Belt drive questions (2006)

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Oct 16, 2006
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Hi

I have a belt drive from Les Emery,

does anybody have experience of the belt stretching? either my belt has stretched a lot or my final drive chain has...after not many miles I have run out of adjustment on the chain adjusters. I really look after my chain so I would be pretty surprised if it is chain wear, though if its not the chain it must be the belt, I guess.

The other thing that I have noticed about this belt drive is that the clutch drum does not fit perfectly squarely on the end of the gearbox input shaft, the top of the drum can be seen to move in and out by a couple of mm as it rotates. At first I thought the shaft was bent but I am now sure it is not. Maybe this is all within the tolerance of the set up? I'd welcome your comments on this.

Thanks, Alex
 
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You have bought a new product with a warranty (ok its Norvil but there is consumer law) so you are best contacting Les as trying to fix it yourself is going to void any warranty.

If you want to investigate further have you fitted gearbox adjusters on both sides, belt drives need them to stop it moving the gearbox forward, do hope Les told you this like RGM do and included it in your kit.
 
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belt drive

Hi O. G. Biker,
Chain or belt, the primary drive adjustment will affect the rear chain adjustment. However, once the primary is adjusted and the transmission is properly secured the rear chain adjustment has NOTHING to do will the primary. The belt drive manufacturers recommend to dual transmission adjusters in order to pull the tranny back more squarely, but, it can be done without them. The RGM kit tells you to use the rear chain in order to pull the primary belt into adjustment, secure the transmission, then readjust your rear chain accordingly. I'd wager your rear chain is just starting to go to hell.

GB
 
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The belt don't stretch. It must be set very loose cold like one inch free play minimum. If this sets the transmission adjusters way back from the old setting you may find a loose drive chain. Did you get the bottom trans bolt very tight? If you didn't the trans can slip back also loosening the drive chain. And at the same time tightening the belt, a bad thing. Time to recheck the whole thing.
Good news is you won't need to move the trans for a long time once it's set. Clutch basket wobble, is the clip behind the basket letting go? You did use a new one right? The bearing in the basket can do this too. It's hard to find one that is tight enough to keep this to a minimum.
This is why I wish RGM still made their special primary cover for belts that had the out rigger bearing out on the cover.
 
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In a very non-technical mood....

A Norton pal who knows his bidnness, a guy in the next state from where I live, recently wrote me and said, "We always ran a belt primary on the race track, but I personally have never run one on the street. They aren't hard to set up, just remember to set them up loose, cause they get tight after being run. In fact, it is good to check them hot, to make sure they don't get too tight."

Makes sense. Not sure if it helps in your situation. Just thought I'd pass it along.

kevin
 
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I have for quite some time been running one of Les Emery's belt drive kits on my cafe racer commando with only one adjuster fitted and have experienced no problems at all. My bike has a 4s cam, gas flowed and skimmed head, 32mm carbs etc. etc. so it's probably producing a whopping 1.3 additional HP over standard! However it is genuinely at the upper end of performance for a 750. I have noticed that the primary adjuster is almost at it's maximum setting but as Norbsa pointed out once adjusted they do not stretch. If your final drive-chain is relatively new you may simply need to remove a link from it. If it's got a few thousand miles on it then it may be time for a change, a new chain is a lot cheaper than a new sprocket/brake drum assembly. Norbsa is also correct in pointing out that the locating circlip on the gearbox shaft is quite fragile and should be checked and if neccesary changed any time you have the clutch drum off. An important point that has been stated before (I think by L.A.B. our irreplaceable repository of lost wisdom of the ancient's) is that the book-specified 70ft/lb torque setting on the clutch hub retaining nut is about 30 ft/lb over the point at which this circlip can shear and the recomended specification is I believe 40ft/lb (Can you confirm L.A.B.?) So if this has sheared your hub may well be wobbling due to an eccentric seating.
 

L.A.B.

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dave M said:
the book-specified 70ft/lb torque setting on the clutch hub retaining nut is about 30 ft/lb over the point at which this circlip can shear and the recomended specification is I believe 40ft/lb (Can you confirm L.A.B.?) So if this has sheared your hub may well be wobbling due to an eccentric seating.

I dont think it was me who actually raised the point before, but this would certainly appear to be true according to Les Emery at Norvil:
http://www.norvilmotorcycle.co.uk/techtalk16.htm .


L.A.B. our irreplaceable repository of lost wisdom of the ancient's

I've been called some things in my time, but that's a new one!
However I shall indeed take it as a compliment -Thank you!
 
