[mgarblik]

Originally Posted by Jay S

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.

[PAUL K]

Originally Posted by Jay S

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.

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".

[PAUL K]

Originally Posted by 25stevem

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?

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.

[PAUL K]

Originally Posted by mgarblik

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.

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.

[Elarson]

Originally Posted by mgarblik

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.

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

[PAUL K]

Originally Posted by Elarson

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?

[Shiny]

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.

[61-63]

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.

[PAUL K]

Originally Posted by hurryinhoosier62

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.

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.

[mgarblik]

"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.

[Jack Ferris]

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.

[mgarblik]

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.

[Jay S]

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.

[Sirrotica]

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.

[Half-Inch Stud]

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.

[25stevem]

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 .

[hurryinhoosier62]

Originally Posted by mgarblik

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.

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.

[Jay S]

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

[Steve C.]

"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.


.

[mgarblik]

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.