[Malek@MRF]

Originally Posted by Hujan

Malek's point is not so much that VAC bearings are the solution, but that the OEM rod bolts might be the problem, at least insofar as they have a propensity to be over-torqued. So if the car that chewed through the VAC bearings used BMW spec torque-to-yield bolts, this would actually support, rather than contradict, Malek's observation.



Again, the question is not so much whether Harrop is using VAC bearings, but whether they are using VAC bearings and correct torque settings on the bolts. If so, this would again support Malek's theory that the bolts, not the bearings, are the difference maker.

You read my post correctly. I am not saying or implying that the VAC bearings are the solution, nor am I saying/implying any coated or treated bearing is the solution to this very well known and documented matter. My point being here, is that through my many years of engine building and assembly, an improperly assembled engine can suffer from catastrophic failure. Whether the assembly "fault" is a result of what the BMW engineers specified to be the correct choice of fastener or the torque values specific for that particular fastener or a direct result of equipment calibration, this I cannot give a definitive answer to.

In this particular engine, where the connecting rod bolts (ARP) were assembled and torqued exactly to ARP's specification using their assembly lubricant, a certified and calibrated torque wrench (non click type) shows us all something very important: this very engine, with factory connecting rod bearings and bolts exhibited very accelerated bearing wear on the top and bottom of the shells.

Now in this particular situation as well, I am not saying/implying that the factory bolts are over torqued, they can very well be under torqued or they simply can't retain ideal torque and cause an issue.

Per CLEVITE, an over-torqued bearing cap will result in excessive crush, which will create accelerated wear at the bearing parting line, not at the top and bottom of the shells. Also per CLEVITE, and under-torqued or fastener that is not holding correct torque would result in insufficient bearing crush and create uneven wear at the top and bottom of the bearing shells, which is what we see here. Not enough crush can also lead to a bearing not being tightly held within the rod housing and free to move around in the housing. This also hurts heat transfer in regards to the bearing surface. Overheating will kill a bearing.

Originally Posted by JEllis

The critical piece of statistic here is that prior to the VAC Bearings (with tighter expected clearance) the bearings were being chewed up, or at the very least, wearing prematurely. After the switch to bearings with a tighter clearance one would expect to find even more wear but yet we see no wear at all. So what gives? One possible explanation is over torqued bolts from the factory.

What is particularly significant is the difference in bearing wear between the two sets of bearings. If the bearings had shown no wear previously, one could theorize that this was a fluke motor with adequate bearing clearance ect... But due to the fact we have data from the first bearing removal, we know that this car had insufficient bearing clearance initially but sufficient clearance after installing VAC bearings even though the VAC bearings should, by every measurement, decrease bearing clearance.

I agree. The standard bearings in the engine prior to VAC/ARP being installed at 6000 miles showed very poor wear characteristics in the bottom and top of the shells whereas the new hardware and bearings with technically less clearance, though assembled properly, show almost zero wear after 33,500 miles of supercharged use with multiple track days and air-strip events.

Originally Posted by rantarM3

This is getting really interesting. If the bolts were too tight it would mean that the big end of the rod was being deformed so as to pinch the crank journals, right? So would you not then have wear symptoms on opposing sides of the bearings?

See above.

Per CLEVITE, and over-torqued connected rod bolt would yield in excessive crush creating accelerated wear at the parting lines of the bearings and under-torqued fasteners or fasteners that lose their torque due to excessive fastener stretch will yield wear at the bottom and top of the bearing shells which is evident here and almost all S65B40's with bearing wear.

Originally Posted by Groundpilot

OP, interesting info, but you said your client asked you to take this engine apart?
I assume he didnt ask you to do it to make this report. What was the reason?

I purchased this engine from a client, he has a new engine in his vehicle now. He knows about this report, post and engine tear down.