750 cafÃ? racer project

The N15CS into a Featherbed frame will be a struggle, as the N15CS drive side crankcase has only three holes. The N15CS crankcase uses the AMC alloy primary chaincase and also a spacer to fit it into the modified G12CS frame. The Atlas engine in the Featherbed has six holes, for the primary chaincase and to mount the alternator housing onto. The N15CS alternator is hosed in the outer cover of the alloy primary chaincase. The motors look the same, but the Featherbed and G12CS framed Atlasengines do differ in many minor ways. If you can get to look at any G15 or N15up close and personal then the way the primary chaincase is fitted will become obvious.

I had a pair of AMC hybrid cases on my atlas, but because I was young and spendthrift I fitted a belt drive with a sort of Manxish open belt guard, which is OK but needs a sympathetic MOT tester and a close eye on things getting stuck in the belt. If I was doing the job properly I would assemble the empty crankcase and gearbox with its mainshaft and sprocket in the engine plates with the inner chain case half, the sliding seal and gasket, tensioner, sprockets and chain. Adjust the chain tension as if it was on the bike, make sure the rear sliding seal is central around the mainshaft and the holes in the gasket at the front line up with the holes in the inner chain case. You will need to make up dummy spacer and screw to tighten down on the spacer between the engine plates and the inner chain case. (This is the one with the two pegs that fit in corresponding holes in the drive side engine plate) Normally the outer chaincase nut and footrest do this but you can't do the next step with the chaincase in place. Make up a transfer punch of the correct size and dot through the screw holes in the inner case. Disassemble, and drill to tapping size. It's probably best to take this to a local machine shop and have them do this under a large drill or a milling machine as the holes need to be dead on and at right angles to the mating face on the crankcases. The inner cases tend to be a bit bent, usually because of people heaving on the outer chain case /footrest nut in the hope of stopping the leaks, so it 's as well to check with a straight edge before you start, and apply corrective measures if needed. Hope this helps.