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Assembling a Commando Clutch in a Dommi

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I have a 1959 Dommi 99 to which a belt drive modification has been made. This involves a Commando clutch assembly. With the correct tool I sucessfully dismantled the clutch, but now I have to put it together again. I am struggling to refit the large circlip that secures the sprung diaphragm. Are there any special tools available or is there a technique that I am yet to discover ? 

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Bike is 1959 Dommi 99. It has a belt drive fitted. I have had to fit a new alternator (Stator & Rotor). I have fitted these in exactly the same way as the old ones were fitted using the specially designed spacer and spacer cage.However, this seems to protrude so far that it interferes with the chaincase cover when fitted.

Looking at the old Stator I see that someone has ground away some of the encapusalation material all round the circumference. In addition, they have ground a goove in the metal part of the Stator in order to provide space for the two wires to be routed out through the back of the chaincase. Looking at the damage to the wires on the old Stator, this mod doesn't appear to have provided adequate clearance.

So is there a real issue here ? How do I get the  original chaincase cover to fit over a modifed primary drive unit using a belt and a commando clutch ? I'm sure this has been resolved by others, and probably in a way that doesn't involve butchering a new Stator !

 

I am doing this right now with the same problem.

I got a belt drive clutch drum in a kit  from Tony Hayward, but he advised me to machine 5mm off the steel engine pulley and use a 25mm belt to fit a Dommie.

I had to buy a thin outer clutch compression plate (they come in 2 very different thicknesses) to replace the thick one that came with the S/H Commando clutch which I bought ages ago.

If the circlip squashes the plates when you insert it, then no way the clutch can release.

Mine was close with surflex plates, but the circlip still squashed the plates up. I sanded the oil impregnated skin off them with rough sandpaper to take off 0.025" over 8 surfaces.

The plates have to be able to rattle around with the spring compressed using the compressor. You might have to switch to sintered bronze or omit one. A 99 isn't going to produce the torque of a Commando anyway. If the circlip isn't easy to fit, something is wrong. 

I have an Electrex generator/CDI ignition.

The good news is - clutch feels great when you have done it!

A couple of gotchas

1) The release lever that bears on the 1/2" ball in the gearbox to push the pushrod is a different profile for diaphragm springs.

2) Gearbox oil can get down the middle of the mainshaft you can get a gizmo eBay 323516969490

3) the mainshaft disappears into the rotor as it is pushed outward by the belt pulley being fatter than a sprocket - I bought a Command sleeve-nut type nut and retapped it to 20TPI Whitworth Form (they are 20 TPI UNF form as standard)

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I could re-tap a sleeve nut for you for nowt! Just done it for my 99 Deluxe owning mate in Queensland.

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Mike is correct in his reply, I fitted a belt drive for a commando which i got from RGM. This was a decade ago. Other than longer stator studs supplied I was on my own. You will need the commando lever in the gearbox as it is a different profile to the Dommie. I had many issues fitting the belt drive including the studs which were supplied didn't space the stator far enough out from the pulley ( what is this yellow powder inside the case, remove stator to find a neat depression ground into the back of the stator by the front pulley).

I overcame the outer cover problem by fitting a rubber spacer onto the inner case where the foot peg mounts ( I think this was a tank mount of a Commando ). This moved the outer so as the stator didn't foul the outer case but allowed enough threads for that large nut to be done up and the foot peg to be fitted. What you have then is about 15-20 mm of the big rubber sealing gasket showing, a small price to pay for a better clutch and a dry garage floor. I attach an article that I wrote but never submitted to RH. This might help you set up the belt tension and alignment. All this is from memory as I have never had to look inside the primary in over ten years. I did fit an air scoop onto the back of the inner primary to cool the clutch, it does get hot over here in Australia.

 

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Hi Andrew, good to hear a long term success story. 

I needed a spacer between the steel belt pulley and the Electrex rotor, so I used a Commando rotor spacer part-no:  06.0402 turned down to the minimum thickness to achieve that. The Hayward steel engine pulley has a detachable flange, leaving it effectively dished.

I bought the three stator spacers from RGM PART NO: 050064, but they were too long in my case, and they needed the hex section shortening. I was fighting for millimetres, mostly to get enough turns on the mainshaft sleeve nut as well as wanting to avoid having to pack the chaincase.

I wanted to get 80 ft/lb on that standard Commando mainshaft nut. It was very Norton to change to a triplex sprocket, but not lengthen the mainshaft, and just use a deeper sleeve nut for the Commando. But annoyingly they still changed the thread!

BTW whereabout in Oz are you, Bob could use some inspiration?

Hi Bob moved from Melbourne to Surfers about 20 years ago.

He had a wideline 99 when we were both working in Zambia 76-78. We both loved it. He bought a Deluxe and me a 99SS in England in 1978.

