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99 dominator engine/gearbox width


Can anybody shed any light on this situation i have found on putting together a 99 dominator. The gearbox seems to have a lug wider than the engine and the other side of the gearbox.

They all measure 3 5/16" except the bottom of the gearbox which measures 3 7/16". So consequently wont fit between the engine plates.




Andy, I can't read the gearbox number very clearly from your pic, but it looks like it starts with G?? Surely a Dommie box # is prefixed either N or NA for the later ones?



Well thats an odd looking number to me Andy. I've a couple of (very old) Matchless boxes, they have an M prefix unsurprisingly, but still have equal width top and bottom lugs. Also the top diameter of the fixing bolt is much smaller than my Nortons.

I take it the machine was dismantled when you obtained it, so I can only guess it's a very odd box and not Norton. Just put in with the bits by whoever sold you the bike and probably bought in error by them. Any chance you can get back to the vendor for any more information?

Can you put up a few more photos, somebody else might be able to identify.



Well it's clearly a Norton! Looking at Roy Bacon's excellent Twins books, looks very much like the 1953 Model 7 with swing-arm but pre-f/bed frame.

You do not say what year/model/frame Dommie you are working on?


Andy, you have a 'laydown' type gearbox from a single and intended for the plunger or early type swinging arm frame, I believe the shell for the featherbed frame  would have a GB8 prefix and the Model 7 G101. As well as the different mounting lugs the kickstart and mainshaft are also different so even if you modify the lugs you might struggle to line up both the chains. I would look for another gearbox.


Your gearboxes are correct for plunger frames where the upper mount is shorter than the bottom. In general G101.xxxx were for singles and G102.xxxx were Model 7 boxes although this became somewhat mixed in the mid 1950's. For an 88 or 99 laydown box look for a GB8.xxxx stamped box. This box has the same dimensions for top and bottom mounts as the box fits between the engine plates.

Thanks to all for the info.

I've machined off the lower lugs, inline with the upper lugs and square to the mainshaft. .095" off one side and .080" off the other. This makes it the same width as well now as the upper lugs and my engine crankcase engine plate mounts.

It seems to fit ok now, does anyone think it will work?


You need to do a trial assembly with the engine bottom end, gearbox, and rear wheel. Fit the sprockets and clutch and see what lines up and what doesn't, the engine sprocket is on a taper so start there, remember that you will need to fit your chaincase, and it can be awful close to begin with, the rear hub can be moved a little if needed and then the rim tweaked to get the wheels back in line, this is what people did in the Sixties when there was a mania for building hybrid bikes.

If I were going to do this, I would have assembled the engine into the plates and put the assembly in the frame with the back wheel, then assembled the gearbox sprocket and clutch onto the gearbox, then measured everything, then, using the engine sprocket as my datum, I would have worked out where the gearbox needed to sit, then worked out how much needed taking off, and possibly adding to, the gearbox lugs, then worked out where that would leave the gearbox sprocket in relation to the rear wheel sprocket, before I started cutting metal, but you are committed now, so good luck!


From various discussions on the forum, the concensus is that the mainshafts are different lengths for singles and twins, with the twins shaft being the longer one. As was mentioned earlier, G101 suggests that you have a 'singles' box. Search for mainshaft length for more info.

However, as Neil says, with case machining done, only you will know how things will line up.



As it's essentially the wrong box for a 1959 bike/frame you might have been better off looking for an AMC Norton box - fitted from 1957 onwards according to the N.O.C. History pages.  Then sell this Burman box.

Possibly too late now that you've altered it!


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