Factory cast crank experiences
 

Curious what issues or success stories folks have had with factory cast crankshafts.

I've seen one break in two pieces. It was the later style crankshaft that was in a 76 455 four speed Trans Am that I doubt was making 300 horsepower. The outer ring on the harmonic damper had slid back towards the timing cover and was rubbing against it. Generally, the car seemed like it had seen a lot of harsh driving. I figured the damper becoming non-functional and one too many power shifts led to the crankshafts demise. The engine was still running but made a bunch of noise and shook a lot. This was the only factory crankshaft failure we have seen first hand.

Attached is a video show casing that crankshaft

https://fb.watch/h-fC5Pks-W/


On the other hand, we have been successful using factory crankshafts. We've made close to 1100 horsepower using nitrous oxide. We've built belt driven (8-71) supercharged engines that have seen many years of service in the 800-900 horsepower levels. We've routinely shifted them over 7,000 rpm, buzzed them through the traps as high as 7600 and they have held up without any issues what so ever.

I'd like to hear other folks experiences.... good or bad?

I’ve pounded on cast factory cranks, my 2 bolt main cast factory crank turbo car has lasted forever, much of it is in the tune, but all my N.A. stick cars had cast factory cranks except one w a RAV forged .

I’ve never had a crank failure . I had one aluminum rod lose a fowl pin and cut into a crank but it was a forged RAV. All my cast factory cranks survived un hurt even at 960 Hp.

Rods are the weak link typically. I’ve throw rods spin rods, cracked a cyl . But cranks have been rock solid. . The filet area is important prep on a Pontiac crank.

I think it was in McCarthys book where he said he has seen less Pontiac cranks fail than he could count on one hand. Something like that.
I beat on my 30-30 455 crank for 30 years.
When I put a 4" crank into my 455 block it will be a PMD 428 crank. Steel crank will get me no advantage other than lightening my wallet.

Paul with how small the amount of failures to be read about on this ( and you have to search ) and how nice your success is with them when prepared and balanced right and run in a motor that's tuned right, I am very curious as to why you have even started this thread?

Actually this is a good thread. I will use this info for my next build. A 440””use a new forged or turn down a factory 428 crank.

I am not at all saying it’s a useless thread, as I asked I am interested in Paul’s reasoning.

Pretty sure he spelled it out in the original post.

I'd like to hear other folks experiences....

Seems pretty clear, no?

There was a guy on here w an aftermarket for fed brand new w a hole in the journal (not an oiling hole) I personally just bought a butler stroker forged crank for a build and it’ll be the first aftermarket crank I’ve ever used in my own engines. I’ve always used factory cranks and been very happy. Belive that aftermarket w the hole was from molnar but do a search and see .

I guess what I am asking is if he is starting to get a bit white knuckled at the power levels he has been safe with so far?

Both NA and Boosted based PMD cranks follow the Goodman Diagram. I think the NA powered Cranks last much longer.

My boated crank has been fine and I get cap walk

Paul the one in the current 455 in my 78 was in the same block different configuration racing NMCA with teh RAIV heads. Car had a jack under the front crossmember slipped off and caught on harmonic balancer. A couple of months later in the staging lanes balancer that was on the crank let go crank spinning it in pulleys not moving -probably cracked it. Crank still doing great and a lot of passes the past 20 years since then and more HP put to it. Just not a stock cast iron balancer.

As far as the cast cranks from PMD and failure in my own experiences, I've never run any crank in my Pontiacs other than a cast crank. So the only thing I've seen break one is when a rod breaks off, and the flailing rod gets between the block, and the rod throw. That includes from a 326, to a 400, which all use the same basic 3.75 stroke crank. I've also run a slew of the large journal cranks in racing applications, 428, and 455 cranks have not failed, unless an errant rod gets in their way.

I believe that the engineering on the Pontiac cast cranks was so over engineered that the sheer mass used in their construction made them far stronger than any other major manufactures cast iron cranks. Smokey Yunick eluded to this over engineering when he appealed to the engineers to reduce the size of the main journals of the 421, years later after his statement it's been pretty well proven fact that the cranks will still survive without the excessive overlap from the main journals, and the rod journals. The engineers had a formula that a certain percentage of overlap was need to assure longevity of the cast cranks.

