Ignition Timing
Posted by
hendred on
May 28, 2020; 10:24am
URL: http://silk-motorcycles.221.s1.nabble.com/Ignition-Timing-tp5001920.html
When I got my Silk running some years back I set the ignition timing as per the handbook method (I am still using the Lumenition system). Recommissioned the bike last week and decided to check the timing again as it hadn't been touched for years. It was spot on using the handbook method. After calling Clive on another matter, we got round to ignition timing and he suggested checking the advance mechanism was working correctly. So removed the alternator cover and marked up the tdc and advance positions. Connected strobe and started engine. The running advance was about 3 - 4 degrees less than the static. Must be backlash in the mechanism. Easily corrected. I was also interested in engine speed for full advance and on my set up it is 2200 rpm. Has anybody else checked their mechanical advance and what speed did you get?
The performance on the road has been transformed. Before it was very peaky, only really getting going at over 5000 rpm. Now it pulls very well from quite low rpm. Much more fun to ride!
The handbook quotes ignition advance by piston position in most places, the trigonometry isn't difficult to convert to degrees of rotation, just repetitive and boring. Found this little program on the internet for calculating crank rotation from piston travel:
http://www.torqsoft.net/piston-position.htmlI believe the con rod length of the Silk is 130.5mm and stroke 72mm. Put in the numbers and it will convert piston position to degrees of rotation or degrees of rotation to piston position. Quite interesting results. One place in the handbook quotes 37.5 degrees of advance with 0.3 inch of piston travel - put 72mm stroke and 7.6mm (=0.3") in the boxes and the con rod would need to be 1 metre long to get 37.5 degrees! I'll stick to setting the ignition by marking up the alternator rotor and stator from piston position and using a strobe - works well on my engine.
Always learn something new when messing around with old bikes!