BN belt drive and clutch

[Allan G]

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.

[chaz]

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he had a BNR belt , unsure of age or what to do I contacted Bob, very helpful and told me the belt was an old one and superceded by another wider one.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.

[DAVE BRADY]

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.

[Mike Farmer]

 

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

[Bess]

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...

[DAVE BRADY]

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.

[Allan G]

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.

[Bess]

Hi Allan,
           Cush drives,

Your 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...

[Allan G]

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/

[DAVE BRADY]

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.