Have you thought about trying David Woods who operates as Chronometrics, advertises in MPH and is a VOC member. He knows everything there is to know about these.
I would recommend you think about trying him for a fully reconditioned unit.
If it is the head gearbox then I understand that there were two types, early and late so you'll need to identify to David which one you have.
As relating to the drive in the front wheel, I have seen loads of what I thought to be the same thing at autojumbles only to then find small differences, different spacings, different drive shaft finishes etc. so maybe the answer would be either have a part number (can't see one on mine) or take a Vincent one with you when you go looking.
The front wheel speedo drive, I stripped mine, cleaned and overhauled it myself and put it back together again it worked fine.
The head end, I've had stripped gears and David sorted those out for me for about £35.
There are articles in Forty Years On which describe how they work, how (within limits) to fix them, and from Ted Davis on what speedos were fitted to what bikes. The right angle gearbox on the back, outside the case, is apparently the same as the one fitted to Landrovers.
Don't think so Tom. The ones fitted to Land Rovers will fit and will work and, if I remember correctly Colin Jenner at Conways used to, and perhaps still does, supply them as replacements. However, they are noticably larger than the original items. I have had the Land Rover item on my bike for years but they will not suit the purist.
I had never noticed, but you're right. The right angle box I used on a Smiths conical tacho must be a Landrover one, with a "barrel" about 3/4" diameter, whereas the Vin one is about 5/8". Too late now: I used to be pure as the driven snow, but I guess I drifted... (Mae West).
Beware. The early 5" head gearbox (monkey metal) will break the cable if the bike is wheeled backwards more than a few yards. It is a design fault. The scroll is driven upwards by the pinion until it jambs against the casing.
I don't think it's a design fault Hugo, the effect you describe is caused by the gears wearing thin and jamming when the bike is wheeled backwards.I understand that David Woods can supply refurbished units, but for any DIYers out there, see my article in MPH 669 Oct 04 describing how to replace the gears with new ones from HPC Gears Ltd.
The breaking of cables on early units was well known at the factory and is mentioned in Richardsons book the design was changed to avoid the problem. Incidently another piece of usless in formation if you find the that the teeth on the ring gear on the hub are worn take it off and reverse it and put it back. Teeth on the gear only wear on one side.
I bow to your greater knowlege Paul. This is over 20 years ago but as I remember it the scroll gear (This is probably the wrong technical term but you know what I mean) is champhered at the end in the direction of the thrust when the bike is in forward motion. The other end is not champhered so that when the thrust is in the reverse direction as when wheeling the bike backwards the sharp edges of the teeth dig into the end cap and lock it up solid. At least this is what happened to mine. My garage is at the end of a very steep drive entailing paddling the bike backwards for some distance. The cable would break after the exact same number of wheel turns. It took me a long time and many cables to work it out. I had a slight champher ground on the other end of the scroll and no further problems.
Having just read Paul Ennis' article in MPH 669, I jalouse that the reason for the "Landrover" gearbox being bigger, and therefore "impure", is that it holds nylon gears, not steel, and they have to be bigger. I know that some right angle boxes do contain nylon gears, because I've had them strip, on other (lesser...) bikes. In turn, that suggests is that what one needs to be looking for is a treasure trove of pre-1954 Landrover speedo spares, c/w right-angle boxes with steel gears. At 1954 prices........
I know that the 5" speedo was made by Smith exclusively for Vincent (PEI says so) but am guessing that the gearbox was an off-the-shelf item.