Broken M96 crankshaft- X-51s fail too!

[blue2000s]

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.

[cnavarro]

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...

[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.

[blue2000s]

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.

[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

[Brucelee]

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??

[tholyoak]

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.

-Todd