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.
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
:) :) :)
Thats very interesting. I'm about to go down that route and hadn't even considered snatch.
Mike 8) 8) 8)
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
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...
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.
:) :) :)
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 8) 8) 8) 8)
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...
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.
Not Bob Newby but my belt drive is very smooth . No snatching at all .
:) :) :)
So if not BN what are the alternatives.
Mike 8) 8) 8)
:) :) :)
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 8) 8) 8)
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.
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.
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.
Hi Dave, I wasn't complete in my assesment of the Newby kit, unlike the haywood you don't need the tensioner. on a unit twin its fit and forget in that respect
(sorry this is bullet pointed)
The belts used on the BNR is a continental branded belt, much the same composition as some belts used on cars but 30mm wide and only teeth on one side. The hayward belts seem to have a life span, Ive never heard of a BNR one breaking but I have heard of hayward kits breaking when you least expect it.
Re- the shock absorber. These kits as I understand were developped for racing initially, then road versions with a lower ratio were made, the race version is a lesser toothed basket and a bigger front pully than the road kit. The basket is much lighter and the front pully is lighter too, adding weight to either of these would put you back a step, although I beleive if it was required then it would have been implemented. The kit on mine has done about 7000 miles so far, so not as much as I would have liked.
In addition I like the gearing up effect, the 823 im building will have 21-47 final drive sprockets, this is still easy pulling on a stock A65, my 68 has 19-42 gearing so I can keep gearing the bike higher if it needed it, the road BNR kit is like adding another tooth to that gearbox sprocket, for me the bike runs fine on it (its like having 20-42 gearing) so I like the geared up effect from it.
Whilst modification is required (easier if your doing this at the same time as building the motor as you can properly clean any swarf) its only the OIF it seems to need this on, if you have an earlier bike (my 68 for example) needed no modification. those with the studs for the alternator mounting would have an easier time still. If your running the race kit then you'd have to remove the housing altogether.
I think as these come under the "Performance upgrade" bracket, some DIY work to make things fit 100% is sometimes expected.
I rebuilt a Triumoh 650 for a customer, he had a BNR belt , unsure of age or what to do I contacted Bob, very helpful and told me the belt was an old one and superceded by another wider one. he asked for my pulley back and remachined it to accept the wider belt he also supplied. no adjustment needed and apparently the composition of the belt means it wont stretch.
If I could be bothered I might look at getting three, one for the Triumph and two for the BSA's , it would do away with primary oil leaks but its the finances against miles ridden.
Hi,
So back to a fundamental question. Does the belt serve as a shock absorber or is the transmission more harsh at certain revs., powering on, powering off and running at lowish speed like in queueing/slow traffic.
Dave.
:) :) :)
Well gents,
I have to say that all the comments have thrown a whole new light on this subject.
In truth my thoughts now are that there appears to be very little to recommend it over the standard triplex chain. I've never heard of one breaking, but I suppose it happens. However the amount of miles my machine will travel I can't justify it.
Except of course for the point that Bess made about making the casing pretty. I guess that I can live without that.
So thanks to all and enjoy the freedom of the moment.
Mike 8) 8) 8)
Hi Dave,
The belt will not act as a shock absorber, its toothed and constructed like a timing belt so stretch is designed out of its properties. Its characteristics at slow speed are "fun harsh" and unforgiving compared to a standard clutch, but you should adapt.
I put them on both the A10 and A65 because the existing clutches were in a bad way so the extra expense wasn't an issue, I'm glad I did for all the reasons stated earlier in the thread. I agree with Mike regrading the mileage issue, I wouldn't if I was low mileage, I would have used what I had.
If you're in the Westcounty drop in and take one of mine out and decide for yourself.
Best wishes...
Hi Bess,
Thanks for the offer but I am just south of the Humber Bridge. Your comment re shock absorbing qualities of a belt are as I suspected. My high mileage A65 has only had two chains in over 100,000 miles so I am quite happy to run a chain but the rest of the clutch is getting bit worn hence the investigation in to a belt drive as a replacement. The long stroke 750 A65 I am getting back on the road came to me with a Hayward belt drive but they do not get the best feed back and I do not think that any belt will last as long as a chain.
I have put together an early 4 spring clutch with a new BSA clutch basket, new BSA plain plates and friction plates so I am going to give that a go. Once set up it should prove to be as good as it can be but will it cope with the extra 100ccs? We will have to see.
Dave.
The 4 spring clutch was a good unit but expensive to manufacture compared to the 3 spring version. I got fed up with the constant maintenance with the 3 spring unit, I'd get the clutch right then soon as I started getting more power from the bike it'd start letting me down again. I don't find the clutch harsh, when they are brand new I found it was a little, the clutch would want to grip at every opportunity, after some hammer I can feed the clutch in with no Ill effects. It's never slipped on me once. Also how many people "dump the clutch" and expect it not to have any effect, whether it has a Cush drive or not. Your car doesnt have one and you'd never think about what you would gain with having one fitted.
Hi Allan,
Cush drives,
QuoteYour car doesnt have one and you'd never think about what you would gain with having one fitted.
Not sure this is correct, please see the image of a car clutch plate.
Best wishes...
Probably started a topic drift now, I fitted many clutches as a mechanic and never asked nor really cared for what those springs were for. Infact the only reference I could find was via the euro parts website about dual mass clutches... it discusses vibration for their reason of use, but looking at the makeup of the clutch it could just as easily also mean "Cush drive"
(Image too big so here's the link)
https://www.eeuroparts.com/blog/single-mass-vs-dual-mass-flywheel-why-convert/
Good morning,
Yes. The move to the 3 spring clutch was a retrograde step but definitely cheaper to make and it was used in the Triumph so cheaper again. However, my 650 although for most of the high mileage had low compression pistons has the 3 spring clutch and for the most part has been trouble free. Even hill starting on steep Alpine passes with a 21t gearbox sprocket and loaded with camping gear did not cause a problem. Obviously never completely perfect but only occasionally needing the springs screwing in a bit more and I think only 2 sets of friction plates in all the miles I have done. Perhaps with some new bits in I will stick (not slip) with it for another 100,000 miles (in my dreams).
I think I will start a new thread.
Dave.