Modification to Main Bearing Panel

As I have discussed earlier, the MBP in this motor pre-dates a Lotus modification introduced to stop rapid wear of the rear crank thrust washers. The modification consists of using a notched main bearing in position 5 allowing oil to exit the bearing. A chamfer is then formed alongside the bearing allowing the oil to flow on and supply the rear thrust washer.  Early motors such as mine were recommended for upgrade the next time they were stripped. My motor has certainly been substantially rebuilt on at least one occasion yet this modification had not been performed. In later motors the need for this adaptation was removed by using a redesigned MBP. My first concern was that someone might have swapped the MBP for the later type, however enquiry proved this is most unlikely as block and MBP have to be machined closely together. Its not impossible to swap them but the cost would likely be prohibitively high. I was able to confirm that my MBP was original since both block and panel are numbered when machined together. This is the explanation for the number stamped on MBP web observed earlier. The block is in fact stamped with the same number but its hidden away behind the crankcase breather.

Block/MBP number here stamped on the MBP 

And here on the block behind the crankcase breather tube...

who would have known?

This meant that the modification was required so, using a small needle file, I created a chamfer on the right hand side of Main bearing no 5 (rear).

Main Bearing 5- rear of MBP, rear thrust washer slot visible before ...

... and after modification.

The next part is to file a round notch in top right hand edge of the lower shell 0.5 cms from the groove locating peg to allow oil to exit towards the thrust washer via the channel I have just made. It may be possible to buy a pre-notched washer, however I think filing the notch with a round file should be sufficient. Hopefully this will prevent in future, the wear at the rear thrust washer which increases end-float and I suspect is responsible for the greater longitudinal wear to cylinder 4.