Anyway I've run cast cranks in small main journal engines as well as large main journal engines for season, after season, on a dirt track without failures. Some were prepped, and magnafluxed, some were run just as the factory sent them out the door. The only Pontiac cranks that I've seen break under just normal driving were the 301 cranks, that cut too much mass out of the cranks it made them weak. The same engineers that engineered the large overlap on the 421 cranks would have been spinning in their graves when the 301 crank appeared.........:eek:

Anyway those are my experiences over more than 50 years of wrenching on them, and racing them. I hope that my experiences can give you some background on the information you're seeking.

One other thing I'm aware of in the cast cranks that GM used pertaining to the harmonic balancers. On the GM/Detroit Diesel 6.2 and 6.5 engines, which also use cast cranks. If the harmonic balancer fails (common problem) and you don't catch it quickly, or just ignore it, the cranks will fail, and break pretty quickly. Of course gas engines, and diesel engines have much different harmonics acting on their cranks.

GM would have been money ahead had they choosen the Pontiac V8 to convert into a diesel, rather than the olds gas engines, The early olds 5.7s diesels had crank snapping problems when they first debuted in 77, and had to re-engineer their cast cranks to withstand the diesel torsional twist.

Well, I think PMD cast cranks are stronger than PMD blocks so there is no reason not to use one with a stock block most of the time.
Its a good thread and topic.

I have had a couple check cracked after being in service a while. In my opinion they are very durable but are still a cast part with about no radius

I have never had a cast N crank break or an Armasteel crank break in my older 421 days. They have just been very dependable. Possibly just incredible good luck, I don't know. The N cranks we ran in the Grocery Getter drag engines in stock block 455's. Made around 1000,1100 HP spraying the heck out of them. Aluminum rods, extra wide fillet radius ground in, 2% overbalance. 5 billet main caps. We broke 3-455 blocks all in the same place up through the #2 main oil feed hole up to the cam tunnel. Never failed a crankshaft. I know they do break every now and then because I have seen pictures posted here.

I've ran a 428 and 455s with stock cranks. Probably around the 625hp level. Never had a crank failure. The only crank that I ever broke was attributed to a stock rod failure in a 467.

Mike, I think you have hit on something that will extend the life of PMD cast cranks: lighter reciprocating mass, proper balancing and a generous radius on all the crank journals. Any weight you can remove from the reciprocating mass lessens the stress on the crank. Proper balancing keeps the crank from beating itself to death. A generous radius on all the crank journals strengthens the journals, helping the journals not develop cracks which can lead to crank failures. I haven’t reground a PMD cast crank that I didn’t regrind the radius on each journal. 6.2/6.5 cranks are well. For some inexplicable reason GM wasn’t overly concerned about the radius on crank journals unless it was a Hi-Po BBC forged crank.

The wife fillet radius is how I’ve always made mine live . It makes a HUGE difference.

As I recall the only differnce w the SD cranks were the radius Vs the same part number regular 455 cranks??

Most the factory Pontiac cranks I have seen broke in the same place like in Paul’s FB video. Thru the throw just inside the RJ. If it was something with the dampener it seems to break on the front throw right behind the number 1 main.

It seems like takes a smaller RJ diameter to get a very good fillet there that adds much strength there. I think it would have still broke.


It seems like it is fatigue life that breaks them with a mix of street driving and racing more often than big HP racing. It is hard to catch them before they fail because they do not start small cracks that you can inspect or mag, they hit the fatigue limit and just completely let go. About all the examples I can think of that broke cranks were for street duty. Lee has broke a 400. Jim Hand lost one his first 455. Mchell broke one in his 455 not that long ago. I can think of a few that broke that had some welding done. Steve C. had one the broke. You don’t have to look very far, they are all on this board. Another member broke one like the one your working on Paul, but the crank snout and dampener ended up in a road ditch, along with the front block webbing.

These are all good points to consider. A street or street/strip crank isn't going to be removed and inspected on a regular basis like a race crank. A cast crank would be more likely to suffer a catastrophic failure than a forged one due to material and production process. Chinese forged cranks were not available when we were racing high HP Pontiacs. It was stock cast or billet only. Building a HP engine today, I would use a properly inspected and prepared forged crankshaft.

