Background
A few days ago, m3post member "Malloy" gave us all a tip that VAC had custom made bearings from Clevite. Back in
post #2421 of this thread, I got to the bottom of this and discovered that VAC and Clevite had indeed made some custom S65 rod bearings. I purchased a set, had them shipped overnight, Saturday delivery so I could measure them over the weekend.
There was just two problems with what I was trying to do: 1) I had loaned out all of my virgin rod bolts, and 2) I had shipped out and sold my OEM connecting rods. Getting rod bolts on the weekend was tough (real tough when you hear what I mean). I found a full set down in Monterey, California, on the coast, at the beach, only a few miles from Laguna Seca Raceway. It was a very tough ride, all 45 miles of it, sun beating down and beautiful at 85 degrees. I had also arranged to borrow a set of OEM connecting rods over the weekend. These came from a local shop, straight out of the box, OEM remanufactured connecting rods from BMW. It looks like the remanufactured rods were re-honed, and the rod bolt surface was remachined. These rods had bolts in them, and were untorqued when they arrived.
VAC-Clevite bearings
Right before leaving for that difficult ride to the beach, the VAC-Clevite bearings had arrived. I opened them immediately and discovered they were indeed custom made bearings.
VAC had given me preliminary specifications during my phone call the week prior. This is what they said.
Engine guy calls me back a few minutes later and says it's true...they did contract with Clevite to make some custom rod bearings. The new bearings, as he explained, were designed with 0.0005 inch extra clearance. VAC still adds the Calico coating, which he acknowledged takes up the extra 0.0005 inch -- returning the new bearings back to stock clearance.
So the bearings start life with 0.0005 inch extra clearance, have Calico coating added (which reduces by 0.0005 inch), and you end up with factory rod bearing clearance again.
Now it's time to put that to the test. But first, there's one more thing I need to do.
The Calico coated bearings don't mask off the material from the parting lines, so they must be removed before using. Failure to do this could result in improper bearing crush, which also translates to improper clearance and eccentricity. I'm not sure how many people know this, or do this, which is one reason I'm critical of Calico Coatings in the first place.
It's a simple process. I used 800 grit wet-dry sandpaper and swiped the bearings back and fourth 4 to 6 times in each direction.
Removing the material from the parting lines is a simple, easy, but an essential process. Once it's finished, the bearings should look like this:
Preparing to Measure
Preparing to measure always takes some time. With the new rod bolts, I had to pre-stretch them according to BMW specifications. Once stretched, they're ready to measure.
I also wanted to measure the new bearing eccentricity, so I came up with this nice little diagram to help locate the places I wanted to measure.
Next, it's time to calibrate the instruments, then time to measure.
Measuring Eccentricity
Eccentricity | 5 degrees | 19.75 degrees | 45 degrees | 90 degrees |
| | | | |
| | | | |
| 175 degrees | 161.25 degrees | 135 degrees | |
Measuring Virgin 702/703 Bearings for a Baseline
Kawasaki00 recommended that I also measure the virgin 702/703 bearings as a baseline. He appealed to the perfectionist side of me and didn't even need to convince me to do it. I knew it had to be done; and I'm glad I did.
This would be the first time that virgin bearings, virgin rod bolts were placed in virgin rods (remanufactured by BMW) and measured. This baseline was too important to ignore. So I swapped bearings, and re-measured all over again.
Virgin 702/703's | Rod-1 | Rod-2 | Rod-3 | Rod-4 |
| | | | |
| | | | |
| Rod-5 | Rod-6 | Rod-7 | Rod-8 |
The Results
The results were very conclusive. The baseline measurements on virgin 702/703 bearings, using virgin rod bolts, and virgin (remanufactured) connecting rods showed a perfectly consistent 0.00150 inch clearance. This sets a new baseline for 702/703 bearings. The original baseline measurements used a single crankshaft, and gave a nominal clearance specification of 0.00165 inch. At the time, this was a 0.00020 inch clearance increase over the original 088/089 lead/copper bearings. When the 96 crankshaft journals were rolled up into the measurements, the nominal clearance increased to 0.00170 inch. Now with the addition of these new measurements being rolled up, and the fact that all eight of them were indistinguishable the new baseline for 702/703 bearings goes back down to 0.00150 inch clearance, making it virtually indistinguishable from BMW's original 088/089 bearing clearances we've measured.
With the new baseline established, we can now compare the VAC-Calico custom bearings to see the difference. The original VAC salesman said the new bearings would increase 0.00050 inch before the coating and would equal the same BMW clearance after the Calico coating. The measurements show instead of maintaining stock clearance after the coating, the actually increase the stock clearance by exactly 0.00050 inch after the coating.
Here's the table of measurements.
Virgin 702/703's | Rod-1 | Rod-2 | Rod-3 | Rod-4 | Rod-5 | Rod-6 | Rod-7 | Rod-8 | Min | Max | Official | Min Dev. | Max Dev. |
| Rod B.E. Bore | 2.20610 | 2.20600 | 2.20575 | 2.20580 | 2.20580 | 2.20590 | 2.20580 | 2.20570 | | | | | |
| Rod Journal Diameter | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | | | | | |
| 702/703 Bearings | 2.04800 | 2.04795 | 2.04800 | 2.04800 | 2.04805 | 2.04800 | 2.04800 | 2.04800 | | | | | |
| 702/703 Clearance | 0.00150 | 0.00145 | 0.00150 | 0.00150 | 0.00155 | 0.00150 | 0.00150 | 0.00150 | 0.00115 | 0.00200 | 0.00150 | -0.00035 | 0.00050 |
| VAC-Clevite Clearance | 0.00210 | 0.00190 | 0.00190 | 0.00210 | 0.00210 | 0.00190 | 0.00210 | 0.00210 | 0.00190 | 0.00210 | 0.00200 | -0.00010 | 0.00010 |
| VAC-Clevite Bearings | 2.04860 | 2.04840 | 2.04840 | 2.04860 | 2.04860 | 2.04840 | 2.04860 | 2.04860 | | | | | |
| Rod Journal Diameter | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | 2.04650 | | | | | |
| Bearing Thickness Top | 0.07840 | 0.07840 | 0.07840 | 0.07835 | 0.07835 | 0.07835 | 0.07830 | 0.07825 | 0.07825 | 0.07840 | 0.07835 | -0.00010 | 0.00005 |
| Bearing Thickness Bottom | 0.07840 | 0.07840 | 0.07835 | 0.07835 | 0.07835 | 0.07835 | 0.07830 | 0.07825 | | | | | |
Bearing Eccentricity
Bearing eccentricity may also be of interest. The VAC-Clevite bearings use the same bearing eccentricity as the original BMW (Clevite) 088/089 bearings. The graph clearly shows this distinction.
Conclusions:
The new baseline for 702/703 bearings show the clearance is about the same as the original 088/089 BMW bearings. Folks who have been banking on this 0.00020 inch increase for their arguments in the bearing threads will need to adjust to this new reality.
The VAC-Clevite bearings show an extra 0.00050 inch clearance over stock. The new bearings are a Clevite Tri-Metal construction using lead-copper composition. The lead-copper composition is highly advised for Blackstone oil tracking because it allows to track lead as an indirect indication of bearing wear and life.
The new VAC-Clevite bearings seem to be the best option available at the moment. I would personally prefer these over the WPC treated 702/703 bearings. And at this point, I wouldn't even consider using the Calico coated 702/703 bearings.
Page-1 of this thread has been updated to reflect this new information.
Photo journal with additional pictures is available here:
http://rcollins-home.org/photobucket....php?album=235