Primary belt life

25,000 miles? Here's mine at that mileage, about 10 weeksago. Yes it does get dusty in the primary even if they are set up to run as near as dammit perfectly aligned. Mine has also seen oil when it shouldn't, has been cleaned in solvent when it shouldn't have been and was to be replaced. My own fault really. If yours still looks ok with no major fraying or rubber chunks in there and it's run slack when cold, you should be good for at least my mileage.

David, I run mine with a 30mm socket snugly wedged between top run and inner cover boss as a test (see pic.) Norvil do state 33mm but I felt it was a bit loose. 20mm does seem tight cold as that drum really expands. Have you noticed the clutch lever freeplay increase when hot?

Around 15 years ago Andy Dunn, the former NOC Tech Advisor, showed me the Belt Drive Conversion he had on his Commando. His advice was to slacken off the belt until you could just push it inwards across the top of the clutch pulley using only a little finger. This gave the belt roughly 30 to 35mm play in the centre of the top run. His view was that it was better to have a slightly slacker belt than run the risk of an over-tightened belt shedding its teeth.

From later conversations with many other owners of both race and standard bikes, who were using belt primary drives, his advice appeared sound. The general view being that belts should have a life of 25 to 30 thousand miles wear before a renewal needs to be considered.

However, these numbers aregreatlyreduced if:-

* the belt is allowed to run for long periods in extreme heat

* It is too tight

* it is rubbing against a pulley keeper due to misalignment

* it gets contaminated by solvents

In the USA many Commando owners, withbelt drive, add cooling vents to theirprimary cases to help keep the components cool. I fitted belt drives to both a 650SS and an Atlas. I noticed that the belts always became drum tight after a long run due to the expansion of the alloy engine and clutch pulleys. The suggestion from the supplier was to set 40mm play in the belt rather than the 30mm in the fitting instructions. This, however, caused another problem. On a cold start-up there was then too much play in the belt which whipped and started to catch on the alternator carrier. I guess the solution to this would be a 'car' type of tensioner.