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 NOT have 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.
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.
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).
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.
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
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!
HOLY CRAPOLA...WHAT ARE YOU GUYS TALKING ABOUT? So the crank case/girdle/main/ooga booga can show signs of damage because of the bearings? My limited experience with the S85 aside....this is the first I'm learning about this.
Ahhhh...screw it. If I blow my engine....I'll just buy a new one and tell the new one what a wuss the old one was.
HOLY CRAPOLA...WHAT ARE YOU GUYS TALKING ABOUT? So the crank case/girdle/main/ooga booga can show signs of damage because of the bearings? My limited experience with the S85 aside....this is the first I'm learning about this.
Seems like it. Main bearing failures have been reported on our sister engine the S65 but it hasn't seem to come up with the S85. I believe P-Chi's is due to crank run out though
Its mid October 2021 and after purchasing more parts have come to the conclusion that there are many scenarios that could damage main-line bearings.
1) Of course user neglect/abuse (oil not to temp or low oil level)
2) Non-balanced clutch replacement
3) Damage to engine from hydro-lock, but working. Scored bores put extra stress on main-line bearings and could have potentially knocked crank of of eccentricity.
4) Could be "normal" for S85, but community only focused on the rod bearings. How many engines are bottom serviced vs. pull-out and complete inspection?
5) Accident/Wreck.....lower on my list of probable causes...but? possible....?
Please add to list, hope the count does not go past 10 points....too many variable to chase!
I am no Troy J, but I have now committed to FIVE blocks and rebuilding. It is such a fun engine, and I enjoy learning...it is life.....learning!
Hope to offer a 0.2mm over short-block in mid 2022....100% OEM unless specs otherwise.
Questions: How should I deliver?
1) Full ready and torqued
2) All parts ready for assembly? Buyer completes final assembly with documented parts.
3) Other options.....? Not willing to offer any sort of warranty other than parts and machining meet/exceed OEM before engine put into service.
P-Chi.
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