a lot of questions from many folks and no one seems to have the answer why.

It's one thing to build a mild drag engine that will see maybe four or six passes per weekend at 6,500 rpm's in a straight line or a street engine that may see 5,500 when doing some burnouts leaving the local cruise-in. It's another thing to build a similar mild SBO that runs 10-15 miles per night with the pedal mashed to the floor 75% of the time... and has G forces tossing the oil around in the pan. Lubrication is critical... I have seen first hand what poor lubrication can do to a crankshaft. When it comes to oil circulation to the bearing more is better.

I may just drill the cast crank I have and leave my see crank alone and see how it all works out.

 

If built correctly, Oldsmobile engine main bearings do not have an oiling problem, hence there is no need to cross drill the crank. The BTR book would be a good resource for you; but the choice(s) are yours.

Good Luck!

 

Last night I laid a crank in the mains (I was bored) and found something really screwed up... the front main oil hole is about 30% obstructed by a poorly drilled oil passage coming from the right side lifter gallery... the edge of the passage sticks into the path of the oil.

So tonite I'll hog out galley to allow full oil flow. When I get my new bearings I'll also slot the oil holes in the upper bearings so the entire oil gallery will allow oil to flow to the mains without any restrictions. Been doing some other oil related mods, too.

 

The mods to the main bearings that you will be performing are outlined in Bill T's book..the mismatch in the oil passages to the mains is well known by all of us who have pulled one apart over the years. As others have said, just be careful with the bearing clearances and you should be fine. Keep us posted on the build .

Danny

 

Will do...