BN belt drive and clutch

[DAVE BRADY]

Good morning,

What about the cush drive?  The BNR belt drive/clutch set up does not have a shock absorber so does this feel snatchy at low revs? 

Dave.

[RICH]

Low revs??
No seriously, I have fitted BNR belt drives to my Spitfire scrambler and my Super Rocket.
I cannot say I noticed any snatching. A very well engineered piece of kit.
I shall be putting a set on my early A7SS in the near future.
If you do fit one make sure you have the belt slack enough.

Rich

[Mike Farmer]

 

Thats very interesting. I'm about to go down that route and hadn't even considered snatch.

Mike

[DAVE BRADY]

Hi,

I believe the shock absorber in the primary drive plays an important role in smoothing things out at lower engine speeds and when shutting/opening the throttle, taking strain off the chain, splines, clutch plate tangs etc.  Nortons diaphragm clutches have no shock absorber but there is one in the rear wheel. I think some Harleys have one built in to the front drive pulley.  Hayward belt drives utilise the original clutch centre so why nothing in the BN clutch?  Probably intended for racing where a shock absorber may not be necessary but when in in conversation with a reputable A65 racer the opinion was that it made the transmission quite harsh and that the triplex chain was preferred.
I know several people on this forum, apart from Rich, use the BN setup so what are their views?

Dave

[Bess]

Hi,
    I have them on a A10 and A65.

On the A10 I slip the clutch more with the belt drive when taking off, I have gone up a tooth on the final sprocket and the belt drive ratio is greater, good for cruising. I had to ensure adjustment was as the instructions plus a little more. When the engine was hot the expansion made the belt too tight and the gear change became difficult.

There is no instruction and adjustment on the A65. I have the standard gearing and still slip the clutch on take off a little more but no other issues.

I bought damaged casings and cut ventilation holes to stop condensation. I do find fine surface rust on the plates if the bikes are laid up and have been tempted to take them out over the worst of the winter months but at the moment start the bikes regularly.

Best wishes...

[idie]

I have just done a rebuild on a friends A10 which was fitted with a belt drive. He always thought that the drive was harsh. Having changed to a 4 spring clutch the difference was very noticeable. In case you were wondering why we changed, the clutch was dragging. This turned out to be the bearing in the back being stiff.

[Mike Farmer]

 

So questions for those who have this system.

Is it an easy job to fit--is it any easier than a normal clutch. What do you consider to be the benefits. What do you consider to be disadvantages if any. Does it justify the cost AND would you recommend it?

Mike

[Bess]

Hi Mike,

Really easy to fit on the A10. A65 I had to change the alternator studs so a little trickier.
PROS - No oil, better gear changing and selecting neutral, quieter, no chain to adjust, cut holes in the primary case, find your artistic self, look young and cool.
CONS - No cushioning so a little harsher feel when taking off.
Doesn't justify the cost, however I got loads of money to waste since the COVID lock-down.
Yes I would recommend it, but worth looking at alternatives with integral cushion.

ps enjoyed your story in the Star this month, glad to hear you got satisfaction.

Best wishes...

[DAVE BRADY]

Good afternoon,

I have been playing with HTS-2000 again so some pictures at some point.
So a cleaver person with a bit machinery could probably adapt a cushdrive clutch centre to be a front pulley for a BN belt drive.  This person is not me as I only have a pillar drill and some big hammers.

Dave.

[ducati2242]

Not Bob Newby but my belt drive is very smooth . No snatching at all .

[Mike Farmer]

 

So if not BN what are the alternatives.

Mike

[Mike Farmer]

 

Hi Bess.

That wasn't me, but I too offer my congrats. I often don't pursue the smaller items---I don't think that it justifies the time. But certainly go for it on anything a bit expensive.

Mike

[DAVE BRADY]

Hi,

Phil Pearson offers an NEB belt drive which does not appear to have a shock absorber and then there is the Haywood one utilising a Triumph clutch centre.  I think, however that for A10s etc. SRM do a front pulley that allows the use of the standard spring shock absorber.  So a few alternatives.

Dave.

Just found this.  An NEB belt drive.

[Allan G]

My bike originally came with the Hayward kit and I refused to use it, if it's of interest to you Dave you can have it, it needs the melted bits of belt scraping off and a new belt buying (dpo fitted the belt with the chain tensioner adjuster but not the blade, so the hex cut its way through the belt)

I run the BNR now, I will have 3 kits by the time the oif is built, 1 racing setup and the others are his 5 plate setup (the standard being 4) I have given that clutch more punishment than the stock unit would ever handle, the bikes been started from standing in top gear, and slipped in gear to about 5k (I won't go into why), the clutch has even been "dropped" from a standing start which picked the front end up (again the old 3 spring unit wouldn't cope with that)

Another good thing about it is I've just had to remove my gearbox because of a selecting issue (not clutch related) it took an hour from a complete bike to box out and on the bench, vastly helped by a impact gun and being able to remove the clutch basket without having to drop any oil from the primary, and 6 clutch adjusting screws, one central nut (as normal) and a 2 jaw puller with M8 bolts to remove it.

The only thing I will say is my 68 didn't have a problem but the beefier cases on my 71 meant I had to dremel away some of the alternator housing to give clearance for the 36t pulley. Unlike the Hayward the BNR has guides on both Sides of the pully, the basket is wider so that there is no centring issues.

Only "down side" is the alternator is stepped out by about 10mm, it comes with all the bits to achieve this but it means that your timing pin cannot be left in the primary cover as it would foul the rotor.

Also the 36:70 drive ratio is like adding another tooth to your gearbox output sprocket.

[DAVE BRADY]

Morning Allan,

I am not putting a Hayward kit back on my 750 as I would not trust the belt so I have one sitting on a shelf.  I may use it in another engine at some point but probably not.
The only problem with the standard clutches seems to be the inadequate bearing that even when new has wobble and the fact that they can take a bit of setting up.  I believe that they can take anything a belt can as for a long time the chain was the only option for road, race, drag etc.   
Undoubtedly a catastrophic failure of a chain is likely to cause more damage than a belt but they last so much longer   when properly set up and adjusted which is needed just as much for the belt.  A chain will, even without proper adjustment, last for quite while whereas a belt will not.
What I find disappointing with the belt kits is that they are not made with the standard ratio and some times need cases to be ground away to fit.  That to me is 'garden shed' engineering.  Also, no shock absorber for A65s.  Why?  Although it is probably claimed that the belt acts as a shock absorber I bet the belt would have a much easier life if one was used.  Also, on the A65 the need to keep the tensioner.  Having to adjust the belt tension even if only once is surely a potential problem.  Surely a bespoke front pulley could be made to negate the need for this and why not incorporate a shock absorber in to this? 

Dave.