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andersonjThu Nov-06-03 06:43 PM

  
"Belt Drive Options for non Commandos"


  

          

Greetings,

I am thinking about fitting a belt drive to my 500 Dommie used in pre 63 Classic racing down here in New Zealand. (Reasons : weight, easier on motor, no oil leaks, cheaper in the long run than chain replacements)

Our rules do not allow more modern clutches so I need to stick with the AMC clutch. Most of the commercialy available belt drive kits converted to Commando style clutches.

RGM sell a belt drive kit which keeps the original clutch but having read Dave's piece on fitting a RGM kit to an Atlas Im wondering if there is a better option out there.

I have talked to Mike Hemmings and he could make one but would prefer to sell a few and not just one.

So does anyone have any ideas. Currently Im leaning toward the RGM one expecting it will need a lot of work to fit it properly.

Any thoughts appreciated.

John

  

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dynodaveFri Nov-07-03 01:13 PM
Member since Mar 18th 2009
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#1. "RE: Belt Drive Options for non Commandos"
In response to Reply # 0


  

          

Curious to know if it has to simply be a "coil" spring clutch or the "original" 3 coils and original plates? There may be more options if you don't have to have the genuine original clutch. What do you have to retain to be original/legal?

As you may well know, my attempted atlas conversion was with the commando diaphragm clutch, with a narrow front pulley and a long belt. It may still work with a better bearing and new gearbox/sleeve gear bushes.

  

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andersonjSun Nov-09-03 01:59 PM

  
#2. "RE: Belt Drive Options for non Commandos"
In response to Reply # 1


  

          

Hi Dave,

I didnt realize it was an attempted conversion. I hoped you had been sucessful. Makes me a bit more concerned about having a go.

The clutch question is a bit grey. The rules say you must use a period clutch (pre 63) but there not always followed. Anyway I dont want to spend a lot of money and get it protested so I want to stay with the AMC clutch. It works fine when it is dry and is plenty good enough for a 500.

Had a bit of difficult weekend . The bike finished 3 races but way back and Im sure the mag is still wrong. All day I had a misfire above 6000 and the bike would not pull clean at all. I got passed by iron engined BSA on the straight so definitly something is unhappy. The gear shift went as well so Id come into a corner go down to third and then go for 2nd and it wasnt there !!! I missed 20 times more gears in one day than in the previous 3 years.

Our next meeting is not until early Feb so time to do a few things before then. Racing wears things out infinitely faster than riding on the road.

I now have all the bits from Morris mags including a new rotor and coil. They have been very helpful

Cheers

John

  

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dynodaveSun Nov-09-03 05:30 PM
Member since Mar 18th 2009
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#3. "RE: Belt Drive Options for non Commandos"
In response to Reply # 2
Sun Nov-09-03 05:33 PM by dynodave

  

          

Hi John
I_did_drive on the road with the RGM/AT10 belt drive. With the atlas release cam it was a pinkie finger commando clutch. I think the combination of a set of worn sleeve gear bushes and possibly a brand of ball bearing, that did not hold the clutch drum straight.
With the primary cover off I could SEE the clutch drum twist under load and then the belt would crawl sideways.
I then put the chain back on to finish the engine break-in (which failed). I will fix up the gearbox and clutch hardware and try again, once I put an engine that "I" build.
If the domi main shaft allows flex due to the lack of rigidity on the splines, I may switch to a commando mainshaft and see what happens. The conversion commando/domi clutch center is really only held by the "flat washer" within the clutch center, at the end of the domi shaft. The flat washer could be flexing....
The commando clutch center is located between the circlip and the center nut, and is a better arangement.

I was wondering if you could have used one of those 6? coil spring suzucki clutch belt drives.

DAve

  

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andersonjMon Nov-10-03 10:27 PM

  
#4. "RE: Belt Drive Options for non Commandos"
In response to Reply # 3


  

          

Thanks Dave,

Yes one of the guys here also suggested thinking about changing the Dommie mainshft to a Commando one to get more rigidity. I forgot to mention it. I havent looked at all the bits side by side to see what would fit but I think your idea is a good one.I havnt been inside a Commando clutch for years so I have forgotten what it looks like but I will have a look at the workshop manual to remind myself of the differences. On the Dommie even with the narrow chain line at the back of the clutch drum there is still fair bit of twisting. With a belt centre line sitting further out on the clutch there would be a lot of torque on the splines. A Japanese clutch would be against the rules.

