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#1
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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? |
#2
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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.
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Happiness is just a turbocharger away! 960 HP @ 11 psi, 9.70 at 146. Iron heads, iron stock 2 bolt block , stock crank, 9 years haven't even changed a spark plug! selling turbos and turbo related parts since 2005! |
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#3
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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. |
#4
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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?
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I do stuff for reasons. |
#5
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Quote:
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. |
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#6
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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. Last edited by Jay S; 01-14-2023 at 12:48 AM. |
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#7
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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.
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#8
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I am not at all saying it’s a useless thread, as I asked I am interested in Paul’s reasoning.
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I do stuff for reasons. |
#9
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Pretty sure he spelled it out in the original post.
I'd like to hear other folks experiences.... Seems pretty clear, no? |
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#10
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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 .
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Happiness is just a turbocharger away! 960 HP @ 11 psi, 9.70 at 146. Iron heads, iron stock 2 bolt block , stock crank, 9 years haven't even changed a spark plug! selling turbos and turbo related parts since 2005! |
#11
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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?
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I do stuff for reasons. |
#12
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Both NA and Boosted based PMD cranks follow the Goodman Diagram. I think the NA powered Cranks last much longer.
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#13
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My boated crank has been fine and I get cap walk
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Happiness is just a turbocharger away! 960 HP @ 11 psi, 9.70 at 146. Iron heads, iron stock 2 bolt block , stock crank, 9 years haven't even changed a spark plug! selling turbos and turbo related parts since 2005! |
#14
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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......... 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. |
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#15
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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.
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Skip Fix 1978 Trans Am original owner 10.99 @ 124 pump gas 455 E heads, NO Bird ever! 1981 Black SE Trans Am stockish 6X 400ci, turbo 301 on a stand 1965 GTO 4 barrel 3 speed project 2004 GTO Pulse Red stock motor computer tune 13.43@103.4 1964 Impala SS 409/470ci 600 HP stroker project 1979 Camaro IAII Edelbrock head 500" 695 HP 10.33@132 3595lbs |
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#16
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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. |
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#17
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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
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Be carefull of the feet you step on today.They may be attached to the a$$ you kiss tomorrow. |
#18
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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.
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#19
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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.
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#20
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Quote:
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“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
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