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Old 10-24-2008, 09:52 AM   #1
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Exclamation Broken M96 crankshaft- X-51s fail too!

WOW, this is one of the more extreme failures I have ever witnessed from any engine.... Its not too often that a crankshaft shears on the track on an engine that has 7 main bearings, but this one damn sure did!

The engine has the 3.6 X-51 package and was making 325 RWHP and had seen TWELVE THOUSAND track miles prior to this failure. We had initially thought the engine had broken a rod due to the material that came from the oil sump, but as soon as the engine arrived at our facility a 5 minute inspection found the crankshaft to be in two pieces!

The material these cranks are made from is powdered metal, it's what most modern engines use for crankshaft and connecting rod materials and I am less than impressed with it thus far. I can't believe that a component with such mass could break so extremely.

I feel that this failure was attributed to by a couple of things-
1- The engine was "upgraded" to a lightened flywheel. This new flywheel was installed onto the existing stock engine without being balanced to that assembly. This created an imbalance in the rotating mass AND it did away with the factory dual mass flywheel.

2- The dual mass flywheel was removed to alow the single mass lightened unit to be installed. This eliminated ALL MEANS OF HARMONIC DAMPENING!! The crankshaft was forced to absorb ALL harmonics from the engine and transaxle when the dual mass unit was removed..

So- adding the light weight flywheel was a double negative, not only did it create imbalance, it also eliminated the harmonic dampening of the dual mass arrangement.

Due to this I feel that adding a lightweight flywheel to any existing engine is not a wise decision, and that they should only be added when the entire rotating mass can be balanced and indexed to accomodate the lightweight unit. This means engine disassembly, so I'd only add one of these when doing one of our performance upgrades so the entire assembly can be precisely balanced.

This X 51 will be going back together with our 3.8 package applied using LN Nikies cylinders. It will see some head work upgrades along with severe duty valves and Len's spring package. We'll be upgrading the rods from the stock powdered metal units to LN Billet connecting rods and we'll also be applying many oil system mods to this one. Since the crank needed to be replaced, a Flat Six Innovations Billet Chromoly Crankshaft is being used (instead of another crappy Porsche powdered metal unit) and is in the process of being made now. I feel quite certain that these mods and materials will eliminate failures in the future when coupled to our balance and assembly procedures.

Target for this engine is 425HP at the flywheel N/A

Now, here are some pics of the autopsy. Very few eyes have ever seen the anatomy of an X 51 internally-

Last edited by Jake Raby; 10-24-2008 at 10:29 AM.
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Old 10-24-2008, 05:40 PM   #2
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Hey Jake

For the less educated, could you explain how a crankshaft is created from powered metal?
Weren't cranks forged in the old days from a solid billet and then machined?
How would you compare the new technology to the old--durability/price?
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Old 10-24-2008, 05:56 PM   #3
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Ooops how the hell did this happen? The motor should have an electronic babysitter to keep the limiter from allowing it to downshift that probably caused this.

Oh well the electronics will only save so much. It will not save it if you go from 4th to 1st instead of 4th to 3rd.
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Old 10-24-2008, 06:33 PM   #4
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Quote:
Originally Posted by MikenOH
For the less educated, could you explain how a crankshaft is created from powered metal?
Weren't cranks forged in the old days from a solid billet and then machined?
How would you compare the new technology to the old--durability/price?
The newer methods of component manufacturing consider cost more than longevity- just like the rest of the M96 engine- thats why they fail.

Older cranks were true forged units, typically 911, 356 and 914 cranks were 1045 steel forgings made with conventional methods.. A google search on the topic will explain exactly how a crank is forged and it'll be easier to comprehend than anything I could explain in the 10 minutes I have to make this post :-)
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Old 10-24-2008, 06:37 PM   #5
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Quote:
Originally Posted by JP-s-in st. louis
Ooops how the hell did this happen? The motor should have an electronic babysitter to keep the limiter from allowing it to downshift that probably caused this.

Oh well the electronics will only save so much. It will not save it if you go from 4th to 1st instead of 4th to 3rd.
The engine was never over revved.. It had no signs of any over rev in the valve train and the remainder of the engine looked great inside.

The driver just heard a large bang and then a rattle- He thought the engine snapped a rod in half and so did I until my initial inspection before tear down.

