Primary case interchangability

Hello, my first post...glad to be a member of this group and will fill in my profile soon. I am building a tricked out 69 Fastback...dual front discs, rear (not Mark III) disc, Ceriani Forks, belt drive (a must because the rear hub, a modified Triumph, has no "cush") and many other mods. Would like to add an electric start but don't have several grand to shell out. I do have a Mark III parts bike that I can rob for the primary case and all the e-start stuff. I do not want to change from the original right shift/left ..just add the starter. I already have a pre-Mark III 850 engine available I planned on using but could build another using Mark III crankcases except they are some of the pieces already robbed from my parts bike. Finally my question...does anyone know if it is possible to drill and tap a pre Mark III crankcase with the four bolt attaching arrangement used by the Mark III primary and add a starter. In general...any other reason why it isn't possible? Also....and I am sure this will bring great debate, is just how important is the lubrication issue with the kickstart sprag. One faction say's that it is crucial and the cause of sprag failure. Others, including the Alton folks who unlike CNW, still use a sprag but claim that since it only rotates during starting, the lubrication is not an issue and no problem running belt drive. If adapting a Mark III primary to a pre Mark III engine is not feasible, does anyone have Mark III crankcase available? Hope this makes some sense and thanks for allowing me to be part of the group.

Welcome, I can't answer your MKIII primary question, but would rethink the belt drive = cush hypothesis as I'm pretty sure the belt alone will not suffice.

Think you will need a MK3 crank as well.

As kommando said, you will need a MK3 crankshaft with it's longer output shaft to fit the e-start sprocket and sprag. That means you will also need MK3 crankcases, because the MK3 crankshaft is also wider between the main bearings, and can not be fit to pre-MK3 cases. If you use the MK3 cases, you will also need to use the timing side bits that are unique to the MK3.

Ken

Sounds like an exciting project, I wish you well. At 70 I can still kick start a British twin, but I did purchase a CNW e-start kit for the '73 that I'm building and appreciate its' relative simplicity when compared to the Mk3 e-starting system.

Anyway. I'm thinking that you will need a Mk3 engine, or, possibly some flavor of an 850 to house the longer Mk3 crankshaft, keeping in mind that the inner primary mounting surface on the drive side of a non-Mk3 850 will have 3 threaded holes and may not be, spatially, in the same plane as a Mk3 surface. There are plenty of members that can give you chapter and verse on this exercise; the nits and grits are beyond my knowledge, but my point is still quite germane.

The point being that it will be much less expensive, considerably less frustrating and less time consuming to purchase an e-start kit then to purchase and marry all the parts to adapt a Mk3 e-start. Also, do some searching on this site; the Rube Goldberg inspired Mk3 e-start system is amazingly complex, doesn't inspire a lot of confidence once you have seen all the parts, not real reliable, and has 2 primary failure modes: 1) stops working; you kick, push or walk. 2) stops working and locks up the engine; you walk.

All the best in any event.