Sunday, 25 September 2011

An account of the DRM 3 cylinder:

The post below is based on the words of Mike Brown who helped with the machining of the DRM:
"I was approached about modifying the crankcases and as you sit on the bike facing forward the right-hand most casing is as per original, the next one left has most of the careful machining which removed the crankcase area leaving the gearbox in tact with a flat face to butt against. The next crankcase part moving left was just a small crank case section generally about 35mm wide and finally the left-hand most casing contained a full crankcase but with the gearbox part all removed. The whole thing had to be lined up and holes bored for hollow dowels and long studs or with my engine, long specially made cap screws which held the crankcases together. Finally the mouths of the crankcase assembly were skimmed by removing about 0.2mm.”
“Davy had worked out that if we use 2 crankshaft centre sections of existing AS3 parts, we could seal the crankcases and due to the 6 splines that join the cranks together we would only require 2 crank halves to be modified. These were clocked up and the crank pin hole and the counter bore reinstated 120 degree round to the right with the original crankpin hole filled with a plug so as to help restore rotational balance. Once I had finished with the crank parts my good friend and colleague Hugh Ward reassembled the big end and rod assemblies by pressing them together and clocking them up true.”

“DRM racing sponsored a well experienced and able Scottish racer Mr Bill Milne and Bill had used an overbored /modified TA 125 in the 200cc class I think from memory it was 132cc all this work was done with Davy’s close links with Fahron engineering who produced very successful sets of water cooled barrels at that time. Fahron also produced the 3 cylinder barrels by making the cylinder pitch the same as the twin and machining the barrels and liners as they normally would.”
“Many other issues had to be addressed and Hugh would be able to provide this information but I do recall that initially ignition was with a Femsa unit. This machine was a very free revving unit but for various reasons it seemed to lack low down power in my view, probably due to porting, so performance was concentrated at the top end of the power range approaching 14,000rpm and the rider Kaj did run big end assemblies.”

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