Concensus on belt Drive Primary

I only use a chain primary drive (Chainman's duplex). Don't wish to use a belt drive for several reasons.

There are differing opinions about belt v chain and you are definitely NOT going to hear a "general consensus"!

As RM, only use Duplex Merc timing chain, Commando, T120 and B44. 

Belt is lighter which is of benefit to the gearbox as well as overall. And there's no oil to leak or encourage clutch slip. On the other hand, a chain works and, given you already have one, considerably cheaper. Cooling can be a problem with a belt and cutting holes in the primary cover is non-original and unsightly. The 850 Mk3 electric start is not compatible with a belt.

Both are reliable - when properly set up.

My choice would be belt for racing, chain for road.

Gearbox alignment can be addressed by fitting adjusters on both ends of the top bolt. Bit fiddly but you can then 'twist' the gearbox as needed to bring the shafts into line. Most owners don't bother and don't have a problem. Just make sure the top and bottom bolts are fully tightened.

I've seen more machines disabled at NOC rallies with shredded belts than all the other problems put together. That doesn't mean they can't be reliable, but why do it ?

The only reason I would fit a belt would be to get a better clutch  to replace the crude old dommy one.  If however you have  spent enough time  to sort out the thing and are happy with it ,then  no point. 

I can only tell you my experiences with a belt drive on the Commando, my machine felt immediately better with an RGM belt. I wouldn't go back to a chain, as for the belt shredding I'll wager the crank/clutch pulleys were not correctly aligned. I check mine from time to time which is a ten minute job. It has been there 20+ years without a problem. 

All of my bikes, less the final one, a Dommie racer, to be completed but running have chain primaries. The only issue I ever had was about 20 years ago when the split link broke on my 16H.. This was found to be it catching on the inner chain case. All in all I'm happy with chain primary and most of my cases are leak proof too. SAE 20 not so common though.

The Dommie racer has an RGM belt drive and clutch but because of the DVLA  go slow, I don't know if I will ever get it registered to put on some mileage and report back. I just thought it would be something to have an example of belt drive. But as Richard says; I too have seen a few with 'melted or broken elastic bands.' Still, as a static it wont matter.....

The recently published Heavy Twins Compendium/Compilation version 2.2, contains a bundle of articles about Belt Drive conversions. It is accesible via the News Section above right.

I have run quite a number of Nortons with a belt drive primary. Had a couple wear thin where the pulleys were not aligned correctly or the gearbox output bearings worn but never had one break. 

I found that the secret of longevity was good ventilation for the alloy pulleys (especially on a Commando) and to ensure the belt  tension was correct. Never too tight. The latest generation of Kevlar reinforced belts are almost unbreakable.

My Mk2 came with a belt drive but after is shredded again taking out another new alternator, I fitted the chain set up back on which had come with the bike while I awaited delivery of a replacement belt presuming it had been replaced with the belt drive because of primary oil leeks. The primary didn`t leek so the chain is still on there 8 years later. I think the belts jumped off due to the side guide plates being too small diameter and me not wanting to have the belt too tight as someone I know snapped a crank by having the belt drive too tight. I`m sure they can be reliable if meticulously set up but as Richard says, most primary disasters seem to involve belts rather than chains.

Told you that you wouldn't get a "general consensus"!

I think there is and it favours chains.  My garage votes 8 -1.......

I am reminded of advice given by a Land Rover expedition guru. When asked about modifications for round the world journeys he said "Leave it standard. Every modification makes it more difficult to repair". I don't suppose many Nortons are likely to shred a belt half way across Africa but he has a point.  

Good choice!