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Old 01-13-2023, 11:05 PM
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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.

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Old 01-13-2023, 11:38 PM
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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.
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Old 01-13-2023, 11:55 PM
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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.
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Old 01-14-2023, 01:25 AM
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Quote:
Originally Posted by mgarblik View Post
.... Possibly just incredible good luck, I don't know......
I know they do break every now and then because I have seen pictures posted here.
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.

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Old 01-14-2023, 02:08 AM
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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.

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Old 01-14-2023, 07:35 AM
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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.

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  #47  
Old 01-14-2023, 09:09 AM
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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

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Old 01-14-2023, 09:45 AM
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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.


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Old 01-14-2023, 09:53 AM
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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.

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Old 01-14-2023, 10:34 AM
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Quote:
Originally Posted by Half-Inch Stud View 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.
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.

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Old 01-14-2023, 11:54 AM
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Quote:
Originally Posted by mgarblik View Post
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.


X 2

Crower stopped with the imported billets for a reason.

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Old 01-14-2023, 11:54 AM
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If I have something here wrong feel free to correct me. Crank materials Arma steel is suppose to have a tensile strength of 105,000 psi, and a yield strength of 85,000. Nodular iron used in N cranks and 103’s should be pretty close to that, certainly would not be higher.

A factory forged crank is usually around 110,000 tensile strength, 10 series metals, but with more elasticity than nodular or Arma. Not that much stronger than nodular but more resilient to flexing. Which is due largely do to the improvement in grain structure over the N cranks. The grain structure on modern Chinesium N cranks is generally pretty terrible. Some of the factory forged are also forged in twist forgings. On those each throw they have to turn the forging die, it adds some internal stress in the crank versus non twist. Not sure what an old forged Pontiac crank would be? I think they may be this category.

Most of the aftermarket cranks are 4340 non twist forged cranks, around 140-145,000 psi tensile, and 91,000 yield. The non twist die are suppose to make it more resilient yet because they are forged in one shot from different directions. The further apart the tensile and yield are represent more ability to twist and better memory. You can compare the numbers, it is quite a difference which typical forged. We can praise a old Pontiac N crank all we want or even factory forged, but the strength is really not that close to a 4340 non twist.

A billet is SUPPOSE to be 160-165,000 psi tensile strength with more flexing resilience to all the others, still in the 90s yield? A lot of that is the extra yield combined with the steel’s grain running in the same direction combine to let it twist more. But the long term longevity, fatigue life, is notably less than the 4340 non twist crank at some power levels. The grain structure of the 4340 non twist has some advantages. Some argue it is still better depending on who you talk too, there are definitely different levels of Billet steel. Steve’s crank should not have broke. X3 they stopped the off shore for a reason.


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Old 01-14-2023, 12:07 PM
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The post I made last year regarding my Crower billet crank ordeal....


In the June 2005 issue of High Performance Pontiac magazine Crower had an advertisement for Pontiac crankshafts, advertised as 4340 billet steel. Starting at $1995 plus shipping. My engine builder, a Crower dealer, order one for me. It was a 4.250 Pontiac 3-inch main billet crankshaft for my planned 505 build. Part # 95194C at $1800 and #95320WD for lightweight profiling at $167.86, total $1967.86 plus freight. It arrived that same month and the engine was built and went into service in March 2007.

About 2 years later I had a bearing issue and upon teardown we found the crank was cracked on the #2 main. It was sent to Mile High Crankshafts in Denver for repair. The engine was put back in service in Feb 2009.
But 9 years later I developed a low oil pressure issue. During inspection the crankshaft was found to be bent and when the machine shop went to straighten it, the crank cracked. It was toast, so I ordered a SCAT forged 4.250 crank from Paul Knippen as a replacement.

It was about this time frame I was told a rumor that Kellogg crankshafts made some early crankshafts for Crower that were forged and machined to pass off as billet cranks. When I called Crower to report the issue with my cracked crank I brought up that subject. I was assured that never happened. However when I provided all the necessary order information including their sales and work order numbers I also included it had an approved "Special Net Price Code "B" on the paperwork. With some surprise by the gentleman I was then informed the "B" indicated it was a reject. I asked about that ! He offered no explanation regarding this other than to assure me it had nothing to do with the machining of the crank. At the time I failed to ask if it was made from a USA billet or an import.


.


.

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Old 01-14-2023, 12:12 PM
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I believe that "arma-steel" is a name Pontiac used when they were making their own crankshafts. I don't believe "arma-steel" is actually a type of material.... But I could be completely wrong on that.

Secondly I'm not looking to "praise" the factory Pontiac crankshaft (but maybe we should) but I certainly believe up to a certain power level little will be gained by purchasing a forged crankshaft "just incase". The power levels the good ole 103 survived at in the Grocery Getter will never be reached by 99% of the folks using a forged crankshaft.... JMHO

I also think if the forged Chinese cranks were around back in the day the Grocery Getter guys would choose to use them over a 103 crankshaft, I know I would.

You can talk numbers all you want, but you also need to consider on paper the over the pond cast cranks are much better than a factory 103 crank.... I'd choose to go with the 103 crank nine times out of ten.

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Old 01-14-2023, 12:23 PM
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Quote:
Originally Posted by Steve C. View Post
The post I made last year regarding my Crower billet crank ordeal....


In the June 2005 issue of High Performance Pontiac magazine Crower had an advertisement for Pontiac crankshafts, advertised as 4340 billet steel. Starting at $1995 plus shipping. My engine builder, a Crower dealer, order one for me. It was a 4.250 Pontiac 3-inch main billet crankshaft for my planned 505 build. Part # 95194C at $1800 and #95320WD for lightweight profiling at $167.86, total $1967.86 plus freight. It arrived that same month and the engine was built and went into service in March 2007.