Can you elaborate on these? Off the top of my head I remember Steve C found his Crower forged crank to be cracked when he was fixing something unrelated. I recall Jim H breaking his and determining it was caused by "fatigue".

I'm hoping the information will be archived here and help other folks in the future. I probably should've posted it in the "street section" as they are the guys most likely to benefit from this information. However, I figured we wouldn't get input from guys that have had success using a factory crank and making relatively "big" power.

Most of the folks I work with have some kind of budget and are always curious as to "how much" something costs. The part I have a hard time understanding, is upgrading to a forged crank "just incase". As most of us know there are no guarantees, but to me it seems like an expensive insurance policy for a 550 horsepower build. I also feel since most engine projects have some type of budget, the money could be spent more wisely elsewhere.

Something I'm sure you can relate to: many years ago I ported a pair of SBF Ford heads for a guy. I charged him $650 and he wasn't really sure if he should be sending that much money for "porting" in his quest for a quick street/strip Mustang. But he proudly showed me his $300 Billet valve covers when he picked up his heads.... It just didn't make sense to me.

I'm not suggesting folks don't have the right to spend their own money how they want. Also with the supply of good 455 blocks and cranks this thread is probably a few years to late. But if you have a nice 455 block and crank most of the time you will be money ahead by using it and with the dough you save a really nice pair of Billet valve covers can be purchased.

Thanks for your input on this. I was hoping you'd talk about the Grocery Getter's experience. I think that says a lot as far as the durability of the Pontiac crankshafts.

I'm always curious what "caused" the failure. Not long ago, I took in an engine from another shop that did everything but complete engine builds. They gave me a freshly ground .020/.020 455 crank and the journals had no radius whatsoever. Zero, it looked like they deliberately ground the crank to make it a sharp 90°. I'm pretty sure the crank would've failed in short order and most folks not knowing the story would just blame the factory crankshaft as being weak.

It's great have choices between factory and 16 month wait Billets at $4k a piece. I recall many years ago, Dave Johnson's White Warrior (RIP) hunting down a 990 crank and bending it almost immediately.

To add a bit more understanding....

Cast iron is very strong but somewhat brittle.
Brittle material is very susceptible to stress concentrations in corners...big fillets are a huge benefit!
Brittle material is very susceptible to impact loads.....aluminum rods add some important cushioning effect.

Forged/billet steel is more ductile and therefore more forgiving of stress concentrations, impact loading and random abuse.

Eric

Eric would one material have a tendency to flex more underlies with all other things being equal?

Others' experience can help you bound the risk but compare your apple to someone else's, not to their orange. The more detail, the better you can judge.

IMO, once you exceed factory stress levels and usage models (load, rpm, time) you are rolling the dice.

I expect Pontiac engineers kept the max stress below the fatigue (endurance) limit of the material, effectively eliminating risk for fatigue failure. They could even have had the luxury of adding a safety factor.

But once you push the stress above that endurance limit by raising the HP, modifying the piston/rod weights, or exceeding the max rated rpm, the crank will eventually fail. Like HIS shared, how long it takes depends on cumulative history of time and stress levels (Goodman diagram).

So when you share your broken crank experience, the more detail about the application and use history, the better others can compare.

Someone may have mentioned this above and I missed it but Pontiac/Olds cranks were way over engineered. FE Ford cranks have 2 3/4" mains.

Agree, prep work is critical along with proper design. Back in the day we would turn down the counter weights quit a bit and make up for the removed material with slugs of Mallory. We would always stroke the cranks to increase the radius. Also back then shot peen, heat treat or hard chroming the journals seem to help with bearing wear. It's interesting the Chinese forged cranks showed up around the same time all the other procedures became to cost prohibitive to perform.

"It's great have choices between factory and 16 month wait Billets at $4k a piece. I recall many years ago, Dave Johnson's White Warrior (RIP) hunting down a 990 crank and bending it almost immediately. " Paul K

Many years ago, probably late 1990's, we had the opportunity to buy a 990 crankshaft. It was raced by Hubert Platt? (SP). Arnie Beswick tracked it down for us and we bought it. It magged OK and looked to be in good shape. We put maybe 20 passes on it in the Grocery Getter no issues. During a routine re-fresh I magged it expecting to find nothing. But It had developed multiple cracks radiating from the fillet area inward on several crank throws. We retired it at that point and sold it for a couple hundred bucks as a conversation piece. It was an expensive lesson in using 50 year old race parts. As much as I hate using Chinese parts, having a source for NEW forged crankshafts is a wonderful thing. IMO, the best of both worlds is a Chinese crankshaft raw forging, inspected and finished by a reliable and trustworthy company like Molnar. Other than a billet at 3X the cost, I don't think you can do better than that right now.