His belt drive upgrade has been a long time in the making, but we have a bucket list task to ride round Aus on Nortons.  He bought a Dommie kit which include a coil spring type clutch, but he can't make it fit. My rebuild has been decades too.

One gotcha - you can't adjust the left hand gearbox adjuster with the inner chaincase in place.

I have high hopes of the Electrex genny/cdi! Me and Lucas distributors are not friends any more.

I will pass your contact details on.

Steve

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I made up my own drive side adjuster and have no difficulty in using it. I have a small ring spanner that I have ground the end away . This fits over the threaded rod and onto the adjusting nut and locking nut. I can send you a rough drawing and description. I was just too tight to spend more money to get a manufactured item.

Tell Bob to keep going and not give up.

I would be interested to see how you did that.

I can only just catch a glimpse of my LH adjuster with the inner chaincase it place.

I aligned mine without the inner chaincase, running it with the kick start to check alignment, hoping I can fine tune it with the RH adjuster only post completion.

BTW what did you do about the disappearing mainshaft problem? Do RGM send a super-deep sleeve nut?

I bought one of the seals for the end of the gearbox mainshaft. However I made up a Commando pushrod which is 1/8" longer out of 1/4" silver steel. Then I noticed that the old one was 6mm dia. I wonder if a 1/4" well greased pushrod would stop the migration of oil from the gearbox by itself without fancy seals..

I have a Tony Hayward 10mm tooth clutch basket as sold through RGM. My buildup is basket, surflex, steel, surflex, steel, surflex, steel, surflex, steel - pressure plate. Surflexes are 0.125", steels 0.080". Pressure plate 0.105".

 

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Those gearbox pushrod seal kits are quite pricey and I would suggest that, most of the time, are trying to solve a problem that does not exist. When I recently had a look at my RGM Belt Drive Conversion after covering 4,800 miles I was surprised to find a substantial amount of oil sloshing around the primary cases. The colour of the oil was black. Now my gearbox is filled with a synthetic oil which is luminous green in colour so I knew that was not the source. Removing the engine pulley provided the answer. The crankshaft oil seal had partially lifted out of its housing and two of the inner chain case bolts were a little loose. A new seal, glued in place, plus some silicone on the chaincase bolts sorted out the issue.

I cannot see how oil can be pumped in serious quantities from the gearbox into the primary cases. A worn crankshaft seal will potentially cause a negative pressure in the cases which in turn might draw some oil vapour along the gearbox mainshaft. But.......you have got a pushrod, ball bearing and actuator arm mechanism obstructing the passageway plus the end of the shaft is in the outer chamber of the gearbox is well away from any thrashing gears and also well above the top surface of the oil.

Surely it must be possible to machine a grove in the pushrod to take a small oil seal similar to that on the gear change quadrant shaft?

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Yes I have read about people machining tiny grooves and using 'O' rings.

I have also read people who were quite definitive that oil was migrating from the gearbox.

All hearsay evidence.

I reckon that a pushrod which fits the hole properly, with grease would probably seal it adequately anyway. As you say, nothing to force it to migrate.

I made up my new pushrod (Commando pushrods are 1/8" longer than Dommi for the benefit of other readers) using 1/4" silver steel, not noticing at first that my original was 6mm. Maybe everybody else's are 6mm, maybe nobody!

As you say, it should be pretty easy to figure what kind of oil it is, engine or gearbox.

Anyway, I haven't been through all this grief to have oil of any kind pissing out of my chaincase.

I started my project when the only way was to put a Commando mainshaft into the gearbox to get the circlip groove, before the special Dommi clutch centres came out, How about you?

 

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Hi Steve,

              Have you had a look in archived roadholder ? Click on articles index and you will find many articles on belt drives. Several have been submitted by philip Hannam .

I fitted my RGM kit back over 10 years ago, now it seems they are improved with a narrower belt. As mentioned previously I had to pack out my outer primary cover to stop it scraping. I fitted the seal kit onto the end of the main shaft and all is dry. Prior to this there was a small amount of gearbox oil getting through. I'm told that under load the push rod flexes and acts like a skipping rope drawing oil from the gearbox. Maybe someone is pulling my leg! I will never know.

My 68 Atlas has the commando kit supplied with a longer belt and three longer stepped studs for the stator, I cannot remember if it came with a longer sleeve nut, maybe I altered the existing. It did come with a very large spring washer to go under the sleeve nut, this digs into the rotor,no way could it undo! I made a drive side adjuster out of a large socket, a button head unbrako bolt , a Commando rear brake adjuster, a fairing mounting bolt and a couple of nuts. This works well and is easy to make adjustments. If you have a lath and oxy it is simple. I can do a drawing if your interested. I'm assuming that your 99 has the same clearance between the back of the inner primary and the engine/ gearbox plate.

