1940 Royal Enfield J2 on the workbench.

Currently receiving attention in the workshop at the moment is this 1940 Royal Enfield J2 500cc. The last time I used it was a couple of years ago when it set fire to itself and nearly me too. The bike had come to a sputtering halt at a roundabout, I had suspected that the timing had slipped but I gave it a test prod on the kickstart anyway, it gave an almighty kickback and began self immolation. The bike had a full tank, I knew I didn't have time to get off it and put it on the stand (it only has a rear wheel stand and is very heavy) so I stayed astride and puffed and flapped with my hands. Only by miracle did the blaze cease. After that it was put to the back of the garage in shame for a while - the automotive equivalent of the naughty corner.

The bike was exported to India from new, presumably to a British Officer out there as the War was already on. I brought it back home a few years ago and then sold it to a friend locally. He did a bit of work on it, put it on the road and then a few years on it ended up back in my hands. Seems like it should really be back on the road for the summer.

Royal Enfield J2 timing side. A handsome motor.

Stripping the timing cover off I found that there is way too much backlash in the timing gears, specifically the gap between the idler and magneto pinions. No amount of adjustment of the mag strap would fix it and over the years someone has had a go by packing out the tail of the mag to lower the pinion slightly, not good practice but not a real problem in the real world. All the same this bodge didn't cure the problem. 

I've got a couple of spare Magdynos on the shelf so compared the one fitted to my spares. Strangely the platform on the mag fitted was a mil or so higher than on the spares. I swapped them around and the backlash has largely gone, or at least it is now within tolerable levels where it is possible to time the bike correctly and not risk slippage. I was never aware that the platform height could vary on a Lucas Magdyno.

Next stage is get it all back together and test run on the open road. Of which more, no doubt, to come...

Ill-fitting Magdyno.

Primary side. As can be seen the bike is a scruff or characterful
depending on point of view!

Nice fitting Magdyno. Now cross fingers the spark is strong
enough...