Another JM magneto resurrected

[Hugz]

I adapted a Mk1 coil into a JM magneto with excellent results. Interestingly at first I couldn't get a spark yet when I hung onto the lead.... ouch. Pulled the points apart and cleaned and all good. I'm a little concerned how close the screw heads are to the brass lid. Worth insulating? I even had the plug set at 60 thou and the spark had no trouble jumping across. Probably need to have a photographic illustration where the fibrous insulated washers go on the stud points set up. Are the photos on this forum secure now? It is all a bit fiddly. I used a couple of old bolts ground down to make a 9/16" to 7/16" sleeve. Would be easier if I had 9/16" round rod and just cut to length and drill a 7/16" inner hole to take the more common 7/16" coil cores. I'll keep an eye out. Ok, 2 more to go and then I will have 6 JM magnetos working. I'm short one flywheel but that is ok as a base plate will be with me as a spare on a boat. Fleetingcontact you might recognise this plate. Love the way it is so easy to use a puller to remove flywheel on JM coolie hat magnetos. I do think Seagull went backwoods going to the MK1 on am I biased..... Not very happy belting flywheel nut to remove, hardly gentlemanly behavior.

Had to follow the instructions here
https://www.youtube.com/watch?v=a0k5tFWHEtc

[Hugz]

Has anyone a source for the 2BA long, round head slotted set screws that go through the JM coil support and hold the HT lead spring on the underside? About 1.3/4" long or 45.5mm. I need a couple of dozen and matching brass nuts. Thanks.

[Charles uk]

I think John Williams has some.

[Oyster 49]

If John does not have them try George at Villiers parts.

[Hugz]

I thought I would table the sequence of the screws/insulator washers in the studs point boxes. There are four washers. Two that are solid that fit on the base of the points box and two that are stepped that the wires from the coil and condensor wrap around to insulate from the screws. There is also a rubber grommet on the side of the box where the wire from the coil comes through. There is potential for a breakdown of insulation at the side grommet position and the fibrous washers. So far these fibrous washers seem to to be standing up to their age well. Try not to over tighten securing screws. Previously I was concerned the screw heads were too close to the lid but they are of the same potential so no problem there. It is easy enough to dissemble and clean points. From the base up.... solid fibrous washer.... points bridge..... stepped fibrous washer with wire around inner step.... screw all the way through. Fun!

[fleetingcontact]

Just read this post, loving your work. I'd seen your earlier video on coil replacements so |I knew that stator would be in good hands. I simply don't have the patience, although I'll be attempting to prise apart a Villiers magneto soon and if successful it may well find its way onto a lowly SJP I'm playing with. What's your advice on freeing all those tiny stuck and inevitably well-rusted nuts and screws?

[Hugz]

The usual, penetrating oil, heat (not near the coil though) and the mighty manual impact driver. On the mk1 use double nuts to bind onto stud to unscrew cheek studs. I did have one screw on the JM magneto that didn't wish to move. I had to grind down from the back of the plate (was only proud 1mm) and take down a little below the surface including the surface of the plate (which left enough threaded meat to reinstall). Enough of the corrosion was gone to enable removal of screw. The studs on the back of the round points block can be gripped with side cutters close to the back of the box (after the box has been removed). This part of the thread is not used as it is where it goes through the plate so any damage irrelevant. I think having a good size vice that has large enough jaws to take the magneto plate horizontally makes a huge difference. I also grind the impact driver bits to be a good fit into the slotted screws (mk1). I'm an Electrical fitter/mechanic by trade so feel quite at home playing with these. Good luck.

[fleetingcontact]

Thanks for that Hugz, I'm sure will be useful when I get into it. Was it co-incidence that I recently made a magneto test thingy the other day? It was supposed to be for testing Mk4 CDI but could just as easily be used for trying to energise Villiers coils etc. Hadn't thought of your spark-plug accessory though, now done. So the plan is that I'll try and see if it gives a spark first. Then test for continuity...but if, as expected, the coil fails both these tests then this at least gives me more of a licence to apply violence! I have two other candidates (which I expect will be just as o/s as the first). Still, you never know.

I've saved some pics and destructions from an earlier post on how to test a coil for continuity - if any of you want to see them let me know but its all out there already. Any pointers on how to test the condenser?

Martin.

