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Primary Belt drive by Bob Newby


vibrac

Well Known and Active Website User
VOC Member
well the Comet racer was 600 plus for 3 seasons and all on belt smooth as silk
Its 500 now as you get more points for a 500
 

vincenttwin

Well Known and Active Website User
VOC Member
David
I git the 38/68 ,that is good to hear ,do you know if I will hae to shave anything of the outer cover on my Std B twin.
Thanks
Peter
 

davidd

Well Known and Active Website User
VOC Member
Peter,

From what I know, the 36 will fit with no modifications and one has been done on a Rapide. There have not been a lot of reports on the larger sizes. I would guess that the flange on the engine pulley is so large that it will impinge on the outer primary bump and you will have to make a thick gasket to gain the clearance.

David
 

johnmead

Well Known and Active Website User
Non-VOC Member
Osman Malak of the, I think, Dutch section is in the process of making primary covers that will fit the 40mm Newby beltdrive setup. We have been emailing back and forth for the last year or so and he sent me pictures of a couple of CNC covers and the last email I got from him had a picture of the first cast cover.

I have emailed him a couple of times over the last 3 months and have not gotten a response. Maybe someone in the UK or Europe will know how to contact him.

I am putting a Newby drive in a 1200 twin with Quaife 5-speed and got nuts from Bob for both the crank and clutch. I only had to machine off some of the threads on the mainshaft to fit the clutch closer to the inside of the primary. I eliminated both spacer that came with the kit and that gave me enough without grinding the engine cases.

Bob said that a 1/2 inch thick spacer would be required to use a stock cover with the clutch chamber removed. I don't know if that was for the 39mm or 40mm unit.
John Mead
 

vibrac

Well Known and Active Website User
VOC Member
john's experience seems to mirror mine although I got that extra 1/8 th futher in by making the clutch pressure plate thicker but I was interested in getting below the joint face rather than a clutch dome since I did not have one
 

vibrac

Well Known and Active Website User
VOC Member
"Its all been done before" after 60 odd years what a well oiled refrain and what a lot of reading there is
 

vincenttwin

Well Known and Active Website User
VOC Member
Trev
Since you are the guru on machining ,can I buy Bobs clutch set and rip my cover off and install it or do I need to machine a lot off the outer cover?
Thanks
Peter
 
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clevtrev

Well Known and Active Website User
VOC Member
Trev
Since you are the guru on machining ,can I buy Bobs clutch set and rip my cover off and install it or do I need to machine a lot off the outer cover?
Thanks
Peter
Have a look at the picture, and take note of the flange thickness, that abuts the case. You will find you do not need to machine anything, merely to add.
 

johnmead

Well Known and Active Website User
Non-VOC Member
However the pictures are too small to see any of the details. Even clicking on them to make them bigger, you still only get a @ 2inch x 3 inch picture. Do you have larger copies of those pictures?
 

johnmead

Well Known and Active Website User
Non-VOC Member
What is the width of the belt? The Newby kit I have has a 40mm wide belt.

John Mead
 

vincenttwin

Well Known and Active Website User
VOC Member
Trev
Yes but what about the cover T5/3 ,the belt kit I have the belt is 30mm.
Screen Shot 2013-03-27 at 8.27.37 AM.jpg
this is a photo from Bob Newbys web site ,
I am still looking for some one who has put one of these kits on to a road going bike and used the Vincent cover.
 

clevtrev

Well Known and Active Website User
VOC Member
Trev
Yes but what about the cover T5/3 ,the belt kit I have the belt is 30mm.
View attachment 1797
this is a photo from Bob Newbys web site ,
I am still looking for some one who has put one of these kits on to a road going bike and used the Vincent cover.
I can`t see that dynamo drive getting under a standard cover.
 

Spqreddie

Well Known and Active Website User
VOC Member
And Waht about the reduction ratio of the kit?
I'm planning as well to put one of those on my '48 rapide, and i remeber that when i spoke with Bob Newby he told me that he produces two versions 1: 1,8 and 1: 1,6, i guess the difference will be in the front pully number of theets and the clutch drum remains the same in both versions.
Wich would be closer to the original ratio?

I also remember that he was not sure about the cleareance of the original cover,
With the double thoothed belt, the main problem remains the generator pulley width.

Thanks,
Edmondo
 

nkt267

Well Known and Active Website User
VOC Member
Divide the number of teeth on the clutch by the number of teeth on the crankshaft pulley and that will give you the ratio..John
 

vincenttwin

Well Known and Active Website User
VOC Member
I am thinking that there is at least 2mm you could take off the back of the gen pulley and maybe up to 10mm you could take off the front of the gen pulley and maybe another few mm off the case ,
yes I think you will have to pull the primary cover to get to the gen pulley as it will never come out of the small gen pulley cover...
Also you will have to machine away where the current clutch oil seal sits and maybe some around where the belt will run.
I went with his 36/68 and gen pulley of 32 which should give it 1:8 and spin the alton a little faster than the nice plastic gear.
Peter

But so far no one has fitted one that I have to a std road bike and Patrick Godet over in France was not over enthused about the double sided belt.
 
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Spqreddie

Well Known and Active Website User
VOC Member
Divide the number of teeth on the clutch by the number of teeth on the crankshaft pulley and that will give you the ratio..John
Thanks John,
i know, but i'm away and i have not the possibility of counting the theet and i was wandering if somebody could share the ratio of the original sproket/clutch set up to see how close it is to the Newby set up.
thanks,
Edmondo
 

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