Iron 4G Coil Ignition Conversion.

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Iron 4G Coil Ignition Conversion.

Postby John.reader » Tue Aug 25, 2020 11:19 am

There is a previous thread on this forum on this subject, but although its headed coil conversion, its mainly about Solex carburettor problems, so I thought I would start a new thread.

I am building a 1937 iron square, and having read a great deal on this forum and elsewhere about the failings of the Lucas 4G magneto, especially when hot, that I thought I would explore any alternatives. Electronic ignition kits don’t seem to be available any more, but I found a short article in an old Ariel Square Forum booklet about a simple conversion to coil ignition using the points in the original magneto. I believe that Paul mentioned this in the previous thread, and at least one other person was asking about it, so I have attached a scan of the article if anyone wanted to read it. I hope I’m not infringing anyone’s copyright by doing this.

The whole thing seems elegantly simple to me and I cannot see any reason why it wouldn’t work, although I do have a couple of queries. The low tension current passes through two moving carbon contacts on its way to earth, and any intermittent contact here would produce sparks at all the wrong times, and also because of the extra load on the battery from continually feeding the coil ignition the dynamo would have to work that much harder, putting an extra load on the fragile and semi non replaceable fibre drive gear.

Also, if I was to go this route, should I remove the armature coil windings completely, in order to prevent any problems with shellac, or would the weight of the windings act as a flywheel to smooth out the revolutions of the armature shaft and help extend the life of the fibre drive gear.

Other than that I can’t really see any problems with it. Does anyone else use this system, and if so how have they been getting on with it.

Alternatively does anyone know of any other conversions that may be available. I seem to remember reading many years ago about a conversion kit that replaced the magneto armature with a plain shaft with a cam on the end of it, and a metal plate with a fixed set of points on it that fitted in the end of the magneto. However I cannot find any information about it now.

As before, any information would be much appreciated.

John.
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paul.jameson
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Re: Iron 4G Coil Ignition Conversion.

Postby paul.jameson » Wed Aug 26, 2020 10:51 pm

My short answer to this question is that I would recommend sending your magneto to Tony Cooper for rebuilding with a request that he should fit the later end plate, assuming he has one available.

The long answer starts with me buying my first Square Four, a 1948 4G. and putting it on the road in 1988. Although I persuaded the magneto to spark reliably, long trips showed the familiar problem of misfiring once the magneto got fully hot. The problem was mitigated somewhat by a spate of rear wheel punctures (another story) but sitting at the roadside changing inner tubes did allow the magneto to cool down and spark properly once more. Having bought a copy of Square Forum, I converted to coil ignition according to the instructions. To my surprise, the misfiring when hot problem continued. The problem was fully documented in Cheval of June 1990 - Page 20 - available on the website now , courtesy of the excellent efforts of Pete Collins - thank you Pete. Although several issues are listed in that article, the major one is that unless you isolate the magneto condenser, it will remain in circuit and if defective (which they usually are) will continue to give the misfiring problem after you have converted to coil and fitted a (good) external condenser.

Although I haven't tried it lately, I think the only way to isolate the magneto condenser involves removing it from the armature which in turn requires removal of the armature windings. This seemed like a good idea anyway, to avoid the problems of jamming due to melted shellac and provides the opportunity to use the old HT pickup as a second pickup from the points to the coil by fitting a wire between the old slip ring and the centre contact on the points plate. I used for this purpose a length of the thick primary winding copper wire which I had stripped from the armature. In time, this proved a poor choice.

By 1991, the Square was performing well and reliably, to the extent that I was able to complete my first London - Edinburgh run on it (with sidecar) that year. It continued to perform well and reliably for a further couple of years until I rebuilt it in 1994/5 and fitted a different sidecar. This time, I used a small battery on the bike instead of a large one in the sidecar boot. The bike had been on 12 volt electrics ever since the coil conversion.

