How effective are they? And how do they work?
I run a standard one on my racer and it's always a bit of a hassle to set up the chain tension. I have a cut away timing cover, but an auto one sounds great.
Are they reliable, bearing in mind that the motor goes to 7000rpm at every gearchange!
RMA's works from under the chain providing constant tension via a spring pushing a heel that rubs the chain. It requires engine case mods. I have only heard of one failing in an over rev. It was replaced by the maker.
Kelly Cork in Australia makes one that fits inside the chain rubs from inside out. It is a modifiyed car part that has a rachet machinism .030 incerments. it rubs but not as hard and requiers no case mods.
I run both types in my two Commando's they both work well. A norton without one suffers from timming that is not as smooth as it could be with one.
In the US the cost is about the same with shipping so just choose.
I have an RMA model on an early Cam-shaft breather motor which I am building at the moment so I have not actually run it yet although it is fitted. The instructions indicate that you may have to file a flat of about 2 mm on the inside of one of the timing side crankcase bosses where the screws that hold the timing cover on go. I did NOT have to do this on mine but you could easily do it with the motor in-situ in a couple of minutes with a hand file.