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Deleted User.
Deleted UserHi everyone. I’m looking for some advice on what to do about my magneto. Tha problem is that the spark looks weak to me and the bike does take some kicking up, but eventually goes and seems to run O.K. I’ve tried cleaning and resetting the points with only a small improvement. The slip ring looks OK but that’s as far as I’ve gone.
Am I looking at a full refurb and if so does anyone have any recomendations. From a previous newsletter, I note that Roger had some bad experiences on rebuilt mags but , gentleman that he is, didn’t point the finger. The bike is a 1947 F.S. with a DPY engine and it’s at least 20 years since the mag was last reconditioned, so doesn’t owe me anything.
One other thing, if run in the dark with the points cover off, you can see the points sparking. Does that mean the capacitor has gone?
All advice gratefully received.
Tony Kitching
Deleted UserHello Tony i have allways thought on the Scott as a mag test bed and have on a few ocasions had mags refurbed . If you have the time you could try remagnetising and fitting a condencer but if no cure it can lead to a rewind etc . I gues the best advice is a refurb . Afriend had a first class job from Dave Lindsley his ad is in old bike mart.hope this is of help.Regards D F.
Deleted UserGave up on re-furbished mags as lets face it they are getting long in the tooth and work fairly hard on a Scott ! Most of the parts are also well picked over by now and the novelty of swapping mags every few months has worn off ! Remedy ?…Fitted a NEW BTH and it has been money well spent. Starting is now best ever, performance is better than ever, and was the easiest to fit and set ignition timing. Did find that this electronic mag needed less advance that the old Lucas (Prince of Darkness) and a weaker mixture as well. So better all round plus better fuel economy. 😀
Regards Peter Scott , South Australia
Deleted UserWhen I start a restoration job, the first thing I start with is the magneto. You can rest assured that something is wrong with it, especially if it is a Lucas Magdyno. The original armature was insulated with shellac, which after a few seasons will crack and become hydroscopic. The result is shorted secondary windings and a weak spark. The factory seldom used more than 8000 secondary windings, but there is room for ca. 12000, which will give a much more healthy spark. If the armature is insulated the modern way with oven-baked epoxy, there will be no more armature problems. Next problem area is the condenser. Until the late Thirties, most magnetos were equipped with Mica-insulated condensers, which could last a lifetime. The second world war disrupted supplies of mica from Rhodesia and India, prompting manufacturers to come up with a replacement, a condenser with alternating layers of metal foil and waxed paper. The wax degrades with time and exposure to moisture, and you have a faulty condenser. A correct type of condenser for a magneto must be able to withstand heat, cold, oil and humidity, but the main thing is that it must be able to work with high frequency voltage peaks. Very few modern condensers will survive for a long time in this environment – many Lucas magnetos overhauled in recent years have had a short condenser life – 1-2 years has been normal. Charles M. Falco, an experimental physicist and member of the Antique Motorcycle Club in the U.S., has dug into the condenser problem, and tested a large number of condensers available in the market. His results have been published in the Antique Motorcycle Vol. 50 nos 3 and 4 (2011). To make a long story short, he finally recommends using pairs of Panasonic 0.082 microfarad polypropylene-film capacitors. When soldered together in parallel (by soldering the two leads of the capacitors directly to each other), they produce a 0.16 microfarad condenser that will fit into the available space in the end caps of Lucas and BT-H single and twin-rotating armature magnetos. These condensers are available from Digi-Key Corporation (https://www.digikey.com) under part no. ECQ-P4823JU at reasonable prices (ca. 50 p or 74 cents apiece).
You will often find that the armature is slightly off-center in the magneto case. Sloppy work at the Lucas factory. Likewise, the slip-ring is often not ground correctly (this was regarded as apprentice work at the factory – and quality control was not very good). Dave Lindsley will do a good job recentering the armature and will also be able to regrind the slip-ring or supply a new one – preferrably with the original felt lubricating pads. (At least that was what he did on the magneto of my 1936 Squirrel). I have also used Sean Hawker (https://www.hawkerelectrical.co.uk) in Bristol. He has overhauled 4 magdynos for me – Lucas and Bosch. Both gentlemen will naturally also re-magnetize the magneto for you.
I have great respect for the BTH electronic magneto, and have one on my Vincent Black Shadow, where it functions very well, but if you want to keep your Scott original, I would try a total overhaul of the Lucas Magdyno. The BTH is expensive, and an overhaul of the original, with new, improved secondary windings and condenser, will give a very satisfactory result without ruining you financially.
Deleted UserIt always amazes me how much grief people will put up with before they are prepared to consider a professional rebuild on a mag! I watched a chap last year kick himself into a sweat on what should have been an easy starting bike (Beeza A 10). The lad had tried every adjustment under the sun but to no avail, it was obvious the mag was not performing right.
I have a modern BTH electronic mag on a pre war V twin. It is an excellent piece of tack which adresses the inbuilt design fault that all 50 degree V twin magnetos have. However they don’t come
cheap, and it is probably a bit of a luxury on a road going Scott.
When it comes to chosing someone to rebuild a mag, from bitter experience, I suggest that you find someone local to you, someone to whom you can take it in person.
