Norman,
The crankpins in the Dragonfly crank are drilled for direct oiling - this method is preferred to the side oiling system used on the Mark cranks, but it makes the end float on the bigends more critical. Too much end float allows the majority of the oil to escape from the front (right) bigend, leaving the rear (left) bigend starved. The only mention of bigend endfloat on postwar models is .004" on the T35 crank. I find this is a little tight and does not supply enough oil to prevent pistons nipping up. After some experimenting, I have found that .006" is just about ideal for good oiling without swamping the rings and trailing smoke. On my own Dragonfly I have reverted to a Mark centre web and undrilled crankpins running in needle roller bearings - this crank has now done in excess of 30,000 miles and when last checked, the crank was as good as the day it was fitted.
Regards,
Eddie.
