Light for points opening.

[Ewen]

Hi guys
Excuse my ignorance. I have made a circuit, continuity tester out of an old torch. When I touch the 2 alligator clips together the bulb lights. If I connect one clip to each side of the points the light remains on regardless of whether the points are open or shut. So my question... do the points not act as a switch? Surely at some point one side of the points must be isolated from the other side??

[groily]

Not quite so Ewen. The points do act as a switch, but on a magneto there is always continuity because the points are across the low tension coil of the mag, which has a very small resistance of about half an ohm. So a bulb stays lit. You need a specially-designed device or a very sensitive ohmmeter which will show the difference - the latter is hard because many meters aren't good at such low levels, and there's no guarantee there's zero resistance across the points when they are closed anyway, although it's desirable of course!
Or do it the 'old way' with a slip of thin cigarette paper to determine the moment they start to open  . . .

[Rex]

I use a piece of 1 thou shim stock about 5mm by 35mm between the points and held horizontally, and when they start to open the shim droops like an old semaphore railway signal.

[Sav]

Ditto on the shim use. I just set the timing a tiny tiny bit early based on the shim moving.

You can buy a detector that spots the change in resistance, friend of mine has one, says it's good.

https://www.themagnetoguys.co.uk/magneto-static-timing-light

[Greybeard]

I have used my digital meter to show the small difference in resistance but fag* paper works fine. I have a packet of Rizla's in my shed.

*fag = cigarette in the UK

[Triton Thrasher]

The light works if you loosen the centre screw (if the points plate doesn’t drop off).

[RDfella]

*fag = cigarette in the UK

Well, mainly.

[Yeti]

A Buzzer is much better, If you connect a buzzer across the points the pitch changes as the points open Its much easier than looking at a meter. Or for that matter playing around with a Fag (paper) in a dark garage.

[groily]

The light works if you loosen the centre screw (if the points plate doesn’t drop off).

Tis very true. but often, even if the plate stays on, it's slightly slackened and the points opening moment moves a tad.
A non-conducting - ie hard plastic - substitute screw with 3BA thread is a useful way forward if determined to use a battery and bulb. Buzzers are good though.

[Ewen]

Thanks. Interesting idea.

[Minto]

I remove the 1thou blade from my feeler gauge set and put it between the contacts, which conveniently slips and falls out as the points open.

[Ewen]

Maybe a spring setup would be good with say a rubber band pulling on whatever you have slipped between the points. That would free up one hand. If  you did the timing before you put the primary chain cover on you could use one of the holes to attach a piece of wire. Being able to turn the crankshaft directly might be usaful as well.

[Colsbeeza]

Hi Ewen,
I obtained one of those Magneto guys devices. It allows degree setting to within tight limits - I think less than a half degree. One very experienced member Orabanda has dyno-tested a Golden Flash and found the optimum setting is point opening at 30 Deg BTDC - best torque and no pinking.
To keep it all in perspective, these bikes have been set by cig paper ( +/- 1 deg) and a stick down the plug hole ( +/- another 2 deg) since the dawn of time to BSA's recommended 5/16" or 32Deg BTDC and satisfactory for most people, so all depends on how fussy you want to be.
Col

[BSA_54A10]

And the BSA setting was for real petrol not fuel so it is only a starting point at best

[Yeti]

The old fashioned but effective way of setting timing is set till you are just getting pinking and then back it off a fraction. As passed on to me by an engineer who specialised in building race engines. I tend to go with a Buzzer a razor blade and an old pushrod. Its a lot less faffing about.