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is the crankshaft straight?

is the flange that carries the flywheel square to crankshaft?

It may be normal wear due to design deficiencies of the s85 crankshaft in resisting flexing of crankshaft under S6 torque impulses.
 

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Interesting. We do know that BMW used very tight tolerances in their bearing clearances, however we seldom see the crank mains because the engines are so infrequently disassembled. I have seen some similar accounts on one the M3 boards discussing the S65 where someone had issues with their worn mains. I think I asked about this once here but Troy and Jim are no longer here and they are the ones who have seen the most engines gutted. Unlike rod bearings, BMW did have 3 sizes at the factory to chose from and that is etched on the crank and engraved on the block. You should see what code that represents and also measure the clearance yourself since you have the crank and bearings still.
 

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The S65 sees main failures every now and then. Jim had a theory it was due to the cam chain tensioner design as it's usually the front bearing that fails. The S85 does not have main issues (yet - knock on wood).
 

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E60 M5 and building engines
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Discussion Starter #6
is the crankshaft straight?

is the flange that carries the flywheel square to crankshaft?

It may be normal wear due to design deficiencies of the s85 crankshaft in resisting flexing of crankshaft under S6 torque impulses.
Crank currently being Magnafluxed at machine shop for concern of rod journal two heat witness marks. Should have full review within two days and will post results.

Does signs of corrosion. It is main #6 so out of balance flywheel/clutch assembly could had added extra stress?

Will order matched bearings (full set) and measure b/4 assembly of engine.

Mr. P
 

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Discussion Starter #7
Sorry: Does NOT show signs of corrosion.

Interested in learning more about S6 torque impulses. Any recommended links?
 

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Sorry: Does NOT show signs of corrosion.

Interested in learning more about S6 torque impulses. Any recommended links?
That was just a top of the head thought, from 2 years of McMaster University Engineering prior to switching to Geophysics.

There is a statistical power point presentation via a BMW pdf on line that suggests crank design was validated via statistical finite element analysis

I believe the usual iterative expensive destructive testing was bypassed for what BMW initially perceived to be a one off small volume offering.

The inertial Potential energy at 8000 rpm transferred on crankshaft flange in the form of an impulse during an s6 shift would be a significant load additive to the 383 lbft of torque resisted by crank journal at #6 main location could result in sufficient crank deflection to have crank journal to bearing contact.

All just a hypothesis at this point
 

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Back in 2014 Troy shared a lot of his observations of many s85 engines He was taking apart .
Based on his observations I decided a 6.0 stroker would hold up best on track.

Simply I anticipated the billet crank, and rods, along with forged pistons and steel liners would avoid a lot of issues Troy discovered.
Thus my post in this thread have a strong bias not based on irrefutable facts
 

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Discussion Starter #10
That was just a top of the head thought, from 2 years of McMaster University Engineering prior to switching to Geophysics.

There is a statistical power point presentation via a BMW pdf on line that suggests crank design was validated via statistical finite element analysis

I believe the usual iterative expensive destructive testing was bypassed for what BMW initially perceived to be a one off small volume offering.

The inertial Potential energy at 8000 rpm transferred on crankshaft flange in the form of an impulse during an s6 shift would be a significant load additive to the 383 lbft of torque resisted by crank journal at #6 main location could result in sufficient crank deflection to have crank journal to bearing contact.

All just a hypothesis at this point
Hello ticat928,

I LOVE computers and simulations. While working with Nissan, got to learn a lot about stamping, castings, and continue with injection molding and extrusions. Worked with a great die design team that could simulate metals stress and pull/weak points on a CAD model! This enabled us to offer suggestions to designers on die change that did not affect part fit in vehicle and produce a better part!

Will look for BMW paper on crank!

Thank you,

Mr. P
 

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I could not find it on line any more

will look at my laptop I used in 2015
Or my early post, there was a discussion on it
 

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If it's #1 (front) main, and on upper shell it's nearly certainly due to belt tension/startup wear.

Driveline induced torque would probably be at ~30Hz input, whereas the crank natural frequency is probably on the order of 500Hz. Cranks are nearly certainly made by Alfing and are presumably salt bath nitrocarburized.

It could be corrosion due to someone getting zippy with moly content in oils (either via additive or oil formulation). This will also remove DLC on parts that are coated as such, due to typical attendant sulphur compounds with moly additives.

If there's a BMW paper on the S85 or S65 crank, please point me to it!
 

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Discussion Starter #13
If it's #1 (front) main, and on upper shell it's nearly certainly due to belt tension/startup wear.
Hello desmo01

No belt. Chain. No6 @ flywheel. Lower/girdle. Also small sighs of wear on No5 and less on No4 mains, again on girdle/lower.

Mr. P
 
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