Yes, think so... the spiral grooves create a difference in pressure, just like a screwpump/augerpomp....the centrifigal force a suction, oil will circulate and refresh the bushes....

I can imagine the viscosity of the oil is also of great influence here... if there turns out to be a special 'WD-mainshaft" the groove might be suited to the oil used by the War Department ??

That could explain the postwar change back to the early version...

But just throwing out idea's, no expert at all and overthinking could indeed be the case :relaxed:

Not sure Ron but just my analysis. There are 3 holes in the 3rd gear on the mainshaft also, one hole can be seen in the top picture. When they act as an exit probably some oil will be drawn into the bush along the mainshaft also...

Think they tried to get some circulation going with all the grooves and holes..... when you look at the kickstart end of the layshaft, the spiral forces some oil into the blind layshaftbush, the surplus oil can flow back through the long hole in the center of the shaft and exits in the heart of the 1st and 2nd gear bushes.

I've checked out some parts lists and as is often the case the result still does not definitively answer the question...

The 1940 WD list and the 1940 'combined' WD and Civilian parts list shows the gearbox main shaft part number as 15-4260...

The WD lists for contract number S1048 (09-1942 to 11-1943)and S7218 (08-1944-1946) shows the number 66-3283...I don't have the list that covers the contract before S1048...

However, the post war parts list for side valve models (1949-55) and the parts list for OHV models (1949-52) both show the 'earlier' number 15-4260...

So, possibilities are...Both post war lists have an error showing the earlier number...Not all that likely I'd have thought...
The post war boxes reverted to the early pattern shaft...That seems illogical at first sight but maybe there was no gain in bush life from the modification that was made but the later shaft was more complicated/more costly to manufacture...Possible...In that case a reversion to the earlier pattern would be advantageous...Any other views on the subject..?...Ian

email (option): ian@wright52.plus.com

The RAF illustrated parts list quotes the 66-3283 shaft and the illustration seems to show the left hand shaft in Michiel's original post. Ron

email (option): ronpier@talk21.com