I ran a factory 103 N crank in my 740 hp 482 for years and at least 1000 passes. It was done decades ago by Crankshaft Specialist. It's offset ground to 4.250 with 2.200 RJ. When I parked the car in 2011 the engine went on a stand. Last year the same shortblock, with fresh bearings went into my friends bracket car where it's still being raced but in a detuned state. That's one example out of a few, but I've never had any issue with any other cast cranks.

Crankshaft Specialists was an excellent shop and we had a few cranks worked on there with great results. Finding a competent crankshaft grinder who can even get the correct diameters on the journals is nearly impossible now. The 2 shops I used the last 30+ years are closed, and the experts retired. I do not have a crankshaft grinder available nor the skills to operate it. It's one of the few things I have so farm out. In the entire State of OH, there is only 1 reputable source. That is Shaft Tech in Northern, OH. About a 3 hour drive but you do what you have to do. The only other shop I know is really good is Mile High Crankshaft, in Denver. Dave is just fantastic. The work is 110%. But $300.00 shipping round trip from OH. So for basic re-grind for a street engine, awfully expensive. Proper crankshaft grinding by a skilled professional is a lost art. Right now I have a cast crankshaft for a student's 400 Pontiac at a local shop. They tried 3 times to just do a simple re-grind on it. They finally ruined it and it is a throw away. He has crankshaft #2 now. Simply want the crank ground to a specific dimension for proper bearing oil clearance, straight and round. Seems to be beyond their capability. Fingers crossed.

We had a 455 years ago in a dirt track stock car turning 5 to 6000 for 1 season, on a dry track it would hit 6500 at the end of the straight. It thru 3 rods in a race midway into the next season. I watched it run 3 laps like that on a 3/4 mile track before he drove it on the trailer. I thought for sure it was toast. Not sure how he could hold on to the steering wheel with it missing 3 slugs, it had to be vibrating violently. We tore it down and mag’d the crank and it wasn’t broke, so we had it reground and ran in again. It went in 2 more engines, eventually cut down to 3” mains and bbc journals. We eventually decided it had enough and took it out of service.

Steve C has broke 2 cranks. One is Crower billet broke in the fixture like you said Paul. The other was a cut down 455N crank that had the thrust welded. I think the N broke in a couple places and mortally wounded the block. If I recall right it was still running fine and they caught that on a tear down inspection.

Jim Hand had a lot of passes and street driving on the one he broke, most of the time it was running 13s to low 12s in his wagon. It was before he was running 11s if I recall correct, if he was in the 11s when it broke it was just starting to run there. It was also in one of his brothers cars for a short time before that with a small shot of NOS. Can’t remember for sure, but seems like it was in a Can Am then?

There are threads for the other couple I mentioned, Mchell’s wasn’t that long ago. I will look and see if I can find links, they are in the street section. I thought the most insane failure was the one that sent the dampener, and front of the block into the road ditch with the front of the crank attached yet. I can’t remember who’s engine that was though.

With moderate power, forged cranks seem like they will run with cracks for a while. A Billet crank will allow more twisting yet, but have a shorter fatigue life than a forged. Cast cranks with good metallurgy can darn near take the abuse of a forged crank when new. Those examples like the grocery getter and those other big HP engines reinforce that. But comparatively, they probably won’t last as long as a forged because can’t take the twisting like a forged or a Billet.

I have a 455 crank reground by CS, in Memphis, done in 1988, everything was dead nuts on when I measured it. the finishes were as close to perfect as you'd ever want them to be. At that time I sent it by Greyhound, and it still was fairly expensive, but worth what I spent when I got the finished product, and everything was correct. I didn't have to swap bearings etc. to get the clearances right, standard .020 rods, and .010 mains fit perfectly. What a shame that they're still not in business.

