Thursday 4 June 2020

The Crankshaft

The crankshaft was in a similar condition to the rest of the engine when received.

I have been using Alpha Bearings in Dudley for any crankshaft work for many years and had got to know Max Nightingale very well during that time. Alpha’s work has always been of the highest quality and so, after ordering new bearings, the crankshaft was immediately taken to Alpha’s premises for a complete rebuild – new big end, small end and 2 new mainshafts.

The lubrication system on the K7 (and K10, which has the identical system) was a huge advance on previous AJS engines. In summary, this is a full recirculating system using an AJS-manufactured external reciprocating oil pump that is driven at half engine speed from the end of the camshaft drive shaft and which provides 2 outlets: one to the cambox and the other to the cylinder and bottom-end lubrication. Lubrication to the big-end is provided via a drilling through the drive-side crankcase that connects to a phosphor-bronze oil distributor ring that is sandwiched between the 2 drive-side main bearings. From there, oil enters the drive-side mainshaft via a radial drilling and then to the big-end through further drillings within the crankshaft. Oil is scavenged from the bottom of the crankcase via a gauze suction filter and returned to the oil tank. Overall, this lubrication works well and AJS did not make any significant modifications during the production of these OHC engines.

A new oil distributor ring was made (this is a simple 0.25” thick disc with annuli on the inside and outside diameters and 4 radial drillings connecting the annuli) and the complete crankshaft was ready for re-assembly into the crankcases.

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