About 2 years later I had a bearing issue and upon teardown we found the crank was cracked on the #2 main. It was sent to Mile High Crankshafts in Denver for repair. The engine was put back in service in Feb 2009.
But 9 years later I developed a low oil pressure issue. During inspection the crankshaft was found to be bent and when the machine shop went to straighten it, the crank cracked. It was toast, so I ordered a SCAT forged 4.250 crank from Paul Knippen as a replacement.

It was about this time frame I was told a rumor that Kellogg crankshafts made some early crankshafts for Crower that were forged and machined to pass off as billet cranks. When I called Crower to report the issue with my cracked crank I brought up that subject. I was assured that never happened. However when I provided all the necessary order information including their sales and work order numbers I also included it had an approved "Special Net Price Code "B" on the paperwork. With some surprise by the gentleman I was then informed the "B" indicated it was a reject. I asked about that ! He offered no explanation regarding this other than to assure me it had nothing to do with the machining of the crank. At the time I failed to ask if it was made from a USA billet or an import.


.


.

Steve the biggest issue with Crower is they never found a competent guy to replace Reid Oliver. Any of the guys that answer the phone over there nowadays is not going to get you good information. Unless the janitor answers the phone, he may accidentally transfer you to one of the engineers.

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Old 01-14-2023, 12:39 PM
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Somewhat related to your comment Paul. My engine builder never delt with Crower sales. He delt with fellows in the back. My contact at the time was Kerry.

Reed Oliver was involved with approval of the billet special net price code I mentioned.


.

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Old 01-14-2023, 12:46 PM
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Quote:
Originally Posted by mgarblik View Post
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.
The reason why I make a big deal about the "Timkin Ball Bearing Steel" cranks, Mike, has to do with HOW CLEAN the STEEL IS before you start the machine work carving the cranks out of the Billet Material.

The "dirt" in the material creates "Voids" in the steel which are potential
locations for the crank to crack and fail. Even if it is a Billet material.

The "Timkin Ball Bearing Steel" billets that Moldex Crankshaft has always used to make billet cranks is a "very clean" steel.

When Bob & Frank and the BOP guys wanted to bring in the chinese cranks for the Pontiac Market,
I said we need to see how clean the steel is vs the Timkin Ball Bearing steel material.

So I had the Ball Bearing material tested. As advertised very, very clean steel.
Maybe one or two specs of dirt in a 2" x 2" section of material.

I had material from the off shore "Scat Cranks" tested. Of the batch of offshore material I had: the steel probably had less than 50 specs of dirt in a 2" x 2" section of forged material. A pleasant surprise.

I checked a couple of other brand steel billet cranks at the time and there was one other crank custom manufacturer (using the same material - "Timkin Ball Bearing Steel") that also had the very clean results.

Now all of that said, if the billet crank failed in a high stress location due to that one spec of dirt, then that is
the luck of the draw. Impossible to get perfectly clean steel. But the odds are like a Russian Roulette with a firearm.
If you have a revolver with 6 bullets in the weapon there is a high probability that you are going to die unless there
is no firing pin to fire the round. So there always are exceptions.

Same deal with quality Moldex or Bryant Crankshafts made with Ball Bearing "Clean Steel".
You may still have a failure but the odds of a failure are much much lower. You get what you pay for.

You may have a crank made with dirty steel that at a given HP level never fails.
You may have a Ball Bearing Steel crank that fails at 3500 hp due to the crank design and specific
engine crank support structure (block) where any crank would fail.

But IF you are buying better material cranks then the "odds" of success are in your favor.
500 mile NASCAR crank sees a lot different stress over time vs a 6 second drag engine.

Tom V.

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Old 01-14-2023, 12:53 PM
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Somewhat related to your comment Paul. My engine builder never delt with Crower sales. He delt with fellows in the back. My contact at the time was Kerry.

Reed Oliver was involved with approval of the billet special net price code I mentioned.


.


Kerry is a smart guy. He was/is the head of the crankshaft department. Reid was the guy that would dig up the answers over there.

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Old 01-14-2023, 01:06 PM
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Jay

Your understanding is sound and I appreciate the descriptions.

My only suggestion is to replace your term "elasticity" with resilience or toughness. Like Elarson shared and you understand, the difference between yield strength and ultimate tensile strength is a measure of ductility. This can indicate "toughness", or ability to absorb overstress without fracturing.

Fatigue resistance will be more about ultimate tensile strength and less about toughness but both are important for a crank. As discussed in this thread, there are MANY ways a crank can fail.

I would expect a forged 4340 crank to outperform a cast crank in every way. Every property follows microstructure, which in turn follows composition, fabrication history, and heat treatment. "Dirty" material will have more inclusions (sulfides are typical). Poorly-processed material will have those inclusions agglomerate and form large chunks instead of being dispersed.

Being a dinosaur metallurgist, I started work for a giant vertically-integrated corporation when US manufacturing was robust, and then "transitioned" to dealing with materials and parts sourced from all over. I expect vintage GM-manufactured cranks to be highly-engineered, high-quality, and consistent parts. I don't buy into any general claims of foreign material being inferior but I do know it costs money for a supplier to both "know" what they want and to make sure they get it. If you want to know what the microstructure looks like, somebody somewhere has to get paid to section the part and look at it. GM did this. Others today... maybe not so much...

Having zero experience with automotive parts, I enjoy and value all the posts in this and any thread that talks to materials and failures. You guys know your stuff!

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Old 01-14-2023, 01:19 PM
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Having had a SD 421 990 crank they where a twisted forging and darn heavy even compared to a 455 crank.

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