In Spring 1997, I managed to get my 1936 OHC Four on the road. As it had the same magneto (apparently) as the 1948 Square, I fitted the coil conversion (and 12 volt electrics) straight away. I had multiple problems of misfiring. Eventually, I came to the conclusion that the high revving OHC four simply got the points (which run at engine speed on a Square so at twice the speed of (say a Triumph) twin) to the stage when they would not open and close correctly at moderate revs and above. This tied in with advice from none other than Titch Allen who told me that after about 10,000 miles the only thing to do with a Square Four magneto was to mend it with a new one. This was his experience from the time they were made. A huge amount of careful changes of cam rings and points plates got me to the stage where the bike was useable and I took it up the western isles of Scotland with the late Bob Brassington and two other Ariel riders in September 1997. Roland Robinson had warned me of the tendency of the OHC fours to strip the fibre gear wheel driving the dynamo and distributor so I took a spare with me. By the time we got on the ferry to Arran, my bike was rattling badly. By Mull it was worse. By Skye it was worse still and there the fibre gear stripped. So I fitted the (brand new) replacement. It lasted less than a day so I had to be recovered home. The rattle proved to be the coupling gears loose on the crankshafts and I am sure that it was the pulsation effect of this fault which caused the fibre gears to be destroyed.

A re-think was called for, once I had rebuilt the engine. The upshot was a conversion to Newtronic electronic ignition which solved the misfiring problem completely and led to much better flexibility of the engine. Basically, it took it back to the sort of flexible performance which the reporters raved about when the OHC four came out. Although basically a Newtronic system, I used a disc to "chop" the light beam of the electronic unit which was made specially for the purpose by the then Square Four Spares Organiser, David Jones. The system was so successful that it was available through Draganfly for a time - until Newtronic went bust.

Probably about 1998, Len Ore organised the first of the Forest of Dean Crazy Horse rallies in early January. I booked in and took the 4G and sidecar. En route, the bike started to misfire at anything above very moderate revs. I decided against trying to solve the problem at the rally and limped, increasingly slowly, home where the 4G and sidecar were slung in the shed in disgrace. Inevitably, to cure the misfire, I decided to fit one of the Newtronic electronic ignition systems. Whilst doing so, I found that the cause of the misfire was that the copper wire I had fitted between points end and slip ring on the armature had fractured, presumably due to fatigue over time. As the armature rotated, the broken ends of the wire were flung outward to short out on the inside of the magneto casing - a perfect governor mechanism (if I had wanted one.)

Converting the 4G to electronic ignition did not give any significant improvement in flexibility or smoothness as it had done with the OHC four. I put this down to the lower revving nature of the 4G. But the misfiring had gone for good.

When the OHC four stripped another fibre gear for no apparent reason, I realised that its magneto used a narrower fibre gear than the 4G one had. In fact, the 4G fibre gear is a third wider again that the OHC Four one was. The difference in width is accommodated within a different end plate / distributor base on the magneto. The end plate for the wider gear is fundamentally flat on the outside whereas the end plate for the narrower gear has a ridge up the centre. The dynamo drive gears vary in width correspondingly, but otherwise, the parts are interchangeable. I am certain that the narrower gears were used in 1936 on the OHC models, in 1937 and possibly 1938 on the 4G models and in 1939 on the 600cc pushrod models. Going for the wider gear makes all the sense in the world given that failure of the gear leads to loss of the distributor and therefore, almost certainly, a call for the recovery people. If you PM me a photo of your end plate I can tell you whether it is for narrow or wide gears. I use a wide gear system on my present 1936 4G, for obvious reasons.

So with the misfiring sorted, was that the end of the problems with the coil ignition system? Sadly, no. The 4G, especially with sidecar, developed a habit of the charging system failing. The dynamo was the problem and eventually I found that the solder between the armature windings and the commutator was melting and being flung off. I tried high temperature solder, a brand new old stock armature and even rivetting the wires in place but the lack of charge, or reduction in charge, happened whenever I used the headlight for any length of time, with or without sidecar. Fundamentally, the electronic (or coil) ignition was demanding more from the dynamo (even at 12 volts) than it could supply without overheating and melting then flinging the armature solder. I never did solve that problem because I sold the 4G to buy my first Healey. Perhaps you could reduce the load on the dynamo sufficiently by use of modern LED bulbs, particularly in the tail, speedo side and panel lights. From what I have heard, if you want to see where you are going, LED headlamp bulbs are not the answer. For the time being though, my 1936 4G works well on a Tony Cooper reconditioned magneto, wide gears, 12 volt electrics with electronic regulator and conventional bulbs.

Feel free to ring me on the number in Cheval to discuss if you want to. We don't live too far away from each other if you want to come and look at the 4G.