However after last weekend I seem to have a pile of things to fix already just get back to where I already was so maybe this development is going to have to wait a few months.

After inspecting the bike I have the following list, rebuild mag, a quick check on the head and cam timing needed, the front suspension is sticking and bouncing under hard braking, the longer carb mounts for inlet tuning need strenghtening, Ive got a fuel pipe issue with the new tank, the gear indexing seems to have gone and beleive it or not the swinging arm bearing has now gone.All this on a bike I thought was ready to go.

This trying to race old bikes is harder than it looks !! I'm getting slower and less reliable !!! I think the only thing I havent replaced is the steering head bearing. That must be due next week !

John

  

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andersonjMon Nov-17-03 05:17 PM

  
#5. "RE: Belt Drive Options for non Commandos"
In response to Reply # 4


  

          

Hi Dave
I have found an RGM kit lying in dusty corner at Britishspares plus someone who has got one working on a 650 so we shall have a go sometime in December. The guy who put it on the 650 had to change the aligment. It was a fair bit of work.

Ill let you know how it goes

Cheers

John

  

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dynodaveTue Nov-18-03 11:21 AM
Member since Mar 18th 2009
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#6. "RE: Belt Drive Options for non Commandos"
In response to Reply # 5


  

          

John
What kind of clutch center?...commando or modified "commando" with a welded in washer(for domi shaft). You will probably need a longer 25mm belt.

Dave
Prepping for grinding the exhaust ramps on the norvil 2S (domi core) camshaft.

  

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andersonjTue Nov-18-03 10:45 PM

  
#7. "RE: Belt Drive Options for non Commandos"
In response to Reply # 6


  

          

Hi Dave,

Dont know yet. The guy who is doing most of it works part time at Britishspares so he will get what ever bits he can find around the place to make it work. They have lots of new and second hand bits available. (His usual job is fettleing all the bits from their suppliers before they sell them to customers so that can do the job they were supposed to do in the first place.)

He will pull it apart and look at the RGM kit and then go round the place looking for bits to get it to work best.

Im not a machinist, my skills stop at assembling (and drilling oil and gas wells) so will leave modifications mostly up to him. I will report on the final result however.

Heading into summer here. A bit of a lull in the race season until February. The guest rider at this year's Pukekohe festival in Feb will be John Surtees. He is bringing out an MV.

Regards

John

  

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andersonjWed Feb-11-04 02:16 PM

  
#8. "RE: Belt Drive Options for non Commandos"
In response to Reply # 7


  

          

A bit more news on this exercise.

The RGM belt is installed . The set up is standard AMC ie late 50s Dommie clutch centre which is slotted for the plain steel plates and RGM clutch basket outer which is slotted for the friction plates.

Everything lines up OK now and the belt runs straight.

However two issues have emerged.

Firstly maintaining belt adjustment. The gearbox adjuster is standard with the locking nut adjuster on the righthand side of the bike. Under racing conditions the gearbox would not stay in place and the belt got very tight. (More than just heating up). This is very surprising because I have never had a problem with the chain drive set up moving. I fixed it temporarily by filing a piece of steel to jam in the adjusting slot in the engine plate so the box couldn't move back. Asking around this has happened on other bikes here and is usually found with alloy or dural engine plates. Most go to adjusters both sides and make up a piece of alloy to fit in the slot once the adjustment is correct.

But this may be a side issue caused by the main problem. The clutch dragged like crazy. Dave you found runout to be bad and I have a simmilar but much lesser problem but combined with some worn plates I had a massive clutch drag problem. The extra width of the belt twisted the basket causing the friction plates to bind in the drum. I ran it maybe 10 mins on the track and I already have grooves worn in the outer clutch basket (alloy).

So after a day of trying we ripped the whole lot off and went back to chain drive for the rest of the weekend.