[Charles uk]

There is no electrical reason why a Villiers coils would re-energise after spinning, other than the low voltage arcing at the points would erode some of the filth that "clean & set the points twice" should have done, if the job had been done properly the first time!

My favoured Seagull ignitions for just about all of my use are the Wypac Mk3 & Mk4 CDI's, a very strong spark even at silly compression & stupid revs & they start real easy, even with their low inertia flywheel!

Whatever you do Don't mix the flywheels!

Don't give up on that Mk4, John has some new ones, & it's very rare for them to go intermittent as in my experience they seem to be dead or alive!

[fleetingcontact]

Not giving up on MK4 CDIs, but I want to test the eight or so spare units I have, which it seems can only be done dynamically. As you say, it either works or it doesn't - I have never known any electronic ignition system to be any different. If you know of a better test then do tell us. So a spark at the plug using Hugo's mod seems good to me, better than the youtube video of a test done in the dark and observing the bare end of the HT lead - a good ground should protect the unit. It does introduce more variables though, inasmuch as the plug or plug-cap. By the way, do you have any experience changing HT leads on MK4s?

At the moment an SJP I have has a Mk2 mag but the MK1 was horriginal. I lately bought some scrap metal which contained amongst other things a MK1. I'm just messing with it because I have no experience of them and for, like, fun. If I can get it all to disassemble then I might go all the way and buy a new coil but my expectation is that it will be past redemption. Hugo would clearly disagree.

Thus the question about condensers - this great thread seems to have covered all other aspects of magnetos with Villiers coils.

[Charles uk]

You can change the HT lead on a Mk3 but not the Mk4, I've extended them with screw in 4mm connectors but finding 4mm copper cored is difficult.

I test mine on the motor they're fitted to, if dead I replace them.

I've seen Seagull's own test rig it had a 1/4" gap, all ignitions I was told had to jump that.

It will take a couple of weeks to get a picture, if it hasn't been binned.

As most of the late model ones I build are for racing, I tend to use all new components as it's a lot less work to blueprint.

My test rig was as described.

Does the Mk1 have a 9/16" or a 7/16" core?

[fleetingcontact]

Not being up to speed on these things I am assuming you mean the lugs at either end of the coil which I have just measured as .4385 which on handy-dandy conversion table gives the actual fraction as .4375 or 7/16"

[Hugz]

I've decided to dress the end of my horseshoe laminated coil mounts on the JM magneto plates. I wish to be in a situation where I can swap plates and flywheels around. The tolerance between the flywheel magnet and the coil mounts are very fine. Being made of thin laminated iron make them somewhat fragile and prone to distortion. Where the flywheel might rotate free before the replacement of coil, after maybe a different matter. Basically I inked the ends of the horseshoe (I used a texture pen) and rotated the flywheel to see where it was scraping. I then dressed with a file. Didn't need much. Mk1's have a good clearance so no concerns there.

Only top half need dressing.

The whole face needs dressing.

[Hugz]

Interesting that with all the changing of flywheels I burred the woodruff key and the flywheel wouldn't slide down. It was a very small burr on the top. I just needed to run it up and down some emery paper. They are quite soft.... are they sacrificial?

I get a bit lost with the condensors too. I've yet to have one fail. I put a 12 battery charger across the - earth (metal bit) and the + lead for 10 seconds then remove. I then measure with dc volts on my multimeter and get a very quick deflection of the needle as it discharges. You can test it in situ too. Put a bit of paper etc between the points and desolder the wire to the coil. Negative to anywhere metal on the base plate and + onto the terminal on the points block, hold for 10 seconds then remove. Measure with multimeter on DC voltage and watch for needle deflection. A six or 12v battery would probably work. If you have a farad range on your meter it would be easier I would imagine.

[fleetingcontact]

Great info. I have three points boxes not including the newcomer so I'll have a go with that. I also have two 6v batteries. Is 6v better than 12v in this case? I will look for this 'farad' range of which you speak but bear in mind I recently looked up a web page titled 'How to Use a Multimeter'... why is a farad range preferable?

In the meantime I searched for earlier threads on the subject. The consensus is less encouraging than your perspective; the summary is that testing condensers is complicated and a bit academic because the results are unreliable...as is testing a coil, or a HT lead...doh. But, on the positive side and like your experience, other users report that the part has never failed.

Thanks once more.