Paul

P.S. I had planned to take the 4G to Germany and Holland in 2018 but a fractured pannier bracket led to a return home for the KH which did the trip with the furthest traveled award as a result. I was concerned about the possibilities of stripping the fibre gears en route and the difficulties of replacing the fibre gear by the roadside so I had a discussion with Tony Cooper. The only way to remove the fibre gear is to press it off with the magneto dismantled. But there are 3 holes in the steel base of the fibre gear which could be threaded (say 4BA) which would enable removal and replacement of the gear at the roadside (provided you carry 3 No 4BA allen bolts or similar). I will tap the steel base of my fibre gear accordingly next time I take it off but I did have the tap and allen bolts with me when I set off for Germany, along with a couple of spare fibre drive gears.

P.P.S I do have in stock one NOS Newtronic conversion system, just in case.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: Iron 4G Coil Ignition Conversion.

Postby paul_turner » Thu Aug 27, 2020 8:02 pm

An interesting and timely post Paul as I have the 35 cammy on the bench ! previous owner has done that very conversion mentioned in Square Forum and im currently working my way through it and was contemplating ditching it and taking the mag up to Tony to revert back to original ?

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Re: Iron 4G Coil Ignition Conversion.

Postby John.reader » Fri Aug 28, 2020 12:37 pm

Hello Paul, and thank you for your amazingly comprehensive reply. Having read it through in detail several times, plus also reading your article in the Cheval, I think that the best thing for me to do is to go with your short answer and get Tony Cooper to rebuild the magneto for me.

Hopefully without the continual load of the coil ignition, and without the lights on, the load on the dynamo would end up being minimal, so the fibre gear might last a bit longer. Just from reading your post it seems that you have a good supply of them. If its not a secret, please could you tell me where I could get one from as I can’t find them anywhere and it would be nice to have a spare. I have the wide gears in my magneto, the gear is 1/2 inch wide, and the distributor end plate is flat on the outside and recessed on the inside to take the wider gear.

I’m just about to fit the engine sprocket, and I have a choice of 24 teeth with the old three lobe cam or 26 teeth with the later two lobe cam. I was intending to go for the 26 tooth as bearing in mind the problems with the dynamo and fibre gear I thought that less RPM at any given road speed would be better. I know that the engine would easily pull the higher gearing as I also have a 1951 MK1 with a Steib S350 sidecar attached, and that romps away with a 26 tooth engine sprocket. The only problem with this arrangement is that the crankshaft has a small amount of wear on the splines, which might allow the sleeve to move backwards and forwards as the load reverses and thus might break the split pin and unscrew the nut. Obviously this won’t happen with the earlier 24 tooth arrangement which runs directly on the crankshaft and the nuts are done up tight against the crankshaft shoulder. Hopefully plenty of Loctite on the threads might stop this from happening. So which one to choose, decisions decisions.

Before I fit the magneto to the engine I will certainly tap the three holes in the fibre gear as you have suggested so that I can hopefully get it off the shaft without dismantling the whole thing if the gear should fail. I have two of these magnetos, but only one fibre gear. I presume that the missing gear has already failed in the past and been discarded by a previous owner.

Thank you once again for the enormous amount of help that you have given me, you have certainly given me food for thought.

Kind regards,

John.

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Re: Iron 4G Coil Ignition Conversion.

Postby paul.jameson » Fri Aug 28, 2020 9:10 pm

My current 1936 4G has now done around 2650 miles without any complaints in the magneto or dynamo department. I hope and expect it will do many more before the fibre gear fails.

I have 2 or 3 spares, some of which are the narrow type but which will work on a wide type magneto if necessary. One of my narrow spares got Lester Grant back home from France one year when he stripped the gear on his 1946 4G. That, incidentally, is the only instance I know of the wide gear stripping on a 4G.

Where did I get the gears? At autojumbles, on stalls selling Lucas magneto bits. Look at it from the stallholder's point of view. The gears don't fit many bikes so tend to sell very slowly and appear on the stall year in, year out. Just watch you don't buy the larger diameter ones which (presumably) fit a standard type magneto before they devised the slipping clutch arrangement. I would be surprised if Tony Cooper didn't have a few spare fibre gears in his stocks.