Now we will further investigate the run out and fix it but Im seeking thoughts on the following. There is a sidecar here with a AMC clutch set up and belt drive. It is very powerful machine and has been in development some ten years. It is Australasian Champion in its class.

They do not use the slots in the outer basket because they found they could not stop wear. What they did was machined half rounds for roll pins in the outer basket which then fit into half rounds in the friction plates. The roll pins go right through to the back of the clutch outer basket. They got a whole lot of alloy plates lazer cut and got friction material bounded on. This set up does not wear and has lasted several years without problems in the sidecar.The clutch action is excellent.

Dave any thoughts on downsides on this. (apart from the money)

Waht was left of the weekend after all that went fine. The rebuilt mag with Morris mag parts was great and bike happily revs through to 7000 plus. Had a small problem with fuel starvation. I had made very long rubber inlet runners and they were vibrating too much. We could see this on the dyno. Bike would accelerate great and run fine on short straights but hesitated at the end of long straights. Fuel starvation, tank venting, fuel pipe sizing, blocked filters etc immediately come to mind and were checked. The problem only went away with shorter alloy runners. So I need to make up some longer manifolds from alloy on the lath.

Hope things are good up in the winter / spring north.

John




  

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dynodaveWed Feb-11-04 02:50 PM
Member since Mar 18th 2009
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#9. "RE: Belt Drive Options for non Commandos"
In response to Reply # 8


  

          

If I'm correct, the dowel pin spline style is standard on the american mfg. and the Haywood clutches.
I'm not sure if the clutch basket flex is related to lack of support due to the AMC clutch center "washer" mount style. A lot of the belt hangs beyond this mounting plane and induces a stiff loading. The commando clutch center is squeezed from both ends. Nut on one end, and circlip/washer on the other. So it is much better supported.
For adjustment...
We sometimes use little short plates bolted to the engine plates. One hole for the G-box through bolt and the second in 5/16", an inch forward of the slot. Get a few plates in .050" length increments and once you find the right one it should not move....ever
Dave

  

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andersonjWed Feb-11-04 06:50 PM

  
#10. "RE: Belt Drive Options for non Commandos"
In response to Reply # 9


  

          

Thanks Dave

Didn't know about the Haywood drive mechanism. So in theory roll pins should work but the lack of support for the clutch centre is a concern. As I said earlier the rules prevent use of a more modern Commando clutch. My hope is that I will be able to cure it as I know of at least two street bikes - a Dommie 500 on a sidecar and a 650 which have successfully used the system. I shall talk again to the guy who did those conversions.

(I do not know the details of what is inside the racing sidecar clutch. Suspect there is not much in there which came from Norton/AMC. !!)

Thanks

John

  

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andersjmWed Jan-04-06 07:28 PM

  
#11. "RE: Belt Drive Options for non Commandos"
In response to Reply # 9


  

          

A final nail in the coffin of a very old thread.

My original intention was to fit a belt drive to a 500 Dommie using the original clutch internals. The bike was used for Pre 1963 classic racing in New Zealand and at the time our rules specified the clutch as a major component and therefore it needed to be pre 1963. (Yes - I know there were no belt drives in 1963 but the club had decided to make an exception.)

I bought an RGM belt drive which used the old clutch internals and then spent months wasting time trying to get it to work. Some very good engineers (not me) worked on it modifying various bits and getting clearances perfect.

In the end the club changed the rules. I put on a Commando style unit sourced from Australia and it was perfect from day one.

The most frustrating thing was another engineer here did get his RGM kit to work. In fact he was one of the guys who rode from Beijing to Holland and he used the clutch for that trip. But he is a very good engineer, raced Manx Nortons for years, he was a mechanic for a top three finisher at Daytona, his bikes have won several NZ titles.

So unless you are that good buy a Commando style clutch if you want to go belt drive.

The problem was that the roller bearings are right at the back of the clutch basket. The belt runs completly outboard of the bearing and no matter how well I aligned everything and no matter how much slack I put in the belt the clutch drum would twist and the clutch would drag. The clutch was not supported well enough on the rollers to stay parallel. A chain is much narrower and the chain centre line sits over the roller bearings.

On a commando option there is a proper sealed bearing in the clutch centre and there is no twisting.

  

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