The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Ewen on 25.08. 2021 04:51
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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??
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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 . . .
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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.
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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
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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
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The light works if you loosen the centre screw (if the points plate doesn’t drop off).
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*fag = cigarette in the UK
Well, mainly.
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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.
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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.
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Thanks. Interesting idea.
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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.
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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.
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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
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And the BSA setting was for real petrol not fuel so it is only a starting point at best
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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.
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I use the Magneto Guys timing light and I am very pleased with it. Initially I used it with an SRM timng disc but it is always a worry when you discover the timing is different between the cylinders even though it does not seem to cause problems in use.
Now use rod through plug hole as per the 1963 BSA service hint below.
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It is also worth mentioning that when setting the correct piston position ie BTDC you should take the piston below the correct setting then bring the piston up to BTDC this eliminates any backlash in the timing gears.
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With the plugs out, back wheel off the deck, putting the bike into 4th gear allows easy movement of the crankshaft by rotating the wheel. Go back a bit then forward to the BTDC position.
Don't forget to wedge open the arm of the auto advance unit, if there is one. The tapered end of a wooden clothes peg is a suitable wedge.
Apologies for the repeat but it is essential that you set the points gap before the timing; adjusting the gap affects the timing.
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Many a happy hour spent with a Dremmel grinding the slip ring ramps to get the timing the same on both cylinders. Whether it makes any difference??
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In the link is the buzzer I have been using for years - a handy choice for anyone in north America maybe - although they'll export to anywhere. If anyone wanted.
They come as a kit, and are keenly priced for them as don't mind a bit of not-too-hard soldering.
Useful plus is that you can synchronise 2 mags with it, so it's very popular with folk playing with aircraft, or vehicles with twin mags & plugs, like eg vintage 3 litre Bentleys.
It's a good long-lasting tool (mine's over 10 years old, and much used) and good value I reckon.
www.magnetotimer.com or
http://www.brewingtontech.com/Pictures.html
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Whether it makes any difference??
It'll make a difference Yeti, sure.
You can get 'em to 'spot-on' if you're patient and you'll get better tickover and you'll reduce risk of piston or valve trouble at higher speeds, especially on higher compression engines if there's a big difference.
Have to remember a degree on a K2F mag is 2° on the crank on any 4 stroke twin, so a small error can affect timing quite a bit.
The Question always, however, is 'Is it really the camring that is the problem?' , because it often isn't.
This irregular heartbeat thing is one of the reasons a lot of people are going Thorspark or similar these days - with which I have much sympathy despite a certain personal bias. Or, more appealing to me, the 'Joe Hunt route'. I was with a good friend yesterday who uses a scarily-tuned early 650 Triumph outfit for 'beach racing' - for which he uses a Hunt twin-spark mag. Best of all worlds maybe? I am much tempted by them as they pack a serious punch and don't look ridiculous, rather like an SR2 Lucas in fact . . . Also, all parts are available by return post from the good 'ole U S of A. I am slightly surprised not to have come across more of them over here in Europe to be honest because they are dead easy to work on and fairly bullet-proof.
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Hunts are a bit primitive Groily, in my experience. No advance or retard facility on the two I've had, and they're ugly sods too.
Not so bad on A range BSAs but on Trumpet twins they're vulnerable and weakly mounted on the timing cover.
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Ewen - if you are so inclined to DIY you could have a look at the PDF attached and (being a kiwi) source and adapt a jaycar kit (KJ8204) to make a magneto timing buzzer. I think the PDF is from the Queensland BSA owners club site from some years ago. worked for me.
tho buying the one mentioned would be less work.
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Hunts are a bit primitive Groily, in my experience. No advance or retard facility on the two I've had, and they're ugly sods too.
Not so bad on A range BSAs but on Trumpet twins they're vulnerable and weakly mounted on the timing cover.
Dunno about primitive Rex, I guess they are a bit as they're simple, but all the same they're much like most other fixed coil and magnetic rotor jobs, many of which are 'fixed' timing and need an ATD. The flange on the flanged Hunts is narrower than on a Lucas it is true, but I haven't heard of one breaking, and they're fitted to some quite hairy motors. They look pretty much like the SR2 on some later Oilfields, and a zillion base-mount SR1s on singles. Maybe they're all ugly sods!
But the real advantage is the wasted spark, and the power of the coil, especially their red 'competition' version.
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on Trumpet twins they're vulnerable and weakly mounted on the timing cover.
That would be on Unit Triumphs.
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I dont know about a kit for a buzzer, I just bought a cheap (around £0;80) buzzer from an electrical repair shop, a torch battery and a bit of wire and two small croc clips I had lying about.