What has become of Mike Haworth who began this thread?

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Yes I did a fair amount of research recenty, but only rejoined the club a week ago. There are a lot of opinions out there!

I bought the special seal too, but I idly wonder if a greased, closer fitting pushrod would have achieved the same goal. No benefit to letting it flex 0.175mm that I can see.

I bought two identical stainless gearbox adjusters, but no way to reach the left one.

A sketch would be handy, I have a lathe and a welder. Part of the range of essential Norton special tools aren't they? I just finished making a couple of spacers for the rear shocker bolts this morning..

Steve  

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Hi, reading about pushrods made me remember an old trick that reduces oil coming through, and lightens the clutch lever effort. Cut the pushrod in half and reduce by  a quarter of an inch, assemble first half from the right hand end of the gearbox, put a quarter inch ball bearing in, then the other pushrod piece. I use silver steel, slightly centre drill, and heat red hot, quench, then polish, heat gently to dark yellow and quench in hydraulic oil.  It gives a lighter clutch pull, and lasts for years. Grease the ball of course. 

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Why not get the same effect by using greased 1/4" silver steel for the whole pushrod? 

Hi Andrew - I'm still here ! I have fitted a spacer between the primary chain case cover and the chain case itself. This means the chaincase cover, when bolted in position against the spacer, leaves about 1/2" of the chain case seal on view. Not pretty, but as there is no oil to be sealed in the chain case, it's purely a cosmetic issue. Inside the chain case, in the area where the wires protrude from the stator, I have glued two pieces of 3/8" thick neoprene to sit astride the wires and hopefully protect them from chafeing against the chain case cover. As I am still wrestling with a timing issue (new subject for discussion intoduced to the forum today) the bike is not running so my efforts are as yet unproven.

Mike Haworth

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With a Commando clutch you must use either the sintered plate set or the fibre plate set up, you cannot mix and match, either method the circlip should fit and allow the diaphragm to rotate freely until you loosen the compressor tool. Check and double check that circlip is correctly fitted in its groove before releasing the compressor.

Gearbox oil, use bog standard cheapest you can find EP90, I've only seen Castrol of late, but some farm stores may hold it in larger quantities in other names. The modern versions 85w-90 and the like foam like hell - for those doubters, try it, put some in your gearbox and run the bike on the centre stand with the inspection cover removed, now think of your bushes running in foam like solution. Maybe the reason why some think that modern gearbox oils eats bushes, it doesn't but maybe the way the oil functions causes more wear.  I have had oil migrate down the pushrod, but nowhere near enough to contaminate the clutch, with cheap EP90 it is remarkably less. Oil can not 'pump' down the pushrod, the push rod is not that clever and moves back and forth the same distance so could not act as a pump in one direction only. 

Most belts used in belt drives will run in oil, but I would imagine that they mean a bath of oil where contaminants can drop out to the bottom of the chaincase, a little oil on the belt could be detrimental as it would not be 'washed' by a generous supply of oil and collect wear dust and grime form the plates  making a fine paste over time - not good. 

Most modern clutch friction linings can run in oil, though I would need to check the surflex material they currently use. Even the sintered plates can run in oil, it will not harm them, but there is a different figure for the torque they can handle when they are used with oil. That figure as we know is below what the Commando can pump out. The dry design was used, if it was for oil bath use, it would need a larger / wider clutch design envelope. 

In reply to by ashley_cutler

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Hi Ashley,

                Sorry for late response - been away. You say I should use Castrol EP90 in my gearbox but the original Norton Manual I have (although it's for an '88' not a '99') it recommends SAE 40 in Summer and SAE 30 in Winter. It goes on to say "these oils should be used in engine and gearbox".

In my Haynes Manual it recommends Castrol GTX for the engine and Castrol Hypoy (doesn't give viscosity) for the gearbox.

Cnfusing !

 

Mike Haworth

 

In reply to by steve_marshall1

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Hi Steve & Mark,

                           Here ( hopefully) are 2 pics of the adjuster that I made up. I used a commando rear brake adjuster ( modified ) along with an old socket machined to fit on the big through bolt on the top gearbox mount.

                           The adjuster was welded to the socket. The large bolt was removed, put in a lath and then drilled and tapped to take a 6mm unbrako button head. This secured the adjuster to the bolt.

                            Next I drilled a hole in the gearbox cradle to mount the adjuster stop. This was an old fairing mount. The threaded rod fits through this mount and has two nuts for adjusting. I have a special ring spanner which has been "wasted" so it will fit over the rod. As you can see it is all easily accessible.

                             Sorry it has taken so long to reply. The Atlas has been hard to get at as I have been recovering after road testing Aldi's protective motorcycle wear. After a 150 meter slide down the bitumen it all passed with fling covers. not so my ribs and scapula. This wasn't on the Norton by the way.

 

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