I should have told you my system for removing the nut which holds the fibre gear in place. I have a spare (singles) magneto sprocket on which I have filed 2 flats so that you can hold it from turning with an adjustable spanner. I put this onto the magneto shaft and tighten it up which allows me to hold the shaft stationary so I can undo the nut. Then I remove the sprocket using the usual extractor. Re-assembly is the reverse of dismantling, as per all the best instruction manuals.

If you have a 1937 4G with a 1937 rear crankshaft you are going to have significant problems drilling a hole to take the split pin for the 2 lobe cam arrangement. The pre-war crankshafts have a surface which is incredibly hard. I am 90% certain that I used 2 locking nuts, as per the singles, on my crank to overcome this problem, presumably with the locking washer between them and probably with some threadlock for good measure. My inclination would be to use the 2 lobe cam but I have had the split pin / nut arrangement fail on this on my 1948 4G. The shock absorber assembly exited through the primary chaincase and the spring overtook me down the road. It was the only part which I managed to find despite walking up and down the road for well over an hour whilst waiting for the recovery truck to arrive. So quite what / which failed, I don't know.

Paul
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: Iron 4G Coil Ignition Conversion.

Postby John.reader » Sun Aug 30, 2020 11:05 am

Hello again Paul. Thank you once again for your reply, I promise to try and not take up any more of your time.

I have two of these magnetos and parts of a third, but only one fibre gear, the others presumably have failed in the past and been discarded. As I was only intending to use this machine for local rides rather than long distances, hopefully the one surviving gear will last for a while, at least until I can find a spare. The only thing that might shorten its life is that all three of the steel dynamo gears that I have are rusty, two badly and one less so. I have cleaned up the best one and was going to use that, it cleaned up quite well so fingers crossed it won’t wear out the fibre gear.

Your idea for holding the magneto shaft is great. I was trying to do the same thing by wrapping a piece of old timing chain around the sprocket and holding it with a mole wrench. It worked OK but your idea is better.

The rear crankshaft in the engine is from a Mk1 and it has a full thread and the split pin hole in it already. I originally was hoping to use the original pre war crank, but although the thread on the end looked superficially OK it was very rusty, and after cleaning up, when you put a either a new nut or an original nut on the thread it wobbled about and was obviously only touching on the tips of the threads. I thought that as the threads were only touching on the tips the combined pressure of the cush drive spring plus the tightening torque would pull the threads through the nut, and when I had a trial assembly, that’s exactly what happened. When I measured the diameter across the threads it was .020 smaller than the diameter of the threads on the Mk1 shaft that I was going to use instead. A new nut on the thread of the Mk1 shaft runs up and down nicely without any trace of wobble so this should be OK. There is a small amount of spline wear on this shaft so I have fitted the sleeve to the shaft with a small amount of red Loctite on the last half inch of the sleeve, twisted it in the drive direction and have done the nut up. I’ll fit the rest of the parts tomorrow. I only put a small amount of Loctite on in case I want to get it apart in the future, and I’m hoping that this will help prevent the sleeve from rotating as the drive goes on and off.

Today I made a tool to compress the spring so that I could assemble the components without having to fight against the spring pressure, and I put it all together with blue Loctite on the nut. I tightened the nut to 70 lbs/ft which is the same as I used on the other three crankshaft nuts, and when tight I could see half of the split pin hole so it only needed a tiny bit more to get the pin in. Hopefully this will be OK and it will stay together. I hope so as I don’t have any spare outer primary chain cases.

Once again, many thanks again for all your help and advice.

Kind regards, John.

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Re: Iron 4G Coil Ignition Conversion.

Postby Akumar » Tue Sep 08, 2020 8:18 pm

Hi Paul (Jameson),

I sent you a PM regardign Newtronic system.

Kumar
48 SQ4 (with 1937 engine), 43 NG, 51 NH, 53 VB, 58 Colt

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Re: Iron 4G Coil Ignition Conversion.

Postby john.whiting » Wed Sep 09, 2020 1:23 am

I f you want to run coil ignition type current loads through the mag,I suggest you make the brushes from a copper/graphite material more suitable than the carbon used in the magneto ignition......These are everywhere from power tools ,starter motors etc ,and just need to be trimmed to size......If using the points as a trigger only ,then I think the carbon brushes will be OK ,providing the resistance doesnt upset the system..........and as mentioned ,remove any old capacitors from the circuit....With a conventional points system ,you will need a capacitor somewhere ,but it can be on the coil,and hidden under the tank.


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