GM Ford Mopar cast iron crankshafts.... Do they fatigue?

[bigmike]

Does something like a GM cast iron crankshaft fatigue like say a GM steel crankshaft. Reason I ask this is I've seen a fair amount of broken GM steel crankshafts over the years (especially from circle track cars) but can't think of any broken GM cast iron crankshafts I've seen. Seems like there is more than a few people that think nothing about running a GM cast iron crankshaft in some of the lower classes. Than I got to thinking about years ago when everyone was getting cast iron high milage 400 crankshafts turning down the mains and running those in steet / strip cars some well into low 12 second cars. Some for a few years plus with many passes down the drag strp. Can't recall any of those breaking crankshafts. Not talking about China made stuff but good old American made cast iron GM / ford / Mopar stuff.

[rustbucket79]

I've seen more than a few 455 olds cranks (cast) with cracks in the rod fillets. Used a number of cast 350 cranks in asphalt oval track applications (2 bbl) and found they will start to crack after a couple of seasons depending on the lap counts they run.

On a personal note, ran a stock 400 Chevy crank in a bracket car for 2 seasons external balanced, then decided to grind and internal balance ( 6 slugs of mallory) another 400 crank and on the off season found cracks.

[lefty o]

cast iron cranks will absolutely fatigue.

[blykins]

Yep.

Built a 400 Pontiac for myself as a dyno mule, made 600 hp on the first pull and also spun a rod bearing because of a crack in the rod journal. Crank had been magged before it was ground.

Also had a Scat 9000 series 3.400" crank in a 347 bracket engine. Engine went 8 years without a freshen-up, finally had to pull it down because he had been running with a blown power valve and washed the cylinders down. Magged the crank and it had cracked as well.

[pamotorman]

cranks with cold rolled journal filets are stronger. google it.

Crankshaft deep rolling




Deep rolling is a method of cold work deformation and burnishing of internal combustion engine crankshaft journal fillets to increase durability and design safety factors. Compressive residual stresses can be measured below the surface of a deep-rolled fillet. Other types of fillets on shafts or tubes can also benefit from this method. Cast iron crankshafts will experience the most improvement potentially doubling their fatigue life. Typically the crankshaft is machined with under-cut fillets as opposed to tangential radiused for ease of manufacture, although all types can be deep-rolled. Most automakers are currently utilizing this crankshaft technology including: General Motors LLC, Ford Motor Company, and Fiat Chrysler Automobiles (FCA) The North American-based Hegenscheidt-MFD Corporation in Sterling Heights, MI, was established in 1966. Ingersoll CM Systems of Midland, Michigan with Global HQ located in Dalian, China and European based SPMS in Évry, France (established 1974), are the only major machine/tooling manufacturers of this application in Europe and North America, supplying a highly specialised product throughout the global manufacturing sectors.

[SupStk]

cranks with cold rolled journal filets are stronger. google it.

Crankshaft deep rolling




Deep rolling is a method of cold work deformation and burnishing of internal combustion engine crankshaft journal fillets to increase durability and design safety factors. Compressive residual stresses can be measured below the surface of a deep-rolled fillet. Other types of fillets on shafts or tubes can also benefit from this method. Cast iron crankshafts will experience the most improvement potentially doubling their fatigue life. Typically the crankshaft is machined with under-cut fillets as opposed to tangential radiused for ease of manufacture, although all types can be deep-rolled. Most automakers are currently utilizing this crankshaft technology including: General Motors LLC, Ford Motor Company, and Fiat Chrysler Automobiles (FCA) The North American-based Hegenscheidt-MFD Corporation in Sterling Heights, MI, was established in 1966. Ingersoll CM Systems of Midland, Michigan with Global HQ located in Dalian, China and European based SPMS in Évry, France (established 1974), are the only major machine/tooling manufacturers of this application in Europe and North America, supplying a highly specialised product throughout the global manufacturing sectors.

Sounds like an ad from an equipment maker.
Back to the OP, yes cast cranks have a limited service life in performance applications. If a person magnafluxes them periodically and scrap them when cracks are following the radius, they can be used successfully in fairly high power engines.
With affordable forged cranks available for most common applications, I don't use as many cast cranks as I used to.

[dfarr67]

I think in a certain application where the owner spec's a forged crank knowing the abuse it's going to get- you going to see more failures in that segment.

[Carnut1]

A friend once gave me a tbi shortblock out of a suburban. He said he thought it was developing a wrist pin knock so he changed it out. The cast crank came out in three pieces. Thanks, Charlie

[SupStk]

A friend once gave me a tbi shortblock out of a suburban. He said he thought it was developing a wrist pin knock so he changed it out. The cast crank came out in three pieces. Thanks, Charlie

I've seen the same thing.
Once bought a back row beauty off a car lot. Salesman said it had a busted crank and fired it up. Sure enough sounded like it so bought it cheap. Had a spare 350 sitting in the shed. Began pulling the engine starting with the converter bolts. Noticed the cracked flexplate. 40 minutes later it was purring like a kitten.

[pdq67]

Didn't the 3.8 L turbo Buick engine have deep rolled cast cranks in them??

pdq67

[billet]

I can tell you from experience in circle track a stock SBC cast crank doesn't break anywhere close to a Stock SBC steel crank does. I've seen so many steel cranks break it's not funny, but rarely did a cast one actually break.

We used to get un-raced cast cranks and after 1 or 2 seasons when zyglo tested for cracks you would see a ton of very small cracks forming all over the place. Usually I could go 2 seasons on a crank, turning 8400 RPM and it would show cracks so you just replaced it. It was way cheaper using a 25 or 50.00 cast core then buying a 200.00 steel core that probably wasn't going to pass the zyglo test and would break before the season was over. I never broke a cast one, but then again I was checking them but can't say that for a steel crank.

I really think, it has more to do with the twist back and forth of the crank from hard acceleration and then to engine braking twisting the crank the other way 2 or more times a lap. No science there, just some common sense but that could be wrong as it usually is, lol.


I should add the zyglo testing that was done was a place that tested aircraft parts and was told they looked at the part with a microscope (not sure that is std with zyglo testing or not) but pretty sure regular tests would not show these very small cracks. I was told they could tell if the crank had ever been raced just off this and these would never show in a street crank. We just replace them once they go so bad, just for insurance.

[pdq67]

I have read where those multi-keyway steel crank timing sprockets can kill the snout of a crank.

Anybody else hear/read about this happening??

pdq67

[Mark O'Neal]

cast iron cranks will absolutely fatigue.

And, if they're in a 400M, they'll do it remarkable vim and vigor. Maybe even a bit of verve.

[Mark O'Neal]

I have read where those multi-keyway steel crank timing sprockets can kill the snout of a crank.

Anybody else hear/read about this happening??

pdq67

Only if you use the wrong slot.......

[SupStk]

I have read where those multi-keyway steel crank timing sprockets can kill the snout of a crank.

Anybody else hear/read about this happening??

pdq67

Any sprocket will kill the snout if there isn't enough radius to clear the crank fillet.