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Jake Raby

Snapped Crankshaft (with pics)

28 posts in this topic

WOW, this is one of the more extrememfailures 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 **** 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 ompressed 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 Nickies 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 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 this deeply-

post-34760-1224872113_thumb.jpg

post-34760-1224872122_thumb.jpg

post-34760-1224872136_thumb.jpg

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I'm surprised why Americans put money in a ordinary M 96 street motor, you can see that the distance between the rear crankshaft bearing and the flange, is too large. The acting oscillation by a small imbalance has since the introduction of the engine problems ( one of the RMS causes ) M 96 construction is too weak to be powered. Nobody use this type of engine for track here, they all use GT2 and GT3 based engines, for the more rigid crankcase and shaft. X-51 and a little more will be OK for a reasonable M 96 engine lifetime, but not too much. Just my opinion.

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Its just like pretty much any other engine.. The factory will produce it and a few innovators will make it better, mostly through trial and error..

The component thats replacing this one is entirely over-kill, it won't happen again. It probably would not have occurred anyway if the dual mass flywheel would have remained in place.

Keep in mind that this engine has 12,000 TRACK miles on it, that means it could have ran at Le man 4 complete 24 hour events.

Edited by Jake Raby

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Sorry to hear about your shaft, but your conclusions are at best hypotheses. It is unfortunate, but I doubt the LWFW played as large a role as you FEEL. I'm with RPM...you should start with an Mk. II variant...

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Interesting. This sort of crank failure has been seen a few times on 964 and 993 engines when people removed the main pulley that incorporated a harmonic balancer and replaced it with the RS pulley that did not.

Also the M97 3.8L engine I am working with now shows that Porsche has incorporated a harmonic balancer into the pulley on these motors. That, and having 3 separate AOS on the thing are just a few of the changes over the M96 motor.

post-4060-1224889583_thumb.jpg

Keep up the good work Jake.

-Todd

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Sorry to hear about your shaft, but your conclusions are at best hypotheses. It is unfortunate, but I doubt the LWFW played as large a role as you FEEL. I'm with RPM...you should start with an Mk. II variant...

This wasn't my shaft- It belongs to a really good Client that wants more performance and some better parts to help avoid these problems in the future.

My statements may be hypothetical at this point, but RPM alone doesn't cause this sort of failure. Unlike most individuals I will dig to the bottom of an issue to uncover the true source of the problem. We are doing this with this X 51 just like the other M96 engines we are documenting after they fail. We feel that it is much easier to create real solutions to issues if they are fully understood, and sharing these just might save someone else several thousand dollars.

What I stated isn't just what I FEEL, but I have collected the data to support the claim-

We have a front mounted harmonic damper in testing that should significantly reduce the issues that arise when the dual mass is removed or when some imbalance exists.

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My statements may be hypothetical at this point, but RPM alone doesn't cause this sort of failure. Unlike most individuals I will dig to the bottom of an issue to uncover the true source of the problem. We are doing this with this X 51 just like the other M96 engines we are documenting after they fail. We feel that it is much easier to create real solutions to issues if they are fully understood, and sharing these just might save someone else several thousand dollars.

What I stated isn't just what I FEEL, but I have collected the data to support the claim-

We have a front mounted harmonic damper in testing that should significantly reduce the issues that arise when the dual mass is removed or when some imbalance exists.

Well I'm a statistician and would be happy to look at your data and your sampling plans to determine what you actually have. Again, not trying to challenge your feelings, just don't want to hear pre-mature generalization.

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Crank pin-fillet-web type failures are not uncommon when combined with the number of cycles this engine was exposed. This crank was probably run at near max rpm for its entire life and could easily have failed due to cyclic/fatigue failure.

The cranks are dropped forged in the 996 engine (Ref. PNA 499 921) and the rods are forged as well. I am not sure what your referenct to powdered cranks implies. I would be interested in seeing your comparisons of crank torsional vibrations up to the 8th order with and without the damper in place.

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just don't want to hear pre-mature generalization

Nothing premature here.. This engine has been apart for a good while and I have just now posted the pics and shared a few comments.

The M96 engine article in the "Tech Forum" of the December 08 Excellence Magazine will touch on this subject and feature highlights of our re-design program for the M96. You'll soon see just how serious we have taken this challenge.

Edited by Jake Raby

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Thanks for the post. I'm sorry to hear about your engine. Here is a Porsche statement regarding flywheels in the 997 GT3-

The engine application is designed for the dual-mass flywheel, conversion to the

single-mass flywheel results in the following problems and consequences:

• The single-mass flywheel causes fluctuations and vibration in the lower rpm range, thereby reducing

the smooth-running performance of the engine.

• The crankshaft is subjected to one-sided loading, causing stress peaks that can result in damage to

the crankshaft.

• The one-sided loading of the crankshaft can cause the pulley to come loose, resulting in damage to

the belt drive and engine.

• Any damage relating to conversion or damage that can be attributed to conversion is not covered

under warranty.

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Thanks for the post. I'm sorry to hear about your engine. Here is a Porsche statement regarding flywheels in the 997 GT3-

The engine application is designed for the dual-mass flywheel, conversion to the

single-mass flywheel results in the following problems and consequences:

• The single-mass flywheel causes fluctuations and vibration in the lower rpm range, thereby reducing

the smooth-running performance of the engine.

