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My turn to eat humble pie. Memory is a tricksy beast. In my original post I refered to the seal as C19. It is of course C18 or C18/1. C19 being the shim. How or why I did this I have no idea. Apologies for the confusion.OK, rather than putting information on the forum that I believe to be correct as opposed to knowing that I am correct, I made a call to Steve at Maughan and Sons, the clutch seal modification for B + C series Vincent twins is still available, it is possible that when this mod was done by them they might have cleaned the face of the C20 on a lathe to give a smooth surface for the O ring to mate with, this would not have been done to intentionally dimensionally change the length of the C20, but it is possible that in doing so the C20 does in fact become unusable if you want to revert to the C18/1 bonded seal, so in essence Hugo you were correct, in the past I have got round the problem of a too short C20 by having a little material turned off the thickness off the flange, enough to accommodate a decent thickness C19 shim without locking up the clutch centre, alternatively buy a new C20 from Maughan and Son, they are a thing of beauty, almost to good to put a spanner on.
What issue of MPH is this mod described please?Also see page 139 of 'Into the Millennium' to see a picture of the mod I described earlier. Note that this can be done which ever type of main shaft and nut you have and totally does away with any need to seal the outer end of the shaft.
I have been using the C18/3 mod for many years, probably forty by now although it didn't have a number then , being supplied by the late Tony Maughn. It is easy to fit, and does work, no need for that horribly bodge of gasket cement on the splines.So this new seal C18/3 with aluminum spacer to slip on G3 and the oring to go to the outside of the new C18/3 spacer would appear as my out of scale rough drawing?
The theory being that oil would not leak down the C20 threads?
maybe thread sealant?
Looks like a good design. Anyone successfully using C18/3?
This C18/3 seal also allows me to ignore the C3 mod, which I think is a good design as well.
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here it isTry 747 page 12. I'm lifting that information from the book without going back and checking. The mod is simpler than any of the others and can be done with the use of hand tools if machine tools are not available. The first time I did this, which is probably over 60 years ago, I did it by hand using a small grinding stone in a hand drill. This made a 'vee' in the inside of the tube to take the 'O' ring. Nowadays one would use a lathe, milling machine or whatever. Note that the 'O' ring only needs 10 to 15 thou nip to make it completely oil tight.
I don't think that you are correct Gregg, if you are using the standard parts for the B+C clutches, and you do as you suggest you will lock the clutch centre up solid, the only thing that governs the desired operational length of the C20 nut is the metal outer ring of the Dowty seal C18/1, if that seal, or a derivative of that seal, such as Maughan and Sons supply is not used then the C20 nut will tighten onto the C17 bush fitted to the clutch shoe carrier C13 before it bottoms out into the C18/1 seal recess in the C3 clutch shoe carrier , and you will not get anyway near the 10 thou end float that is desirable, perhaps this method works just fine on the later D type set up, but I would not want to comment on that as I have no experience with the D s.The flat face of the C20 nut shown buts nicely up against the flat face of the C3 carrier. I use a small amount of grey Threebond on the inner face of the C20 nut, on final assembly do the nut up by hand, then tighten fully with a socket bar or rattle gun to a good 60 Ft/lB'S until one of the three slots in the mainshaft aligns with a slot in the C20 nut. Never had one leak, never used "O" rings or the modified Dowty seals in there unless it was set up that way to obtain the right distance for some end float, no less than 10 thou........Use a tiny amount of antiseize on the C5/1 clutch shoe drive pins as these can stick. And a very small wipe of oil in the bushes on the plate carrier, wipe away any excess or else it will end up on the shoe linings...........Don't make any of the parts/fits too tight as this will make the clutch stick in action............Good luck.