Nodular Iron Cranks

[1972ho]

Racer that run stock eliminator ford clevelands run the engines up to 7000 to 8000 rpm year after year and don't break cranks and most are external balanced.

[groberts101]

Racer that run stock eliminator ford clevelands run the engines up to 7000 to 8000 rpm year after year and don't break cranks and most are external balanced.

yep. plenty of Chevy guys doing that too. it's all in the prep and tuning consistency to keep them alive.

[BOOT]

Quality damper

[lada ok]

A friend of mine worked for a pro stock team back in the 1970's and they ran production cranks in their Ford engines. Turned to a 2 inch rod thow and de stroked to 3.400 they launched the car at 10,500 rpm and turned about 9500 or more the rest of the pass. When we were talking he told me that he couldn't remember ever breaking a crank. They probably made 700 or so horsepower...

I don't know if Shelby and others would agree with that

[Walter R. Malik]

A friend of mine worked for a pro stock team back in the 1970's and they ran production cranks in their Ford engines. Turned to a 2 inch rod throw and de stroked to 3.400 they launched the car at 10,500 rpm and turned about 9500 or more the rest of the pass. When we were talking he told me that he couldn't remember ever breaking a crank. They probably made 700 or so horsepower...

I don't know if Shelby and others would agree with that

Did SHELBY ever drag race Pro Stock...? He was a master marketer, that's for sure.

[pdq67]

I did not know back then that I could walk in off the street and order a new Cobra OR I would have!!

pdq67

[user-23911]

Even stock cranks can fail randomly.
Over the last few years I've seen first hand 3 different cast steel cranks break into 2 parts.
All Japanese diesels, 4D56, YD20 and 4JG1, from Mitsubishi, Nissan and Isuzu.
The Isuzu, it started to crack at the radius of no 4 bigend pin and just got bigger until it was 2 pieces.They still run, just make funny noises.

On the other hand I've seen an LS1 crank (cast iron?)it had an oiling failure, spun 7 big end bearings, got hot and ended up with a massive bend in it, most of which was in the nose between the bolt and the no1 main bearing.

[Dan Timberlake]

Like any casting, there will likely be material variations and defects thruout the part.
the sketchier the source, the more likely there will be chills, defects, and zones of unintended metallurgy.

Forgings are not immune to defects, but the forging process tends to "correct" some of them.

I'd check out any part I was concerned with, even if it was brand new from a supplier with a great reputation.
1 - Visual inspection of all fillets with magnification and bright light
2 - Magnaflux ( wet method fluorescent ) . Cranks can be effectively magnafluxed with a single magnetization. Other parts require multiple magnetizations in different 'directions"
3 - straightness/colinearity/runout of main journals, flywheel pilot, flywheel flange, rear main seal surface, sprocket seat diameter and shoulder face and snout.
4 - Rod and main journal sizes, taper, roundness, rod journal width, thrust bearing width, journal finish


Once the basic part is sound, and the geometry is good, shot peening the critical areas can buy SIGNIFICANT improvements in fatigue life by jacking up the useful fatigue strength 10 to 30%. Cracks happen when loading creates alternating stresses that exceed the materials fatigue strength. It would take a heck of a material upgrade to iimprove fatige strength 30%.

[BigBro74]

I am no closer to finding the answer to the original question by OP. I have used several scat 9000 cranks-all in 2bbl circle engines (probably 450hp/7000 ish)- and have yet to have one break despite several mishaps on the track. BUT I always try to get the racers to buy a forging- it is on them then!

one of the racers told me- " I just saw a 2000$ crank laying in pieces on the track a half hour ago, could happen to anything being raced"...........

one of those scat replacement 350 cranks in the garage R/N with 3000 laps on it, and it is going back in the engine for its 4th overhaul.

stock block may give out b4 the cranks?

IDK- damned either way- stuff breaks!

[Schurkey]

Like any casting, there will likely be material variations and defects thruout the part.
the sketchier the source, the more likely there will be chills, defects, and zones of unintended metallurgy.

"Zones of unintended metallurgy" is a beautiful phrase. It explains many cases of Sudden, Terminal Disassembly. Thanks for that.

Forgings are not immune...

Thank you for the post, and for the attachments. Most informative.

[barnym17]

The truth is you can break anything if ya try, that said I prefer stock cranks my reasoning besides seeing several broken aftermarket cranks when dirttracking is dead simple,GM, Ford, Mopar spent millions engineering their cast cranks which they had to warranty under conditions ranging from grandmas car to overloaded dump trucks with junior racers dumping the clutch with tons in the bed rolling backwards down a grade and they lived. Scat and Eagle I doubt put in that much r and d and they dang sure don't plan on warranting them for 100,000 miles like oems did with their version.

[user-23911]

The answer is quite easy really.

The best quality parts are OEM.

Most aftermarket stuff is rubbish.

Go buy yourself an aftermarket crank....measure it up.
Then put it into the crank grinder and fix it?

[Steve Haaf]

Cast steel cranks are bought and used for their economic facture and available length of strokes. Nothing more then that, they`re cheap and easy to get. They are bought to build engines that will make more power then a stock engine will, but they do have their limits. How much do you expect out of something that you only spent maybe 250 dollars on and then put some old beater dampner on it. I`m with Boot on the thought that putting a good dampner on the crank will allow it to last longer at a certain power level. I know it`s hard rationalize putting a dampner that costs as much or more then the crank your putting it on, but that maybe the only thing that allows the crank live when it starts doing a hola dance at 6 grand plus. Yes, you have to put a lot of extra work into a crank that has to be stock and that is going to be raced hard but to do that on everyone, that`s just not marketable. There`s thousands of cast steel cranks are out there working right now and they`re selling them every day, it`s just how much can we expect of them. I`ve read articles that advised a 500 hp limit. They just never say how to get them to live at that level.

[DaveMcLain]

It is a well known fact that many Ford 351C NASCAR engines were built and run using the factory cast crank which was then replaced after each 500 mile race. They were turning it over 7000rpm for 500 miles and probably making in excess of 500 horsepower. What sort of preparation was done to those cranks? Anything special?