• The crankshaft is subjected to one-sided loading, causing stress peaks that can result in damage to

the crankshaft.

• The one-sided loading of the crankshaft can cause the pulley to come loose, resulting in damage to

the belt drive and engine.

• Any damage relating to conversion or damage that can be attributed to conversion is not covered

under warranty.

Thanks for the post.. thats an interesting read for sure, where did you come across that? I'd like to archive it.

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I would be amazed if anyone could put forth a reasonable argument suggesting that installing a single-mass flywheel wouldn't significantly add to the sheering forces exerted on the crank. I personally agree with Jake 100%.

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I would be amazed if anyone could put forth a reasonable argument suggesting that installing a single-mass flywheel wouldn't significantly add to the sheering forces exerted on the crank. I personally agree with Jake 100%.

I would agree if the flywheel was totally wrong for the car, some severe damage could occur. So perhaps in the OP's case the wrong flywheel was installed. My point is that the OP should not generalize that all LWFWs are bad and will damage the car based on just his case. Here are some links...FYI:

European Car

Puma Racing

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The fact that some engines have a LWFW stock is irrelevent to this situation. Those stock, FACTORY installed units are balanced to their respective rotating masses and BALANCED as a unit.

My major gripe with adding the LWFW to an existing engine is the fact that it can't be balanced to that engine's rotating mass since the engine is already assembled. I have several hundred hours of run time on my CN balancer and know the impacts that can be expected when adding components to the rotating mass during the balance process, even if that component has been individually balanced prior to it's addition to the mass.

As I reassemble the engine the same LWFW will be used, but I will balance a second (spare) pressure plate to the assembly and I will also balance the stock dual mass flywheel to the assembly. This will give the client the ability to swap flywheels and have no imbalance as each FW and PP will be indexed to each other as well as to the crankshaft. This flexability and forward thought should be applied by anyone who has their engine apart and is considering the LWFW option.

I'd like to know if anyone who has weighed in on this thread has ever spent 5 minutes behind an Engine Balancer?

As soon as the Metallurgy study is completed on the crank I plan on having it welded back together just so I can assemble the entire mass in my balancer, index all the components exactly as they were ran when the failure occurred and then see just how far out of balance the assembly really was. This is being done because we are documenting (and have been) every single M96 engine failure we come across in detail.

I'd like to clarify that I do not feel that all LWFWs are bad, but my major gripe is they are added to a rotating mass that they cannot be indexed to, thus creating imbalance that cannot be measured or corrected for while the engine is assembled. This imbalance is multipliled by the fact that the second mass is not present to absorb any harmonics when the LWFW is added.

Edited by Jake Raby

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I think this one is going to be hard to determine. Not knowing the state of actual end product from the forging process could lead to a lot of speculation. I have to agree if the LWFW was balanced to the unit than there really should be no harmonics weighing in on the fatigue. The Porsche article was written for those who use aftermarket bolt on parts and just assume it's okay. If one is going to use an engine in race trim at the higher rpms, it only makes sense that the bolt on components should be balanced as part of the unit.

It would not surprise me that there was a flaw in the forging process. It all equated to quality control. Hence the reason to verify componets soundness when installing in an engine used for race, or high speed.

Let us know what you find!

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Jack I'm glad to see that there is someone who is looking for alternatives to reman engines from the factory

Thanks for giving us new expectatives

:D :D

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WOW, this is one of the more extrememfailures 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 **** 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 ompressed 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 Nickies 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 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 this deeply-

Forget all that I say Bravo! 12,000 track miles, operating beyond the engines manufactured capacity. That is amazing pure and simple, I have not seen 12kmiles track racing and you don't want to know the failures I've had! This should not come as a surprise, but unless you're gonna break the engine down and inspect it after every race as the pro's do then you couldn't hope to know about it and I would have to say that even with an inspection you would not find it. :D

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I'm about to replace my clutch and probably my flywheel. I'm considering using a LWF but this is the first I've heard of a balance issue. I have some questions. Please excuse my ignorance, I'll try to be concise. (this is for a daily driver thats only driven hard about 1% of the time)

Doesn't the factory balance cranks and flywheels separately so that any pair would be balanced as a unit?

If they balance the whole assembly together then wouldn't replacing the stock factory flywheel with an identical OEM flywheel be just as bad as an aftermarket flywheel? (balance wise not considering any dampening effect)

I see some aftermarket flywheels advertised as checked for "zero-balance". Is that true for OEM replacements?

Does the dual mass flywheel dampen vibration to the point that no balancing is required? Even at the factory?

Edited by Foster

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I'm about to replace my clutch and probably my flywheel. I'm considering using a LWF but this is the first I've heard of a balance issue. I have some questions. Please excuse my ignorance, I'll try to be concise. (this is for a daily driver thats only driven hard about 1% of the time)

Doesn't the factory balance cranks and flywheels separately so that any pair would be balanced as a unit?

If they balance the whole assembly together then wouldn't replacing the stock factory flywheel with an identical OEM flywheel be just as bad as an aftermarket flywheel? (balance wise not considering any dampening effect)

I see some aftermarket flywheels advertised as checked for "zero-balance". Is that true for OEM replacements?

Does the dual mass flywheel dampen vibration to the point that no balancing is required? Even at the factory?

One thing I can tell you is after I had my aftermarket flywheel installed the transmission is noticably louder on acceleration and at idle. On the positive note the car appears to reach the higher RPM's faster.

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