I have never seen a crank snap in any engine from an over rev, the first thing that sees over rev damage is valvetrain components.
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Old 10-24-2008, 09:46 PM   #6
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Quote:
Originally Posted by Jake Raby
The engine was never over revved.. It had no signs of any over rev in the valve train and the remainder of the engine looked great inside.

The driver just heard a large bang and then a rattle- He thought the engine snapped a rod in half and so did I until my initial inspection before tear down.

I have never seen a crank snap in any engine from an over rev, the first thing that sees over rev damage is valvetrain components.
+1! The limiting factor in engine revs has always been the reciprocating gear - Valvetrain, Rods/Pistons and ancillaries... never the rotational components!

Pressed Metal technology is 'better' from the standpoint of 'controlling' the mfg. variables and cost... but ALWAYS at the expense of reliability/durability.

Just another example of Porsche's increasing arrogance - spend $50k+ on a car... get a pressed metal crankshaft... beautiful!
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Old 10-25-2008, 04:17 AM   #7
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Its all about the dollar... Maybe one day Porsche will have to pay for these mistakes.
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Old 10-25-2008, 05:30 AM   #8
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Quote:
Originally Posted by Lil bastard
+1! The limiting factor in engine revs has always been the reciprocating gear - Valvetrain, Rods/Pistons and ancillaries... never the rotational components!

Pressed Metal technology is 'better' from the standpoint of 'controlling' the mfg. variables and cost... but ALWAYS at the expense of reliability/durability.

Just another example of Porsche's increasing arrogance - spend $50k+ on a car... get a pressed metal crankshaft... beautiful!
I thought the engine did rather well considering it has an aftermarket flywheel and 12,000 track miles.
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Old 10-25-2008, 06:04 AM   #9
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Quote:
Originally Posted by Jake Raby
The newer methods of component manufacturing consider cost more than longevity- just like the rest of the M96 engine- thats why they fail.

Older cranks were true forged units, typically 911, 356 and 914 cranks were 1045 steel forgings made with conventional methods.. A google search on the topic will explain exactly how a crank is forged and it'll be easier to comprehend than anything I could explain in the 10 minutes I have to make this post :-)

Given the price of these cars, it is pretty sad that Porsche is thinking low cost on something like a CRANKSHAFT!!!!!!!!!!!!!!!!!!!!!!!!

I can see this if I am buying a Yaris or other toss away car.

Man, this is pretty pathetic for a company like Porsche.
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Old 10-25-2008, 09:34 AM   #10
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+1 on the lightweight flywheel issue. Now knowing I have a powdered crank in there I appreciate the flywheel's rotational mass soaking up most of the engine killing harmonics in my street car. If it were an F-1 motor that only had to go three races I might feel differently.
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Old 10-25-2008, 04:40 PM   #11
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Its not just the loss of the mass, but the loss of the dampening of the second mass of the stock unit that is so critical...
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Old 10-26-2008, 11:54 AM   #12
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Just for grins, I looked up the specs on the C5 Z06 motor and they mentioned that the main bearing caps and connecting rods were made out of powered metal. The crank was Cast Nodular Iron with Undercut and Rolled Fillets.

Not to beat this to death but I did a search and couldn't fin much on the technology of making these types of parts from powered metal;briefly, what's the process of turning powered metal into these parts?
thanks for any help.
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Old 10-26-2008, 01:54 PM   #13
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Quote:
Originally Posted by MikenOH
Just for grins, I looked up the specs on the C5 Z06 motor and they mentioned that the main bearing caps and connecting rods were made out of powered metal. The crank was Cast Nodular Iron with Undercut and Rolled Fillets.

Not to beat this to death but I did a search and couldn't fin much on the technology of making these types of parts from powered metal;briefly, what's the process of turning powered metal into these parts?
thanks for any help.
Basically, what happens with powdered metal is that small metal spheres are placed into a mold and heated and pressurized. The little pieces of metal are soft enough from the heat that they stick to each other but they don't technically melt together as their grain strictures are not combined.