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old grey biker said:
....I have a belt drive from Les Emery, does anybody have experience of the belt stretching? either my belt has stretched a lot or my final drive chain has...after not many miles I have run out of adjustment on the chain adjusters. I really look after my chain so I would be pretty surprised if it is chain wear, though if its not the chain it must be the belt, I guess.
Alex,
the belt doesn't stretch noticeably, and thus doesn't change it's length. If you have adjusted the belt's tension by moving the garbox reaward in the subframe, your final drive chain jhas lost it's proper tension.

old grey biker said:
The other thing that I have noticed about this belt drive is that the clutch drum does not fit perfectly squarely on the end of the gearbox input shaft, the top of the drum can be seen to move in and out by a couple of mm as it rotates. At first I thought the shaft was bent but I am now sure it is not. Maybe this is all within the tolerance of the set up? I'd welcome your comments on this.
The clutch drum doesn't sit directly on the main shaft, but on the clutch centre to which it is connected via a sealed roller bearing. It enables the clutch basket (outer sprocket) to rotate freely on the clutch centre when the clutch lever is pulled (disengaging clutch plates). If your clutch basket "tumbles" then it is most likely that this bearing isn't properly seated within the clutch drum. Take out the clutch assembly and find out if

a) the circlip holding the sealed bearing is in situ and OK
b) there is excessive lateral play of the centre within the clutch basket
c) the clutch basket spins freely on the centre w/o any drag

If a), b) and c) look and feel OK, you should also see to that the circlip(s). collar and spacer(s) on the main shaft behind the clutch are in situ - when you thighten down the clutch centre nut, then the clutch assembly is seated squarely against them.
 
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Firstly I want to thank everyone who replied, it is really good of so many people to take the trouble to go into so much detail.

I have had this belt drive for a couple of years but only noticed the loose chain recently after rebuilding the gearbox.

I am using only one gearbox adjuster and should probably go to two on the basis that there can be no downside once it is fitted. Unlike RGM Les Emery does not push this mod too much for road bikes.

The simple answer is to remove a link or two from the final drive... but I didn't want to do that if the primary belt had stretched for some reason (I would have bought a new belt, motorcycles are the only one thing in my life where money is no object!).

Regarding the clutch drum run out, the circlip behind the clutch drum is new, as is the mainshaft, the run out appeared on both the old mainshaft and the new mainshaft...Les Emery suggested the mainshaft was bent when I discussed this with him - leading me to rebuild the gearbox with a new mainshaft - which made no difference, it still runs out.

The clutch outer turns on the inner without any run out, this leads me to discount a misalignmnet in the bearing. I can also say with 99% certainty that the mainshaft is straight since I examined it in great detail before fitting it. Therefore the run out can only be due to the clutch inner not sitting squarely against the circlip. It is a very tight fit to get onto the mainshaft.

Of course, this may not be a problem, I've probably done at least 5000 miles with this wobble in the clutch. But the small part of me which is the perfectionist/engineer is considering the following...

freeze the mainshaft and heat the clutch inner before fitting to see if I can get a better location against the circlip,

or

take some emery paper to the inside splines of the clutch inner to make it a slightly looser fit onto the mainshaft.

I'd welcome your comments.

All the best

Alex
 
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old grey biker said:
I have had this belt drive for a couple of years but only noticed the loose chain recently after rebuilding the gearbox.
Alex,
that seems to tell almost the whole story ....... :cry:

old grey biker said:
I am using only one gearbox adjuster and should probably go to two on the basis that there can be no downside once it is fitted. Unlike RGM Les Emery does not push this mod too much for road bikes.
If the gearbox sits tight & squarely (mainshaft and crankshaft parallel) with this set-up, I am afraid that won't get you anywhere regarding clutch "wobble". But an outrigger mainshaft bearing supporting the mainshaft (eg as sold by steve Maney) might help to minimise mainshaft flexing under load.

old grey biker said:
The simple answer is to remove a link or two from the final drive... but I didn't want to do that if the primary belt had stretched for some reason.
Regarding belt lengthening, all I can tell you is that I used a Norvil 40mm ("race") belt drive kit for 4 years and it never stretched a bit.... running dry & cool in a generously ventilated primary case. However, this might not have been the case with a slimmer 30mm (road") belt.

old grey biker said:
Regarding the clutch drum run out, the circlip behind the clutch drum is new, as is the mainshaft, the run out appeared on both the old mainshaft and the new mainshaft...Les Emery suggested the mainshaft was bent when I discussed this with him - leading me to rebuild the gearbox with a new mainshaft - which made no difference, it still runs out.
This confuses me a bit ..... you're saying, the problem had even occured before you had the new mainshaft fitted? If so, then the "wobbling clutch" could have worn out your belt considerably. Does it show any wear on it's inner (toothed) side, most likely an "uneven" one?

