I was going to remove the rear NU209 main bearing on the engine, but needed to make a small adaptor to measure the end float on the crankshaft before I do so. This particular engine has a little bit of movement in the rear crank pin, and I need to find out why it has moved.

Historically the engines have had gradual tweaks over their lifetime, and the rear main bearing support plate which bolts to the crankcase is no exception. The first ones were aluminium, and the later ones were cast iron with a flexible lipped seal, as opposed to a steel piston ring. Oil starvation and inadequate capacity have always been an issue, as the cars were introduced to the ever increasing demands of modern day traffic, and I spotted another tweak today.

The early M6 back plate is on the left and the later M8 is on the right, and can you spot the difference?



The answer is the holes are bigger on the later one, which means more oil can be supplied to the rear bearing. After measuring these it equates to an improvement of 15% over the earlier design.