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OEM bolts, being torque to yield, are of course for the dirty, unwashed, knuckle-dragging masses...not the alpha cognoscenti that of course populate this site!
hey I represent that knuckle dragging, dirty finger nail remark! I prefer OEM TTY. They are way cheaper (that makes a difference when you have 4 engines like I do) and every bit as effect if done right.

It was really funny watching the YT video a few months back from Nathan’s garage when he couldn’t figure out how to do TTY OE bolts on his S85 so he threw them out and went with BE’s ARP bolts. Some people only know how to use clickers....
He also used random Orings, then talked about how he didn’t skimp or cut corners.
 

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hey I represent that knuckle dragging, dirty finger nail remark! I prefer OEM TTY. They are way cheaper (that makes a difference when you have 4 engines like I do) and every bit as effect if done right.

It was really funny watching the YT video a few months back from Nathan’s garage when he couldn’t figure out how to do TTY OE bolts on his S85 so he threw them out and went with BE’s ARP bolts. Some people only know how to use clickers....
He also used random Orings, then talked about how he didn’t skimp or cut corners.
I’ve been preoccupying myself by reading a ton of posts on the E9X forum about what bearings to use and what bolts. One thing I read was the bore distortion and how the OEM bolts had the highest distortion amounts.

Aside from cost, is anyone aware of this being a reason to stay away from the OEM bolts?


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Distortion is a function of proper joint clamping force (read: torque). It’s pretty easy to eff up TTY fasteners by over torque (usually inadvertently through a combo of bad technique and tools). I spoke about that in the other thread on reccos for torque wrenchs. The best way to know if it’s done right is to measure stretch/elongation but with the S85/65 con rod design you can’t measure the bolt length. I used to spec out assembly line equipment in one of my early roles at a transmission plant. Achieving uniform torque at spec is not trivial.

For bore distortion, the only real way to measure this is on a DMM and layout the part along the whole circumference.

Bore mics are far from ideal to establish eccentricity, mainly because you don’t know the center, you cannot measure radius, only total diameters. Hence DMM.

I wouldn’t worry so much about eccentricity/distortion if you do it right. There’s a lot of distortion when the rod is in operation. Then there are non uniform thermal expansion effects too.
 

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Hmmm, I had simply assumed that I could get my stretch gauge onto both ends of the rod bolts. Is that, in fact, an issue?

Eccentricity in rod bearings is put into place BECAUSE of rod bore distortion (crank distortion/bending as well but that is less of a factor). Well designed rods have under ~20 microns transient distortion in operation (as opposed to distortion due to bearing crush).

Be careful about torquing up rod w/o bearings then drawing distortion conclusions w/a 2 point measurement. What gmt says about needing a CMM to do this work really properly is correct.

Oh, and I hate TTY bolts and I like to b-tch about them.

Some of the geometry on the BMW rod bolts are....interesting as well. Think the S65/85's are ribbed for pleasure and as I recall the S1000RR's were fully threaded or something. Myself and a friend at ARP have scratched our heads and wondered WTF is up with that.
 

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Yep the rod part of the rod is not bored through, it’s a blind hole. But if you go with Carillos they are!!! so just do that if you really want to use your gauge and your wallet is burning a hole through your pocket.

I think it would be interesting to run the FEA on the stock rods to actually see what the math data predicts as far as deformation, strength, etc. I don’t know how to simulate a cracked cap joint though, so it’s beyond me and i have other crap to fix on the cars.

For who ever was concerned, I wouldn’t fret about distortion from OEM bolts, I don’t think that’s what’s causing the bearing failures we see on the either the S65 or S85. More impactful would be to mic the journals and attempt to match shells. I think that’s a bit overkill but that’s what real blueprinting would entail.

Also use ARP’s lube on the OE bolts under the head and on the threads, not KY jelly. One of them big ketchup packets is enough.
 

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I used ACL bearings for my E92 M3 and I used them again for my E60 M5. This debate needs to end now. We really do not have options. BE is always out of stock and they are way overpriced. The ACL bearings and Clevite (Manufacturer of BE bearings) have the exact same design. If you go with mixed ACL shells, that would be the best way to go. I bought my set from ///M Power Motorsports both times I changed my bearings. They actually custom mix the shells and measure for clearances before selling them.

ARP 2000's are the bolts to go with. They don't cost much more than the OEM bolts so why not spend a few extra dollars and get a better bolt. Just my opinion.
 
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