old grey biker said:
The clutch outer turns on the inner without any run out, this leads me to discount a misalignmnet in the bearing. I can also say with 99% certainty that the mainshaft is straight since I examined it in great detail before fitting it. Therefore the run out can only be due to the clutch inner not sitting squarely against the circlip. It is a very tight fit to get onto the mainshaft.
This seems to isolate the problem down to the clutch centre - certain batches of these parts were known to be either insufficiently hardened, excentric, inner bore ill-machined and out of angle (askew), our generally out of tolerance specs (wrong inner dia & length). The clutch centre should definitely slide easily onto the mainshaft rigth down against the washers and the circlip, and should sit there with a minimum of play!

old grey biker said:
Of course, this may not be a problem, I've probably done at least 5000 miles with this wobble in the clutch. But the small part of me which is the perfectionist/engineer is considering the following...
An ill-centered clutch centre is a problem, it does actually stress mainshaft and belt in an unduly manner, and can thus cause premature belt wear. I think what happened is that your new mainshaft has made an old problem more obvious!

old grey biker said:
..... freeze the mainshaft and heat the clutch inner before fitting to see if I can get a better location against the circlip,
or
take some emery paper to the inside splines of the clutch inner to make it a slightly looser fit onto the mainshaft.
I'd rather try out a new clutch centre, which should be a perfect fit. And, of course, replace the old belt that has been tortured by clutch "wobble" for a couple of years.....
 
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what is the general rule of thumb for setting the tension of the belt?

thanks

Mark
 
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fourperf said:
what is the general rule of thumb for setting the tension of the belt?
Mark,
my 40mm wide black (HTD) belt worked flawlessly with a vertical play of approx. 1" (1/2" up and down) of the lower portion (upper one stretched out flat).
However, recommended tensioning values may vary due to belt sizes (width), belt materials and types. The typical "Gates" type belts with a "round" cross-sectional tooth shape are quite tolerant regarding slack, run very smooth and don't wear out noticeably, whereas belt drives with a "trapezoid" cross-sectional tooth shape (sharply edged theeth) seem to be more critical tension-wise. Hope this is of help.
 
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brittwin said:
fourperf said:
what is the general rule of thumb for setting the tension of the belt?
Mark,
my 40mm wide black (HTD) belt worked flawlessly with a vertical play of approx. 1" (1/2" up and down) of the lower portion (upper one stretched out flat).
However, recommended tensioning values may vary due to belt sizes (width), belt materials and types. The typical "Gates" type belts with a "round" cross-sectional tooth shape are quite tolerant regarding slack, run very smooth and don't wear out noticeably, whereas belt drives with a "trapezoid" cross-sectional tooth shape (sharply edged theeth) seem to be more critical tension-wise. Hope this is of help.

thanks brittwin

I have a 30mm belt.

right now it is tensioned in such a way that I can twist it to an angle of 45 degrees in the middle of the belt

Mark
 
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As you do I ignored the Norvil instructions and tensioned mine by the 45 degree method. Now it depends how much force is applied to do that but I overdid it and when the clutch drum and crank pulley expanded I had a bowstring tight belt with a poor functioning clutch. Norvil recommend 33mm (1.3") total which makes for a very loose belt cold and some primary clatter but it's about right when hot. A suitable diameter socket with a tight fit between the belt and top boss on the inner case works.
The 45 deg trick only works for automotive cam belts (temporary measure) and machine drives IMO.
 
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I"m going to revive this thread since my clutch troubles may lead to replacing the clutch to a lighter action model and since the primary is open, I might as well do the belt drive conversion.

I have been told to get a Norvil belt drive by the fine folks at CNW. he has used many, including RGM and mentioned I should go Norvil.

Any fitment horror stories I should know about? I have never done any work to my MkIII yet so this will basically devirginize me as it will be the first project I undertake.

I assume I have to rip everything apart to get a centre to centre measurement for belt size ect. There are also a lot of pulley size options for the Norvil kits so I don't really know where to begin. I don't race and will be using the bike as a daily driver. I would like a bit more pep if possible but stock is ok. An engine rebuild is in the picture next winter but no ultra perfromance upgrades. Maybe a flowed or ported head and a bit of a zippier cam, but that would be about it.

Is something for a pro techinician or should I be able to do it over a weekend? As long as I have good instructions, I am confident I can do it. I do not however have a clutch tool. Suggestions?
 
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Coco said:
I"m going to revive this thread since my clutch troubles may lead to replacing the clutch to a lighter action model and since the primary is open, I might as well do the belt drive conversion.
Coco,
the only way to achieve a "lighter" clutch action is to use a softer diaphragm spring (not recommended). However, if you ensure minimal clutch cable friction and if you polish the clutch pushrod appropriately, the clutch should be easy on your left hand.

