This week I at last received the magneto back for the 1928 Douglas, it has been rewound, remagnetised and repainted so I went about refitting it and of course had forgotten how the re-engage the gears so had to go back to first principles, well really.
Being a horizontally opposed twin there is a bang every half magneto revolution so first off must find which plug is firing, usually this involves electrocuting yourself but as I am a chicken I do it differently. I have an electronic magneto buzzer, it was designed to time aircraft so can do two magnetos but does one nicely, a byproduct is that when the points open the appropriate hi-tension lead tingles (tech term for mild electric shock) so not only tells you the points have just opened but which plug is firing. So having already stuck my thumb over a plug hole to find out which one was on compression and lined up the file mark on the flywheel the rest was pretty simple. These timers are available on the net, the one I use is from http://www.brewingtontech.com/ but now only available as a kit however these ones looks good http://www.skygeek.com/magneto-timing.html and shipping to Australia is only $15 USD they have single and duel magneto models with and without sound (you want sound).
While on the subject of useful stuff. I use an electronic inclinometer rather than a degree wheel (see picture below) these are about $32.00 AUD on ebay and as they are magnetic they stick anywhere to the rim of the flywheel, when at TDC hit the zero button and move the flywheel and the box is giving you a direct measurement of angle, works great for engines with no timing marks.
Lastly I had a tip from Colin a friend of mine who had to make some gaskets for an overdrive unit. He just put the part, mating surface down on his scanner and printed out the scanned image, he used thin gasket paper in his printer then just cutout the picture, you probably should scan and print a ruler first and check that it prints to scale. A photocopier may be OK as well but I take no responsibility for what the gasket paper might do to it!