I still have the engine assembled in my garage, and I'm goin to pull the pan, and check the bottom end before I put it into my next street car. When I built it in 1988 it was a standard bore with low miles, so it still has cast OEM pistons, and stock rods in it. Basically a stock bottom end with that really nice crank in it, and ported 5C heads, mild camshaft.

Hmmmm, the PMD 455 N crank may fail MAG due to cracks found in the rod journal armpit, yet I only seen broken cranks at the #2 Main. Usually due to a loose Damper.

I have some definitive disagreements with some of what’s been posted and or alluded to hear in this string.
1) a Billet has a long way to go before it’s as strong and as durable as a non twisted forging, since a billet does not have grain running the optimal way through out its make up .
2) besides the crank being far less likely to crack when a nice radius is ground from a journal to the cheek, the proper phasing of the weights on the crank can reduce loads by thousands of pounds which is critical to the life of 2 and 4 main .

Mike, I have ONE guy I trust to grind my cranks. I’ve known him for over twenty years. He does grind the rods and mains on spec and the throws are always on stroke. PM me if you need his phone number. His shop is about 35 miles from my house.

If you ever do break a crank. Don’t reuse the harmonic balancer.

"Steve C has broke 2 cranks. One is Crower billet broke in the fixture like you said Paul. The other was a cut down 455N crank that had the thrust welded. I think the N broke in a couple places and mortally wounded the block. If I recall right it was still running fine and they caught that on a tear down inspection."

Jay is correct.

The first was a 455 crank modified for my original '70 400 block. It went into service in Feb 1998 (626 hp at 6400 rpm). The engine was running at the time we found the damaged crank and damaged block.

The second was a custom Crower 4.250" billet crank made for my current 505. Its first dyno session was in March of 2007. In April of 2018 we had to tear down the engine for an bearing issue and found the crank bent. When the machine shop tried to straighten it the crank broke. It was replaced with a SCAT 4.250" forged crank that I bought from Paul.


.

When racing the Boss Bird Nitro engine, we ran Crower 4.25" stroke Billets. When trying to sort out the main bearing issues and oiling system in general, we bent the heck out of those poor cranks, especially the nose. We had bends at times in various locations of nearly .020"! We had those cranks straightened at least 3-4 times each, and right back in the engine for some more abuse. Never a crack. We simply couldn't afford to replace them. We were bending them every time out for a couple years. When we finally got the oiling system sorted out, no more bending. I guess I am surprised to hear of a billet breaking like that. Not questioning it happened, just surprised. The billet cranks seem to have a memory as well. Once bent, they seemed to bend easier the next time, until they were happy in the engine. In our case with the nitro engine that meant .0065" main clearance and 140-160 PSI oil pressure through the entire run. 43 GPM oil pump.

The aftermarket cast cranks have a generous radius and are usable out the box for the most part. If a Experienced grinder is not available in your area they do well.

I looked at a lot of broken stuff back when I designed PMD main girdle’s, looking for failures and trying to figure out what some of the causes were. Too me it looked like a lot of the crank failures had too do with bad harmonic balancers. I learned the hard way a long time ago moving the same balancer to a blown engine and had the problems follow the balancer from engine to engine. It why I mentioned not to reuse a balancer from a bad crank, found out first hand it is a bad idea.

Here’s another failure I recall that broke a crank. Member HO428, I think he was road racing.

And another memorable one. I think this one also may have been a dampener failure. But could be the main saddle failed first, it is hard to say for sure. This one was in street driven 3.75 stroke 041 cam combo. It was a 557 block with ARP main studs. Don’t recall the member.


Forged crank should handle harmonics a lot better than a cast crank if the dampener doesn’t do it’s job. Billet should be better yet, for at while at least. A bad dampener will kill about anything given enough time.

Even in a controlled fatigue test of machined test coupons, the variation in cycles to fail under identical conditions is huge. Say you test 100 parts and the first fail happens at 1000 cycles... the 100th sample to fail might take over 1,000,000 cycles. This is the nasty truth about fatigue failure.

Now imagine you all have the same engine in the same car on the same dragstrip. The first crank could fail after 100 passes. The next might go 500. Another might go 3000.

