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Primary Belt drive by Bob Newby


vincenttwin

Well Known and Active Website User
VOC Member
Any one running an belt drive kit done by Bob Newby , if so any fitting problems, any grinding of the outer cover needed.
thanks
Peter
 

vibrac

Well Known and Active Website User
VOC Member
You do not say twin or single
on a single
I have discussed this at length in the Grey Flash Diary
Bob knows the correct centers you just need to cut away about 5/8" of the inner wall surrounding the clutch in two places
follow his instructions on tension
I have never had a belt go in racing I change it every season but after the first change you have a spare
Oh and fit a crankshaft oil seal,forget chains ,oil ,vibration,clutch problems,adjustments,noise
Magic (well if you still have a Burman box -semi magic)
Twin
I fitted one to the 1275 race Egli racer had to do some mods on the length of main shaft, shaft gearbox nut and the pressure plate to get it to sit in far enough but that may have been sorted by now
Never fitted the outer cover as it was a new engine. the math went like this ((cover+standard clutch+ESA+chain+tensioner)-(bob newby kit+sheet of Alloy))=£400
at least that shows all except the clutch body sits below the joint line of the cover (see photos on www.oldracer.co.uk)
he also was playing with a double sided belt to also drive the dynamo rather than the 'sprocket from hell' not sure where that has got to (let us all know )
he is most approachable so ring him
 

vincenttwin

Well Known and Active Website User
VOC Member
Thanks road going twin. Yes Bob has the two sided belt now and a nice pulley instead of the nasty plastic gear that eats it self from time to time.. getting ready next month to install and was hoping some one had already done one.
IMG_1732.jpg
 
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davidd

Well Known and Active Website User
VOC Member
Bob uses a bigger clutch on the twin than the single. The single clutch will fit in the single case. I think that someone wrote on this forum that they had to space out the primary cover on the twin.

David
 

vibrac

Well Known and Active Website User
VOC Member
Yes that may have been why I did a bit of work on the shaft and nut to bring the belt edge below the joint face so I could fit a flat alloy plate with a big hole for the clutch. It was not a big job mainly to clear the shaft/nut protusion inside the clutch basket against the pressure plate after modifying the shaft and nut I added about 1/8" alloy plate to the pressure plate with countersunk allen screws to get that last bit of clearance. I suppose if thats is seen as a lot of work and the belt is proud of the joint face a spacer around the cover is the other way. (thats what I had to do with my 52 Trophy to clear the clutch with a pattern chaincase) but setting the clutch that bit further back if you can just looks neater
 
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vincenttwin

Well Known and Active Website User
VOC Member
Bob's clutch is a little less than 3" thick. he sells it as a replacement for the vincent clutch ,all I could get from Bob was you might need to grind a little away from the outer cover.??
 

Gerry Clarke

Active Website User
VOC Member
If it's for a road going motorcycle, is there no shock absorber anywhere in the primary drive?

Gerry
 

vincenttwin

Well Known and Active Website User
VOC Member
Bob Newby says the rubber belt more than makes up for the lack of the nasty little springs.
 

davidd

Well Known and Active Website User
VOC Member
Gerry,

I know it sounds odd, but the belt does quite a good job and there is no need of a shock absorber. Carleton Palmer and I have run these very hard for over a decade and there is no penalty for not having a shock absorber. I suppose the ability to slip the clutch with little or no damage helps tremendously. I have run mine for 12 years without changing a plate, but it is a single. I will be very interested to see how well it works on the twin.

02/13/2020 I justs reread this post again and although what I say is mostly true I believe that I should have mentioned that the use on the track is not the best indicator of use on the street. In in this case, starting at stop signs and lights is where you get the greatest shock. The belt does not provide any shock relief in this case. I know there are street bikes that use belts, but they belts should not be confused with a shock absorber.

David
 
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Gerry Clarke

Active Website User
VOC Member
Thank you David. A composite belt drive is not universally considered an adequate substitute for an independent cush. I was discouraged from fitting a BNR drive to a BSA road single by Phil Pearson who uses belts for racing - fine for racing, but harsh pottering at very low revs. on a roadster was the conventional wisdom in that particular application.

