Belt drive for Dommi 99

Hi Don,

I replaced my original (= chain) primary drive with the RGM belt drive kit for Dominators (which looks absolutely the same as the one sold by Norvil) some 1500 miles ago

It works really well, more smoothly than a chain drive, it's quieter and lighterand no more oil leaks from the primary chaincase!

But you need to know the following:

- The primary ratio is a bit higher than with the chain (because of the pulleys being of different sizes vs sprockets one), but not that much. Up to you to compensate by one tooth less on the gearbox sprocket (or one more at rear wheel). To me, not needed.

- The diaphgram clutch spring gives a "touch" and feeling you need to be accustomed too, but once used to, it's OK.

- Installing the kit is not so easy: I had problems with the alternator stator studs (because my stator is an old one from 1960), with the offset of the rear pulley (too close to the inner primary chaincase), and with the outer primary chaincase (not able to accept the offset of the alternator). All needed adjustments, spacers, calls to Friendly Roger of RGM etc....

The stator base needed also to be filed a bit to accomodate the belt width.

But all in all I do not regret at all having switched to a belt drive, and Roger was really helpful in sorting out those details.

Hope it heps!

Laurent

Previously wrote:

Hi Lauret,

Thanks for your reply.

A friend who had a Belt drive on a Manx commented that heat may be a problem? As the climate here is fairly hot I may have to arrange some cooling....

I also have the original alternator so I may have similar problem to yours.

Don

Hi Don,

That's true that most of the beltcases have some ventilation holes or slots etc... Mine has not and I got no problem this summer which was pretty hot in France (up to 35?-40? C. Maybe still cool compared to Australia!).

The impact of heat may be a dilatation of the belt, which seems flexible enough to accept it. I used mine with far too much of slack (4-5 cm instead of 2 cm) and it created no problem, although it's smoother with the proper slack.

Re: the alternator, it may be worth considering the cost of a post 1960 stator, because adapting the original outer chaincase is quite a lot of work (cutting + welding + painting).

By the way, Bob Newby's belt kit seems to be the best. More expensive but less adjusting work apparently

Hi Don, Below is a copy of my response to a similar question asked by another Norton owner some time ago. Please ignore the parts that have already been answered by replies fromother contributors to this thread.

If you get a bit of spare time, then do lookat some of the belt drive articles in the Technical section of the NOC website. There are several that deal with the benefits and drawbacks of fitting sucha conversion.

In recent years I haveconvertedthree of myNortons to belt drive. Two Atlas's and a 650SS.

The bonus points, each time, were amuch smoother transmission, no oil leaks from the chaincase itself and a very light and easy clutch action. The other plus points were that when pulling off the chaincase cover,to check out the alternator, there was no oil to drain or drip on the garage floor, the belt never needed adjusting for tension and and showed no signs of serious wear after 5 years of hard use. Also, you can get pulleys of differing sizes to help adjust the gearing to suit your bike.

The possibles drawbacks:-

My first conversion kit was clearly geared to suit the smaller engined Dommies as, when first fitted to my Atlas,the engineran at 5000rpm for a 70mph cruising speed. Much too high for an Atlas. So this kit was donated to my 650SS which already had a 20t gearboxand 42t rear wheel sprockets to raise its gearing.

My next kit was ordered with a bigger engine pulley, 34t instead of 32t. This gave a primary drive ratio of exactly 2 to 1 and resulted in 4,400 revs for a 70mph cruse speed. Almost spot on.

Thiskit also came with a 1000mm long belt, which was too long and resulted in the gearbox having to be set as far back as the adjuster slots allowed. This, in turn, made the clutch rub against the outer primary case and also messed up the rear chain length.

Fortunately, you can now get belts of 980mm length which are about the right size to keep the clutch in the centre of the primary cover bulge. Also very useful is a spacer kit which pushes the primary cover about 6mm away from the inner. This stops the clutch centre nut cover from touching the outer when the clutch lever is pulled fully in. (When using a Commando clutch basket)

Thisfirst belt drive kit all came with longer alternator stator studs and spacers to push the stator outboard from the 30mm wide belt. There were two problems here. The studs supplied were too thin and allowed the stator to move sideways enough for it to touch the rotor. Secondly, when in place, the outer case also originallytouched the statorand pushed it against the rotor.I lost two expensive alternators before twigging a fix to cure both problems. The spacer kitmentioned above and some purpose made shouldered studs. Some belt drive kits now can be purchased with 25mm wide belts which also helps to sort out this difficulty.

I found out the hard way that someother very important points need to be considered. Especially when converting an Atlas to a primarybelt drive.

1) Your gearbox bearings must be in 'as new' condition. Any wear in the large main bearing or output drive sleeve gear will allow the gearbox mainshaft drive end to be pulled forward on accelerating hard and back when decelerating and using the rear brake. The change in angle of this shaft then causes the belt to track out and in on its respective pulleys and subsequently grind away on the alternator housing and primary outer cover.

2) You will need some way to hold the top gearbox mounting bolt in a fixed position once the belt tension is set. This could be by fitting an adjuster each side or some other means.

3) With the largerengine pulley fitted I found that the belt used to catch the top and bottom edges of the alternator housing. Some careful filing and buffing sorted this out.

4)If you are going to do some serious riding then you need to consider a means of keeping the pulleys and belt cool. You will be amazed at how much the pulleys expand when they get very hot, such as on long rides. The belts can then become over-tensioned and start to shed teeth. The spacer kit for the primary cover helps here as it allows air to flow past the seal.

There are plenty of belt drive conversion kits, for Nortons,on the market and most are now easy to fit and will do a good job. They usually come as a complete set, including everything to get you moving, or as a basic kit where you may have to supply some bits from your old set-up eg clutch plates. As a general rule the more you pay, the better the set-up. But............ be aware of the drawbacks mentioned and don't sell or give away your original primary gear. You might need it again, one day!!!