Coco said:
I have been told to get a Norvil belt drive by the fine folks at CNW. he has used many, including RGM and mentioned I should go Norvil.
Good advice, IMHO. The Norvil belts are of the HTD "Gates" type with round teeth - they run very smooth, but must not be used in an oil bath. There is one kit of 30mm belt width available which allows for retaining the electric starter (sprag) mechanism, but I doubt that occasional greasing thereof will suffice to keep it alive in an otherwise dry primary chaincase. If you want to dispose of the e-start, you may go for one of the pre-Mk.III belt kits (also of 30mm belt width). Their 30mm crankshaft pulleys ensure that the alternat0r rotor doesn't unduly protrude outwards - which is the case with the 40mm belt kit, thus necessitating the removal of the ignition timing indicator segment plate (06-4694) from the inner side of the outer chain case. Is is also a good idea to discard the bronze-type clutch friction plates, and to order a set of "surflex" plates to replace them. And, yes, two additional plain steel plates should come in quite handy - one goes to the backplate of the clutch basket, and an additional one might be needed on the outer (spring) side to get the thinner "surflex" plates packed up tightly.

Coco said:
Any fitment horror stories I should know about? I have never done any work to my MkIII yet so this will basically devirginize me as it will be the first project I undertake.
You'll need a sprocket extractor to take off the original crankshaft sprocket, the clutch compressor tool, and the clutch locking tool. You should also be prepared to find the original crankshaft pulley a tight (taper) fit, secured (against rotation) by a woodruff ("half-moon") key. Heating it up will make this job easier.
Before fitting the new alloy pulley, you'll have to clean the crankshaft taper appropriately of old Loctite residues (solvent, emery cloth). You'll also have to heat up the alloy pulley to approx. 150°C before you tap it home onto the crankshaft taper (w/woodruff key in situ and a little Loctite). The same goes for the fitting of the (sealed) clutch bearing - heat the clutch basket before you tap home the (generously greased) bearing.

Coco said:
I assume I have to rip everything apart to get a centre to centre measurement for belt size ect. There are also a lot of pulley size options for the Norvil kits so I don't really know where to begin. I don't race and will be using the bike as a daily driver. I would like a bit more pep if possible but stock is ok. An engine rebuild is in the picture next winter but no ultra perfromance upgrades. Maybe a flowed or ported head and a bit of a zippier cam, but that would be about it.
To measure the distance between crankshaft and gearbox mainshaft (centre to centre) you don't need to take the primary drive apart. Yes, there are plenty of pulley/clutch basket sizes available, since there's only a choice of two belt sizes (990mm and 920mm). The pulley/clutch basket combo you'll get might thus be not the same as that of the original primary transmission ratio, but you may recitify any such matters by selecting a smaller or larger mainshaft (final drive) sprocket.

Coco said:
Is something for a pro techinician or should I be able to do it over a weekend? As long as I have good instructions, I am confident I can do it. I do not however have a clutch tool. Suggestions?
Since this is a "first" for you, you'll be able to do it over a weekend - a "pro" could do it within 2 hours. All you'll need to have is the workshop manual(s), the apropriate tools (clutch tool and sprocket pullers are a must!), the belt drive kit fitting instructions, and a little patience. Hope this is of help to you.
 

L.A.B.

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brittwin said:
the only way to achieve a "lighter" clutch action is to use a softer diaphragm spring

That is not correct, as the amount of force required to pull the clutch spring which should result in it going over-centre (and therefore reduces the amount of pulling force necessary) can be varied by adjusting the clutch plate stack height.

A well set up Commando clutch should not be particularly heavy to start with, and should get lighter as the lever is pulled.

http://www.oldbritts.com/ob_clutch_info.html

http://atlanticgreen.com/clutchpak.htm

There is also a graph showing the force reduction included in the NOC Service Notes.
 
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L.A.B. said:
brittwin said:
the only way to achieve a "lighter" clutch action is to use a softer diaphragm spring

That is not correct, as the amount of force required to pull the clutch spring which should result in it going over-centre (and therefore reduces the amount of pulling force necessary) can be varied by adjusting the clutch plate stack height.

A well set up Commando clutch should not be particularly heavy to start with, and should get lighter as the lever is pulled.

http://www.oldbritts.com/ob_clutch_info.html

http://atlanticgreen.com/clutchpak.htm

There is also a graph showing the force reduction included in the NOC Service Notes.

Thanks L.A.B.!
 
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L.A.B. said:
That is not correct, as the amount of force required to pull the clutch spring which should result in it going over-centre (and therefore reduces the amount of pulling force necessary) .....
That's what I assumed - as well as a well-oiled, not overly bent clutch cable and a clean pushrod...... and taken all this for granted, the "last resort" is a somewhat softer diaphragm spring ..... :wink:

L.A.B. said:
.....can be varied by adjusting the clutch plate stack height.
I have advised "Coco" to use one or two extra steel plates to that end.

L.A.B. said:
A well set up Commando clutch should not be particularly heavy to start with, and should get lighter as the lever is pulled.
Yep. It's not of the same "feel" as the typical modern hydraulic Hoyasuka type, but by no means unduly "heavy".
 
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