Magneto Timing

[Stuart Lister]

I have finally managed to get my EW running, it is MOT'd and licenced, and completely road legal. I am pleased to report that many of the things I was worried about, like the oil pump, brakes, clutch, gear change etc all work fine.

I have just got one problem. The ignition timing seems to automatically retard itself at a rate of about one degree per mile. By the time I have done fifteen miles, it is so far out that the engine just dies, and it's a long walk home. I have worked out by means of black marker pen dots that it is the conical key on the end of the magneto that is slipping around the shaft. I suspect that the key and the magneto are not properly matched, and the taper fit is only touching in a narrow ring, rather than the whole surface being in contact. Does anybody have any suggestions as to how I should fix this? Should I glue it on, and if so what sort of adhesive should I use? I don't want too permanent a fix, because I may have to pry it off some day. Maybe I could try to drill it and put a grub screw in?  What do you think?

All suggestions gratefully received,

Stuart.

[aggettd]

I have read somewhere that Loctite can be used for just such a purpose. I've never tried it, but it might be worth the attempt. You'll have to decide which colour, but if you are sure of the timing, I'd go with the most tenacious. With the timing self-retarding (I went to school with some fellows who also fit that adjective) you run the risk of overheating the exhaust pipes and ruining the pretty chrome. Minor yellowing can be easily buffed out with "Blue Job". (I didn't name it, I just use it!!)

David A.

[Ian]

Maybe some valve grinding paste and ensure that the tapers are ground in ? Otherwise there are a couple of loctite products that would work - can't recall the number but I am sure there is a shaft seal and there is the retaining compound 641. May need heat to remove though.

[Doug]

Lapping the taper to a good fit would be the best course. Oscillate the gear back and forth through 90 degrees a few strokes, pull off frequently, and place back on a further 90 degrees and repeat. The point is not to stay in one place overly long. Also pulling off and replacing helps stop all the lapping compound working out to the ends, but you should still re-distribute it often with your finger. Also do not press too hard, you will just squeeze the lapping compound out of the tightest spot, where you want it doing the most work. A light twirl and move on is best.

Most all Loctite grades can be broken at just over 400F, so a propane torch to the hub of the gear to warm it up does the trick without roasting the magneto. Yes there are many grades. It should not take much to keep it in place, the magneto does require a phenomenal amount of torque to drive, less so as the magnet gets tired. So one of the field removable 'nut lock' grades would do. Bearing mount would be a stronger grade. Hydraulic sealant would likely be too thin if you do not lap and the fit is not that great (gap at one end.) So one of the more viscous grades would be the choice. Loctite also does a 'liquid metal' product for fixing broken out key seats. Not sure how good it is, but would probably work for light duty. If you lap the taper properly, you should not need to use Loctite at all. Loctite does have a website (of course) listing all the various grades, uses, and product numbers (which they change every few years just to confuse everyone, hence my not quoting any numbers!) Their home page is: http://www.loctite.com/int_henkel/loctite/entry.cfm

-Doug

[Stuart Lister]

Thank you all for your help. I did not reply immediately because I wanted to make sure I had fixed it before I got back to you.

I lapped the taper in with grinding paste exactly as you suggested, and both surfaces turned a nice uniform dull grey colour, so the paste had obviously done it's work over the entire surface, which was reassuring. I then used a medium strength loctite, and when I came to check it, of course, the timing was out! This was not such a bad thing, because it gave me the chance to find out how difficult it is to dislodge a taper bonded in place. actually, it wasn't too bad. A screwdriver wedged in place behind the key just needed a sharp tap, and the key flew off. After cleaning the residue off, I managed to time it right on the second go, and the problem is sorted. I have done a number of short runs and the timing is still spot on. Thanks again for your help.  Stuart.

[Clive]

Hi Stuart,
Just as a matter of interest which ignition criteria did you use the early one 50 degrees fully advanced or the later one - 5/16 btdc revised to 15/64 btdc this timing was quoted mainly for the later EW with detachable heads . Over the years i have tried different timing on my fixed head motor and to be quite honest not much difference has been noted . As the timing is constantly being altered for different road conditions full advance is only used for light running down hill and a following wind ,grades are climbed using progressive amounts of retard as the engine slows doesn't take much to slow an EW .
Regards
Clive

[Stuart Lister]

Hi Clive,

The Data sheet sent to me by the LDMCC says the timing should be 45 to 50 degrees before tdc, so I made my mark on the flywheel at 47 degrees. Sometimes it's very useful having an external flywheel isn't it?

Your comments about the advance retard lever are interesting. Mine is spring loaded to the fully advanced position (slack wire is fully advanced), so I have just been using it to start the engine (I don't know why I bother cos the engine starts just as easily without!), and after that, I have been running on full advance all the time. Is this wrong? should I be using the A/R lever to tune the engine on the fly? I seem to remember reading somewhere that modern fuel is much more stable than the stuff that was available decades ago, so advance/retard adjustments were less beneficial, but perhaps I've been overlooking something important. What do you think?

Stuart.

[trevorp]

Fuel burns at a fixed rate so the faster your engine goes the earlier u have to light the spark hence most bike and cars advance timing as engine speed increases by a mechanical advance or spring loaded affair
When i say it burns at a fixed rate this means at the right mixture as a rich mixture can burn slow because not enough air to burn quickly and a lean mixture will burn slowly as well as it has a longer flame path to jump across the fuel molecules
The reason most cars had a vacuum advance was at high rpm with slight throttle it is a lean mixture so it needed to be advanced even earlier
Hence cruising on light throttle requires more advance than normal
To much advance causes pinging if anyone has heard it just remember the ping sound is your conrod being compressed a bit like hitting it with a hammer which causes piston conrod and big end failure
As a general rule of thumb if your engine pings under severe load eg up hill at full throttle u must retard the timing until it just stops this would now be the ideal timing This is a rough way of timing a car or bike without any equipment

[Clive]

Hi Stuart ,
Unless your EW is very different  the magneto is fully advance with the control wire fully tight the normal magnetos are spring loaded fully retard check again and let us know
Regards
Clive

[Stuart Lister]

Hi Clive,

Oh, I hadn't thought of that. All my previous experience has been with post-war machines where the magnetos have been fully advanced with the wire slack (presumably in case the cable breaks, it may be harder to start, but it'll get you home!), so I'm afraid I took it for granted that this one would be the same. Perhaps it isn't? Maybe I've been timing on full retard?

The magneto is a BTH type M2-W2 which I believe is original. I am away from home at the moment, so I won't be able to check it for a couple of weeks, but I'll let you know.

Stuart.

[Chris]

With the earlier machines, it is possible to have twin cylinder magnetos (EIC, Thompson Bennett and others) that run clockwise or anti-clockwise depending upon the machine/model for which they were originally provided. With the rarity of good early magnetos it is not practical to be too picky about this and it is possible to change the direction of rotation which can be done when at least the contact breaker assembly should be changed. However, the result of using an incorrect rotation magneto means that the full advance can be a slack wire. In respect of BTH mags as used on EW, I do not know whether these were available with a choice of rotation.  Chris.

[Stuart Lister]

Thanks for that Chris.  I don't know the history of the mag, so I can't guess at it's originality, but the direction of rotation is stamped (correctly) on the brass plate on the end, so I don't think it has been altered. Like I say I can't check for sure until I get home.

Stuart.