Hi Roger,
I am of the opinion that oil delivery is not the problem with 'Plus' cranks - the main problem is where it goes once it has reached the crank. Back in the late 20's when Douglas produced the Dirt Track models, they recognised that the oil needed to reach the centre of the crank before it was divided to supply the 2 big ends. They continued with this oil circuitry up to the advent of the 'Plus' machines - even the generator engines and the Mark series cranks fed the oil to the centre web before splitting it between the 2 big ends which were fed from one side (not ideal!). On 'Plus' and Dragonfly engines, the crankpins were larger in diameter and drilled for direct oiling - this provided better oiling to the front big end but tended to starve the rear big end if there was too much endfloat on the front conrod, thus allowing the majority of the oil to be flung out of the front big end under centrifugal force. Eddy Withers recognised this problem and produced a more complicated oiling diagram that split the oil in the centre web but still fed it through holes in the crankpins (I'll see if I can find the Eddy Withers drawing).
Those riders who raced the Pluses in the 50's found that in the longer races (TT, etc.) the engines seldom lasted till the end of the race, and it was often down to big end failure or piston seizures.
In the case of the Dragonfly cranks, I have rebuilt about 30 cranks using INA needle roller bearings, and haven't heard of anyone suffering further problems. In the case of my own Dragonfly, I reverted to the older Mark type oiling (side feed and oil split in the centre web) - my crank has now done about 30,000 miles and at the last check, was as good as the day I first fitted it.
With regard to higher output pumps - George Easton told me that when he was developing his 500cc Mark based racer, he fitted a 'Plus' oil pump but had to revert to an ordinary Mark pump as the engine was overoiling and the rings couldn't cope!
Hope some of this helps,
Regards,
Eddie.