So yes, you could be lucky or maybe you weren't even close to failing. But if you see one break that is close to your build and usage, I would wonder if yours is special or just that 99th percentile crank.

I have a fresh ground Crankshaft Specialist crank. I will take some pics of the journals and get it up. The radius's were quite large from what I remember. Have not opened the box in years.

Jay / guys, I have seen two blocks fail like that .
The first one was years ago at a local machine shop that use to be handy and close.

The second was just this passed Summer at a junk yard that was trying to clear out to shut down.

I took the time to pull the pan off the 557 block even though the timing cover was blown off the motor.

The interesting detail that clicked when a saw this second dead block was that the crack that started the main bulkhead failure looked like it started right at the crank centerline side of the dowl pin hole, which was what I thought was the same starting point on the first failed 557 block I ever saw.

I have seen pictures of one of these block failures that very clearly started at the sharp edge of the drilled main bearing oil feed hole.

These blocks are just too weak to stand up to anything but a well balanced recuperating assy and a good tune.

I should have taken a picture of this second block and crank, but my hands where too filthy to even think about handing my phone, lol!

Sorry, I did not really mean to side track this string.

Interesting discussion. I have broken two 103N cranks. The first was 1996. There was nothing left usable on the entire engine, except for 6 pistons I gave to someone else that I would never use and don't even know why he wanted them. I was young and found what I thought was the cause which was 11.5 to 1 on pump gas, so I assume the crank may have lived if I treated it right. It was an expensive lesson for a 20 year old and I learned alot. After that so many people tried to convince me to go Chevy. More recently in 2013 we had a 455 built for my neighbors lemans (now my buddy Marks car) . I bought that block and crank from another guy in 2005. It had been in his shed for 20 years prior. We had everything magged and everything passed. My local guy here, who I still use built it, We got the car running but he just never did anything with the car. This was 2013. The car sat until 2019 when he said he wanted to "get back into it". So we got the car up and running again but this time I heard a tick and thought maybe it needed to build oil pressure. We eventually tried everything, flexplate, trans you name it. The engine still had oil pressure. We eventually took the engine out and back down to my guy. Turns out the crank was cracked and he fixed it for free (labor) 6 years later. Now this crank was out of a big car in the early 80's, sat for 30 years, had 20 street miles with a few burnouts on dryrotted 14" radials. Is this fatigue? Coincidentally the same balancer was used but it is now on an eagle crank. I guess we should get that off of there? Sorry long post

Sorry for my cynicism, but Post 43 might have been ARP TQ-level induced failure. Agreed on the Damper culprit.

Custom 2-stroke unmanned aircraft engine busted the crank we made, during FAA endurance life testing. Professional metallurgy analysis showed the "SAE" 4340 steel billet (China!) has magnesium sulfide striations, that lead to early fatigue. Know thy Billet source !!

Factory PMD Cranks sound real good to me.

I found the thread for the 557 that broke. I agree it could definitely could have all been a crack from the dowel that caused that. What was odd about that one was one side of the saddle broke and left the other side when the crank broke. I have never seen one fail like that in one of the weaker blocks. That is about the only 557 I have seen that the crank may have let go first. Some others commented similar thoughts in the thread.

https://forums.maxperformanceinc.com...&highlight=557


About a year after Mchell broke his crank there was another thread with his new engine showing the timing marks on the harmonic balancer were off an 1” or 2”. It was an aftermarket balancer, I don’t know if it was the same balancer from the engine that broke the crank or not. Seems like too much of a coincidence though.

Interesting that you bring up Billet source. Tom V always makes a big deal out of material for crankshafts being real "Timken ball bearing steel" There is something to that for sure. The mention of the Crower Billet crankshaft breaking may have some tie in there. For a couple years, Crower broke with tradition and bought a quantity of Chinese billets. They made a good size run of Pontiac billet Pontiac cranks from this stock. To their credit, they sold these cranks for about half the price of their domestic sourced billet cranks. We bought 3 of them and had no issues in the nitro engine with them. But you just never know. Of the 100's of things to worry about in an engine that can fail, a broken crankshaft would still be pretty low on the worry list. A good harmonic balancer with a press fit to the crank nose, a premium bolt with 200 ft. Lbs + torque is a must on a performance engine. My balancer of choice for a serious engine build is ATI.