Hi Norman,
My theory on this problem is that the gears are being overoiled, and that the oil trapped between the teeth strains the teeth to the point that they eventually break.
This may sound a bit far fetched, but take a careful look at the situation. On the Mark series engines, the same gears (but 1/8" narrower) gave good service. The increase in width of the Dragonfly gears should have improved their performance - but the reverse is the case. Also, on the Dragonfly you will find there is a large cast in drain port to let the excess oil return to the crankcase - but there is only one - the oil the other side of the tunnel for the oil filter is trapped to a depth that can cause the overoiling.
I bought my Dragonfly in 1973 (in bits) and put it on the road in 1976. Just like a lot of other 'Flys, it shed it's teeth about every 5,000 miles (usually from the cam idler). At the time of the bikes second rebuild (1996), I decided to improve the oil drainage from the timing chest (having discussed the problem with other LDMCC members). This modification just requires 2 holes 5/16" dia to be drilled in the back wall of the timing chest - one each side of the tunnel for the oil filter, at a level which leaves the teeth of the cam gears just skimming the surface of the retained oil. Since doing this mod, my Dragonfly engine has covered another 30,000+ miles without any further problems. (I had the engine apart earlier this year and the gears still look good enough for another 30,000).
As I say it may sound a bit far fetched, but hydraulics can be a complicated subject, and where speed is involved, liquids can put up almost as much resistance as solids. Take even a thin liquid such as water as an example - absolutely harmless when applied gently - but put that same water in a swimming pool and do a belly-flop from the diving board - its resistance to moving can, and often does, cause serious injury. Obviously, speed is the factor which governs the liquid's resistance to change shape, so the harder you rev your engine, the greater the problem becomes - those who cruise around gently don't seem to suffer this problem.
This thinking may be a bit too lateral for some, but it has worked when applied to my Dragonfly.
Regarding the conversion to a timing chain - there was a Dragonfly at this year's Annual Rally that was reported to have such a conversion, but I don't have any further information as to how it was achieved or to the longevity of it's operation. It certainly didn't sound much different to the standard setup when it was running. From experience of the post war engines, a chain conversion on the Mark series would be relatively simple (because the mag drive is outboard of the cam drive, the chain would only have to connect the crank to the 2 camshafts), but on the Dragonfly, the chain would have to be looped back to obtain enough contact with the crankshaft sprocket and also drive the distributor.
Regards,
Eddie.