It's a good way to make light parts relatively inexpensively. There isn't much wasted material or post machining required. The resulting material is lighter than a forged part, for example, of the same material because it's somewhat porous. It's also not as strong, but that can be overcome with the right design.
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Old 10-26-2008, 04:49 PM   #14
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The connecting rods out of the '08 Corvette are powdered metal with cracked cap - they are one ugly, cheap rod - the beam isn't even symmetrical if you were to cross section the rod. Excellent example of cost cutting to make it just strong enough to scoot by. I've seen a lot of connecting rods come by my desk working with R&R to help develop their billet rods for countless applications and there is a whole lot of room for improvement in many engines.

The problem with the M96 rods is that the bolts are just junk, but because there is no good way to resize them being cracked cap, you can't put better bolts in them. The rods themselves aren't too bad - the bolts and then the crankshaft itself are the weak spots for sure. One of my aircooled customs stated that their shop sees alot of 997 engines with snapped cranks when taken to the track...
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Old 10-26-2008, 09:20 PM   #15
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There are several things to consider when using pressed metal tech to form a part. Pressed metal pieces perform best under compressive force and much less so under tensile force or torque (twisting). This is what surprises me about using this tech for a crank, seems to be one of the least suitable environment.

But, I'm no Porsche engineer, so they must know something I don't. Either that, or the bean counters have veto power over the engineers, which come to think of it, maybe isn't all that much a stretch.

But, with CNCing being all the rage today, it would seem that they could get a cost (and reliability) effective alternative going that route with a forged billet.

Then again, a little perspective may be in order - this is the 1st crank failure that I'm aware of and it occured in an extreme application (racing). Still, it was the X-51 part. I can more easily see the stock crank using pressed metal, but am really astounded to see it adopted for the premium, race purpose part.
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Old 10-27-2008, 04:11 AM   #16
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I am sending the Crankshaft to Stork Laboraories to have a metallurgical study done on it's composition.. This will occur as soon as we get all the dimensions from it necessary to complete the new billet crank.

I feel the crank was not the determining factor, the imbalance it was absorbing surely made a big difference in the mode of failure.

None of this will happen again as I will be balancing and indexing the LWFW as well as the DMFW to two new pressure plates and will introduce noth of these when the engine's rotating mass hits my CN balancer as a new assembly.

Balance is critical, especially at high revs on the track under constant acceleration.
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Old 10-27-2008, 05:34 AM   #17
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Quote:
Originally Posted by Lil bastard
There are several things to consider when using pressed metal tech to form a part. Pressed metal pieces perform best under compressive force and much less so under tensile force or torque (twisting). This is what surprises me about using this tech for a crank, seems to be one of the least suitable environment.

But, I'm no Porsche engineer, so they must know something I don't. Either that, or the bean counters have veto power over the engineers, which come to think of it, maybe isn't all that much a stretch.

But, with CNCing being all the rage today, it would seem that they could get a cost (and reliability) effective alternative going that route with a forged billet.

Then again, a little perspective may be in order - this is the 1st crank failure that I'm aware of and it occured in an extreme application (racing). Still, it was the X-51 part. I can more easily see the stock crank using pressed metal, but am really astounded to see it adopted for the premium, race purpose part.
Cutting billet parts is expensive because of the time and wasted material. Definitely more expensive than powdered metal.
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Old 10-27-2008, 07:09 AM   #18
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The X51 engine is no different on the bottom end. It is a series of top end modifications, heads, cams and intake, porting etc. Bottom end uses the same parts as the regular 3.6.

While the M96 motors have some issues, personally I don't see this failure as one of them. The 964 based motors have seen crank failures at the track with their true drop forged cranks. To me this is an issue of running a street motor on the track at sustained high rpm for over 12k miles without tear down and inspection or balancing of reciprocating masses.

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Old 10-27-2008, 07:19 AM   #19
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Originally Posted by tholyoak
The X51 engine is no different on the bottom end. It is a series of top end modifications, heads, cams and intake, porting etc. Bottom end uses the same parts as the regular 3.6.

While the M96 motors have some issues, personally I don't see this failure as one of them. The 964 based motors have seen crank failures at the track with their true drop forged cranks. To me this is an issue of running a street motor on the track at sustained high rpm for over 12k miles without tear down and inspection or balancing of reciprocating masses.

-Todd
Now we are back to that old debate about whether running these engines hard is GOOD for them.
Based on that theory, the cars that are tracked should be totally flawless??
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Old 10-27-2008, 07:23 AM   #20
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Big difference between lugging these engines along at 2k rpm on the street and using a street engine as a race motor without modification or testing.

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