Many years ago I was recomended to a well-known repairer ( who is still in business) for a rebuild on a veteran Bosch magneto. Anyone can have a problem, but I was less than impressed with his complaint handling procedures and have subsequently heard that I am not the only disatisfied customer for this chap. After posting it back twice, In the end I paid someone else to rewind the (rewound) armature, I had lost all confidence in him. That was the last “mail order” mag I had done.
For many years since, I have taken my custom to Mick at FTW Motorcycles at Sheffield, with no problems whatsoever. Suggest you ask around locally, check with Old Bike Mart etc, to find someone reliable. Believe me, it is worth knowing that if it doesn’t work properly, you can go back and bang on the counter!
Regards
Malc. Webb
Deleted UserI have fitted villiers condencers to B T H mags on 4 b japs and found them to be ultra reliable over many seasons of racing its a bit involved but worth the effort.Regards D F.
Deleted UserMany thanks for all the advice. At the moment I am leaning towards stripping the mag down myself to see if there is anything obvious and then take it from there. If it needs a total refurb then that’s what it will get. What I didn’t want to do was was to pay good money out only to end up with something worse than I started with. It seems to me that there are people out there who don’t have much in the way of quality control.
I’m very grateful for the reliable contacts mentioned and if I need work doing I will be using one of them, I don’t think we have anybody local. The info on condensers is usefull, many thanks.
Tony Kitching
BRIAN MARSHALLHi Tony,
Don’t forget to remove the spark-gap safety screw FIRST….
Brian
Deleted UserThanks Brian,
Tony
Deleted UserThe higher the voltage, the more easily it breaks down suspect insulation. I had a couple of BTH compromise mags rebuilt once by John Cooper, now sadly no longer with us. I had a couple of Scotts with mags rotating in opposite directions. I asked John if he could rebuild them so I could use them in either rotation only by changing the contact breaker. He told me he could do this, but to do so he would have to set the contact breakers so neither were breaking at their optimum flux. He said that although the spark would be of slightly lower voltage, it should work OK. One lasted 5 years racing and the other 6 years racing. I then had them rewound by another rebuilder as John had died and I believe they were wound with extra windings to give extra voltage. Unfortunately, when this is being considered, it should be remembered that the mag on the Scott runs at engine speed and if you are racing and using 5000 rpm, then this is equivalent to expecting the mag on your four stroke to rev reliably at 10000 rpm. One mag lasted 3 laps of Cadwell and the other 5 laps. Do remember that the voltage required to jump a spark plug gap is directly proportional to the gap. If you have a weak mag, the first thing to try is to drop the gap down to about 10 thou. It usually starts much easier and you will be hard pressed to notice any difference in the performance. Of course I take for granted that unless you are a masochist, you are using a decent plug. I never economise on plugs, but then I never compromise on anything if I can avoid it. I use NGK Iridium point plugs BPR5EIX which folks will tell you are soft, but they suit the Scott as it runs unusually cool. Given I have always pushed the boundaries, I made a test rig to check out the accuracy of the mags I had. I could not get a good BTH mag to go beyond 3500 rpm before the cam started floating. Sure there was a spark, but the position started floating about and it became obvious that what I had thought was engine power / gas flow drop off was in fact the spark losing timing. I made my own electronic mag but because of component sizes, I had to run it at twice engine speed. It worked OK and Richard is still using it on his bike. When old racing friend Tony Harris bought the BTH tradename and started to make his electronic mags, I had a prototype. Tony has retired now and the company has a new owner so I can say without any fear of favoritism that I have never had a moments problem with my new type electronic BTH mag. So the golden rule if you want a bike to enjoy is get a good mag, make sure your carb is in good condition with special attention to needle jet and needle (as the jets wear very rapidly) and if you are using a four stroke type silencer, fit a bush in the tailpipe with a 7/8″ bore to give a bit of backpressure. If a customer requires an original mag rebuilt, I send them to Sean Hawker who is a kindred spirit. Same as everything else in life, you get out in proportion to what you put in! Kindest Regards Roger
Deleted UserHi everyone, here’s an update on my magneto.
I could find nothing obviously wrong, so cleaned everything up, stoned the points flat and reassembled it .I set the plug gaps at 15 thou. (as per Roger) and everything is now back in place. With regard to the plugs,I use Champion D16 (18mm) which perform faultlessly. I take them out about twice a year to check them, and usually put them straight back. they come out a lovely brown colour and usually dry. I should explain that although the bike is a 1947, the engine no. is DPY 4613 which I think is 1938. Also the bike runs only on petroil at 30:1 which is the best modification I have made to the bike.
Frustratingly, I can’t try out the bike because after the local boxing day run out, I removed the exhaust pipe and it is now with a local firm who are making a stainless steel one for me. I had bodged up the pipe just to do the run but on the way home it was attracting a lot of attention. However, just kicking the bike over I can see that there is a much stronger spark than I had before and so I wait with trepidation the return of my exhaust pipe.
Thanks to all those who offered advice.
Deleted Usertry an external .25 capacitor mounted externaly connected to the cut out terminal. Easy to do and cheap! often works very well. Cheers Dennis.
