I found a new Machine Shop to Rebuild my "Rebuilt" 327 engine and took my 3951130 forged crank to them. (One part at a time to inspect them and rebuild if needed this time a round) The gentleman at the counter took my crank taged it and put it in the waiting room line with the rest of the cranks. He mentioned that it looked like it was a factory "Cross Drilled Crank" ?? I did not know what that meant so I looked it up and found lot's of negative write ups about the Cross Drilled cranks. So my questions are all SBC Forged cranks Cross Drilled? And what's really the Good or Bad news about the SBC cranks being Cross Drilled?? Thanks everyone for your support when I found all the problems with my 327 awhile back. I'm starting all over again and lesson learned with that other (don't like to call it that) machine shop and parts store with the four letters on that big square sign is now in my rearview mirror and lost in the cloud of my smoking tire's. Thanks again everyone for all your help it's very much appreciated... 1Nimrod
There are two methods of drilling a crank that look similar, but in fact are very different. Cross drilling a crank is old technology, and is not used in high winding engines.I would not worry at all about running a true cross drilled crank on the street but I wouldn't race one. The other method of drilling a crank is called straight shot drilling, and looks superficially similar to a cross drilled crank. You can tell if the crank was drilled this way by inserting a rod in the hole in the rod journal and notice that it goes directly to the main journal. This is a good method of building a crankshaft, and is used in many severe racing applications. I have a Chev 427 crank that I thought was cross drilled, but it turned out to be the latter modification, which made me very happy. Picture is an example of straight shot oiling, from Muscle Car DIY Bob
j-jock: I will dig out my pics of the crank with gun cleaning rods going in an out of the journals and post them tomorrow for all to see what I have. I took pics as I was checking to make sure the hole's had no gum/grease in them from my 1st so called rebuild. Sorry not able to post them right now. thanks 1Nimrod
Forged is better than cast, however David Reher from Reher Morrison doesn't recommend cross drilled cranks for racing purposes. In a street engine they may OK but they're not for serious racers according to him. I believe he knows a think or two about going fast and HP.
Are you guys sure about factory 302 Chevys having cross drilled cranks? I’ve never seen, let alone heard of one before. Anybody have documentation on that?
I have a 50+ year old factory cross drilled steel crank in my 427, it's been racing and driving a lot and I never though twice about it being a problem.... I guess if you're running on the ragged edge of reliability, you might want to worry about such things. Not many of us are.
The way it looks to me, is that your crank is not a cross drilled crank, but the desirable straight shot drilled crank. Like one of the other posters stated, cross drilling and grooving cranks are old technology, but even though they are, there should be no problem running them on the street and the occasional run down the strip. Here is a link to an excellent crankshaft article. https://rehermorrison.com/tech-talk-51-crank-calls-part-ii/ Bob
Cool thanks again for all the information everyone hope the pictures helped?? The gentleman that took it in was the owner's wife's Dad, he's part time help retired just helping with the phone and front desk work. I just found this out so he's not really up on these things and knows about as much as I do and that's just enough to get myself into trouble lol... 1Nimrod
I only found one reference to factory cross drilled SBC cranks and that was on the Nasty Z/28 website, here it is- "...... a crank is tufftrided it will have a dull grey color to it. Many cranks used in severe applications are cross-drilled, which helps ensure constant oiling to the main bearings. All tufftrided cranks are cross-drilled. Not all cross-drilled cranks are tufftrided." Sorry, but I'm still not a believer. I bought a brand new 1970 LT-1 short block on the pallet from Nickey Chevrolet BITD. Granted it was not a DZ 302 but the crank that is in it to this day was tufftrided but NOT cross drilled refuting what the above statement claims. A statement with no facts to back it up is meaningless.
a cross-drilled crank has 2 oil passages usually 180* apart. that provides oiling to the rods by allowing oil to enter the crankshaft at 2 locations instead of 1. it has to weaken the metal by having a hole completley through it. they used to also machine a small groove from the oil hole in the main journal 360* around the main journal to provide a better flow of oil to the rod bearings.
but Chevy engineers figured out a long time ago that you want full width journal and bearing, at least on the bottom side....they put a groove in the upper half, and the cross drilling means it is feeding pressurized oil from this half groove to the holes to the rods, all the time. If oil really moves that fast, that is
@1Nimrod, here is a sketch of how a crank is cross drilled, this hole straight across the main journal is what @squirrel referred to in his above post. I don't know a lot about BBC's but I think the first big block Chevy crank that was cross drilled was the 427 L-88. The cross drilling starts at the original oil hole for the rod journal as illustrated by the welding rods in the above photos. I wonder if some have a different perception of what cross drilling actually is?
I read what you posted just yesterday and much more but most was negative about cross drilling and wasn't sure if my 327 crank was Cross Drilled or not? I was also wondering if my 327 crank was tufftrided not sure by looking at the color but it was form a HD 1968 C20 or C30, I have that Big front all steel "U" motor mount that was bolted to the front of the 327 looks a lot like the old Hurst front motor mounts. Learning something new every day. My Pop's always said you never stop learning until your dead... 1Nimrod
Fordors: I think I see what ya mean now not down on an angle like my 327 crank but stright across the same journal?? 1Nimrod
Yes, but only straight across the main journals, the rod journals remain as stock from the factory. Give some thought to what @birdman1 posted and you will understand what the old reasoning was, but it was at the sacrifice of strength.
Fordors: For sure I understand now thanks. Is there any other way to know if my 327 crank was factory tufftrided or is color the only way? And if it does get turned down will that turning take off the tufftrided?? Thanks again everyone ... 1Nimrod
if it's still standard size and you don't need to turn it, it's probably tuftrided! like the crank in my LS-7 that has over 100k miles and still looks like new
The 302 turned allot faster rpms that the LT-1 did and went on to win 2 trans-am championships using that same crank .. Don't think the LT-1 was capable of spinning 8000-9000 on the street without blowing something up....
Until you can show something definitive than the factory cross drilled small block crank remains nothing more than an urban myth. Something tells me those cranks only came in the 010, 020 high nickel blocks.
squirrel: Thank You again it is still standard size but because of the light damage the other shop caused I'm not sure if it can be lightly cleaned up again to take out the little marks from the rod bolts hitting the journals? I'm hoping it will clean up with out turning down. I'm sure if it was not harder than the average factory cranks the damage would have been much worse so hopefully it will clean up easily? Thanks for all your help I really appreciate your response... 1Nimrod
The Jalopy Journal
