Saturday 14 November 2020

The Camshaft Drive

The chain drive to the overhead camshaft follows the same principle as that for the single cylinder K7 and AJcette engines and was covered extensively in previous blogs. The main difference is that the V-Twin requires an additional sprocket to drive the camshaft for the 2nd cylinder, resulting in a shaft with one 40 tooth gear driven by the crankshaft and 3 sprockets, one to drive the magneto and 2 for the camshafts,

Blanks were made for the 20 tooth crankshaft pinion and the 40 tooth gear as before and the teeth cut on the milling machine

and then heat treated and, together with 3 sprockets, were keyed onto the shaft.

These are a tight interference fit and although it is highly unlikely that they would ever shake lose, the gear and each of the sprockets were laser welded to their neighbours. The extremely fine fillet welds can be seen in the picture below.

To minimise the width of the assembly the location of the teeth on the middle sprocket is staggered with respect to the sprockets either side to avoid the rivets on the chains interfering.

The outrigger bearing support was made in a similar way to the previous K7 engine and the whole assembly could now be mounted on the timing-side crankcase.

For the first time, it was now possible to try the engine for size in the newly-acquired frame and to put together a crude mock-up of a V-Twin motorcycle. With the addition of brass plates on the end of both camboxes (where the bevel drive on the Velocette usually resides), a dummy spindle to replace the camshaft and a couple of chains the engine could now be placed in the frame to see if the combination would work.

It seemed that it would although space would be very tight in a number of areas – the proximity of the rear cylinder inlet tappet and the front cylinder exhaust tappet and exhaust port to the frame and the small space available for a gearbox.

It was also fairly obvious that the rear cylinder exhaust and front cylinder inlet were in such close proximity that there would be zero chance of this combination working as it would be impossible to fit either an exhaust pipe or a carburettor.

….and, in any case, I didn’t want this bike to be a Vincent lookalike! And so another plan was hatched….

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