Gerry
 

vibrac

Well Known and Active Website User
VOC Member
the tension of a belt is important too tight and indeed if you are pottering at low revs it may in the end give trouble
tensioned correctly its far superior and dont forget removing the primary chaincase and inspecting without oil is a doddle. and a new belt costs a lot less than a chain.
I can see I shall have to put one on the trials comet "hash pottering at low revs"? thats about the only time... :)
 

vincenttwin

Well Known and Active Website User
VOC Member
Still no real answer if it will fit inside an std primary case ,has any one fitted one to an road bike.
 

Glenliman

Well Known and Active Website User
VOC Member
I had Bob make me up a setup for the 1360 Terry Prince motor, but haven't assembled that yet. He supplied it with 7 thnner plate rather than the standard five, just to be on the safe side. He also ordered the double toothed belt in a custom length in order to make the hub sizes such that the primary ratio is nearly the same as standard Vincent. Prior to this he used a stock size double toothed belt which required hubs sizes that turned the trans slower than std Vincent, thereby putting greater torque on the trans.
I ordered a spare belt for the drive as this double toothed custom length affair is not going to be available at a hardware store in Mooserump Saskatchewan, should he belt let go out on the road. Roy Robertson has one of Bob's belt drives on his Egli. He did manage to break one belt, but that was after about ten years of sprints, roadracing and speed record chasing.
I have to say that in section the double toothed belt looks pretty flimsy, but hopefully there is adequate strength in the centre section..

Glen
 
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Glenliman

Well Known and Active Website User
VOC Member
Forgot to address the primary cover question. First, I should mention that I will need to remove some material from the inside of the new Molnar cases in order to get the clutch drum with belt to clear. As far as the cover goes, I also could not get a clear answer from Bob as to whether it will fit or not, or whether it required ventilation or not. His response to the question was that " a belt will always run cooler than a chain in a given situation" or words to that effect. I would like to run the standard cover, without ventilation, because this is a road bike and I'm quite sure that an open racing type cover will allow road grit and grime to get in the primary.
I might compromise and use a standard cover but cut some smallish vents for and aft, will likely fit screens to those in order to keep out the big chunks.

Glen
 
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davidd

Well Known and Active Website User
VOC Member
Thank you David. A composite belt drive is not universally considered an adequate substitute for an independent cush. I was discouraged from fitting a BNR drive to a BSA road single by Phil Pearson who uses belts for racing - fine for racing, but harsh pottering at very low revs. on a roadster was the conventional wisdom in that particular application.

Gerry
I believe the statement, but I have never experienced it. I have pottered arround the pits quite a bit, stopping and starting for pedestrians and traffic. I have only 1/2' of foam for a seat and I have never felt any type of harshness. I also know two other Vincent owners that have belt drives on their street machines, one on a BSA and the other on a Parkin single. I will enquire, but in the past decade, they have never mentioned any harshness.

David
 

davidd

Well Known and Active Website User
VOC Member
Forgot to address the primary cover question. First, I should mention that I will need to remove some material from the inside of the new Molnar cases in order to get the clutch drum with belt to clear. As far as the cover goes, I also could not get a clear answer from Bob as to whether it will fit or not, or whether it required ventilation or not. His response to the question was that " a belt will always run cooler than a chain in a given situation" or words to that effect. I would like to run the standard cover, without ventilation, because this is a road bike and I'm quite sure that an open racing type cover will allow road grit and grime to get in the primary.
I might compromise and use a standard cover but cut some smallish vents for and aft, will likely fit screens to those in order to keep out the big chunks.

Glen
Glen,

I have been racing with a completely englosed cover in the last season of racing and I would not consider this high risk. I suspect a cooling air flow would do more for the clutch than the belt. I think it was Roland Pike that discovered that a primary chain drive used about 2 hp of energy that is efficiently turned into heat. Carleton Palmer ran an unventilated stock primary cover on his Flash for years with a belt.

Personally, I would run it closed. Pebbles will cause a belt to break in a nanosecond. If vented, screens would be a "must".

David
 

Gerry Clarke

Active Website User
VOC Member
David,

That sounds good - can't beat personal experience. It may be that the smoother power impulses of the vee-twin make it a better candidate for non-cush belt drive than a big single.

Gerry
 

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