The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: Superarnie on 26.07. 2023 17:44
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Today, after a full strip down restoration on my 1960 Spitfire Scrambler, I got to the stage of turning the fuel on, turned the ignition switch to on, and after 4 kicks it burst into life. What a racket though!! Neighbours aren't going to be happy!. The engine sounded fantastic, with no indication of pinking or misfiring. I was really please. Now during the restoration I fitted the Thorspark Electronic Ignition system, and after the start up procedure, you are to check the timing with a strobe light. So I put a timing disc from SRM on the end of the drive side crank and a needle pointer attached to the engine drive side case and checked the timing. At low revs the timing looks to fluctuate around the 5-10 degrees BTDC. However as I revved the engine the timing pointer didn't seem to move . Throughout the rev range the engine sounded great but I was concerned the ignition didn't advance. I am wondering if the auto advance may be stuck in the retarded position? Incidentally when I was doing the restoration, I lubricated the auto advance and put new springs on it and it seemed to function quite freely. I'm wondering if there is something I should have done when I fitted the auto advance unit. Can anyone give me any advice in this regard, I'm not to clever with this stuff.
Many thanks
Gary
Ps I tried to attach a video of the initial start up but it was rejected because the file was too large!
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G'day Gary.
Sounds like the problem. With the timing cover off can you move the auto advance unit and see the other end move as well? The new springs may be too strong. It should reach full advance at about 2500rpm. Does your timing light tell you the rpm?
With the timing fluctuating 5-10 degrees would indicate the mag bearings aren't the best allowing the shaft to oscillate (wobble).
Post the video on youtube and put a link in here.
Cheers
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Thanks Muskrat,
Can you explain in simple terms how the auto advance works.
I have read on this forum of people with points ignition, installing the auto advance and having to hold the bob weights out ( with wooden chocks) as they set the points in position (I may read that wrong though) but if that is the case, I'm wondering if I should have done such a thing during the installation of my electronic pick up?
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http://www.brightsparkmagnetos.com/faqs/FAQs%20about%20ATDs/How%20does%20an%20ATD%20work.htm
This might help?
And look too at the Priory Magnetos site where there's the best description of why they seem sometimes to be misbehaving even when they aren't.
Not sure what the Thorspark instructions say about fitting, but that system relies on the ATD (or manual cable arrangement) certainly, as there's nothing built-in.
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Thanks Bill that link was very useful.
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When I want to show a video to the forum I put it on YouTube and then copy the link and paste that into my forum post.
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G'day Gary.
I've never worked on a Thorspark system but would assume if it uses the ATD for advance it would be done the same as the normal points system.
Remove the ATD, set the Thorspark marks, wedge the ATD to full advance and push it on the mag shaft. Take care the shaft doesn't move when you do the nut up. Fine adjustment should be possible at the Thorspark marks.
Bills link is excellent.
Cheers
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G'day everyone.
By way of update, you may remember that from initial start up after a full restoration, the timing didn't advance with increased revs. I took the side timing cover off to discover the breather top hat had slipped off the timing sprocket dowel and the cork washer was destroyed. I have replaced the top hat, inner timing cover and timing sprocket and refitted a new cork washer of what I believe to now be the correct thickness. Whilst completing that work I removed the auto advance/retard unit and found it was functioning correctly and freely and was well lubricated. Incidentally, when I restored the auto advance during the restoration and put on new springs. I have since re started the engine and got the carb settings about right. On checking the timing disc fitted to the drivers side crank with a strobe light, I noticed at full advance the timing is hitting 33 BTDC, however as the revs drop down to idle, the strobe is flashing at 20 BTDC which I think is about 10 degrees too advanced. Can anyone give me advice as to why this may be. I'm thinking the advance unit springs are too weak and are not pulling the bob weights in sufficiently enough. Does that sound feasible and if so, can you buy stronger (maybe shorter) springs. If not this, what else could be causing the problem. Many thanks
Gary
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20* may sound too much, but isn't really - it'll not 'pink' at tickover' and, when starting, will return to full retard due to friction of the mag as the engine starts to turn it.
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The range of the ATD is 11 - 13 degrees so it seems that your unit is spot on.
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Thank you both for your responses. Trevinoz, is that range of 11-13 degree of the ATD, equivalent to double that at the crank. If so, 33 at the crank should reduce to around 7 to 11 at idle, on the crank? Or am I misunderstanding. My idle at crank is 20 and 33 at max advance.
Many thanks for your help.
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The ATD range should indeed be 11-13° on the magneto if the correct unit is fitted (Lucas part # 47503A/E for what it's worth), so it is double on the crank, yes.
Sounds as if yours isn't retarding properly as you say. Whether because the springs aren't up to it or because the mechanism has some sort of mechanical defect causing it to stick.
One thing you could do is wire the driven and driving members together at full retard and test run it - without moving your timing disc from the position it's in - to see what difference it makes. (You could then lock it fully advanced for that matter, to prove the actual operating range.)
Fitting stronger springs may well do the trick, but I'd check to see what rpm were then required to get to full advance. Typically, your ATD should be at full advance around 1150 magneto rpm, 2300 engine, and would be fully retarded when engine rpm dropped to about 1500. A bit either way won't kill anything obviously, and the actual firing point at full retard isn't mission critical provided you get a reasonable tickover. Significant spring pre-load could, however, delay getting to full advance by several hundred rpm.
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Thank you, that's very helpful.
If I do require stronger springs, are they available? If so do you know of a supplier/part number. Presumably the springs are rated, what rating would you recommend? I've no idea what I've currently got as I just bought them directly from some magneto parts supplier on the Internet.
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Afraid I don't know about the rating of the springs or the options. I have seen springs for distributor advance and retard systems used in error though, and maybe also sold by unknowing vendors to unsuspecting punters.
I think a PM to Andrew at Priory Magnetos (Cheeserbeezer on here) might be a plan. He knows these things better than I do and probably (almost certainly) has any bits, correct ones, that you might need. Also is an expert on fixing the darn things . . .
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Thanks Grolly, I'll give him a call.