Forum

[bigpete]

A lot of small jap bikes had no adjustable back plate, and so the only way to adjust the timing was by the points gap, also my bsa A50 only had one adjustable plate so you had to juggle the points gap on both sets of points to get the timing right. cheers Pete

[Les H]

If you want to know exactly just fit a timing disc on the crank end (primary chain case removed) and a small wattage 12 volt bulb on the points-to-coil wire feed. Rotate the engine until the light goes out and make a note against a pointer reference (you don't need to set the disc accurately any rotational position will do as long as it doesn't slip). Then make your points adjustment and do the same rotation of the engine until the light goes out again and make another note of the degrees from the timing disc....Subtract the difference and you have your answer and you can check with different settings....Note I am assuming you have coil ignition?...With a mag it is not advisable to stray much from the recommended gap (all to do with coinciding with the highest magnetic flux pulse on the armature)..Also note the bigger the gap the more wear will occur on the heel of the points....Les

[Dennis C]

I just want to know why Presto needs to open the points 5 thou?.

[Beezabryan]

Because he can Dennis

[Presto]

Thanks guys - between you you've answered most of what I was needing to know. In answer to Dennis C, I don't: the question was theoretical rather than practical.

[Dennis C]

Thanks for the honest answer Presto, the short answer is, yes it would have a significant affect on the timing.

[jefrs]

Set points gap to standard then mark radially on the cam where it 'just opens' (test lamp). Now increase gap to +0.005-in and mark on the cam where that 'just opens'. The difference in angle is (proportional, two spins, 720°) the increased advance.

[PeteF]

Jefrs, that would do it IF you could accurately mark the cam. Degree disk on the crankshaft and then the test lamp would be easier and more accurate.

[jefrs]

A timing degree disc/plate was my suggestion above. Marking the cam ideally engineer's blue and a scribe but a fine tip Sharpie marker can do it, and a protractor. The later might be a case of using tools to hand, the former might require tools bought.

I do have a timing strobe but someone borrowed my timing degree plate years ago, they're kinda fiddly to use.

[jefrs]

Permanent marker tends to wipe off near oily stuff. Tippex seems to stay on but is easy to scratch off with a fingernail. Ordinary white enamel paint tends to stay on too well. There are a few fine point paint pens out there (for electronics etc) that work very well if you use them all the time but if you don't use them they dry up.