K2F magneto without advance and retard

[Dan Kristiansen]

Hi,

I recently bought a 1955 G9 in bits.
The magneto i have is a Lucas K2F, But there is no manual or automatic advance or retard. The timing is fixed / static.
The magneto gives a good spark but I'm guessing this isn't correct for the bike?

Thanks.

[Groily]

Not correct for the bike, no.
The correct Lucas part # would be magneto K2F 42230B/D, with manual camring.

If yours still has an ID label on it, you can compare the numbers!
You've got one for a Beesa/Trihard/Notrun etc, with a fixed camring for an Auto Timing Device, with which the AMC twins weren't equipped. (And which it is very difficult to engineer for a variety of reasons.)

It is possible to modify yours by obtaining a camring housing for an advance and retard cable if you can find one, then notching the camring to provide the necessary arc of movement, plus a slot for the plunger for operating it . . . but it would require extracting the bearing outer race from yours and fitting it into the replacement, and probably re-shimming the endfloat of the armature, on top of the kerfuffle with a dremel or similar grinding weapon. Better to find (swap for?) the right item if you can, especially if you want to retain the elegant alloy dome points cover and so on, with which most K2F versions were not blessed.

That said, a G9 is pretty soft and will behave not badly on fixed timing (I've run like that over the years on my 500s, also 650s) . . . but it's not for everyone, certainly!

[Dan Kristiansen]

Hi Groily,

Thanks for your reply.
Given the costs involved I'm tempted to convert my magneto housing into electronic ignition.

I have seen that the static setting is given in a linear measurement from TDC, Do you know the angular settings?
I will set the timing with a strobe but wanted a good base setting.

Thanks.

[Dan Kristiansen]

Also, If I was to keep the fixed timing, What setting would you recommend?

Thanks.

[Groily]

Not quite sure what the figure in degrees is to be honest for the 500s. But it's 'high thirties' from memory. I tend to go 35 or 36° to compensate a bit for modern fuel, and things seems fine. Most of our sorts of machines seem to do well on a couple of degrees less than 'book' these days. Others may have a slightly different take on it though - I don't think there's 'right' and 'wrong' any more. Fuel comes into it too - I use 98 octane E5, as it's the best we can get here. I run my Model 31 at 35°, fixed timing, with no problems.

With electronic systems, the advance figure may not be the one used for initial setting up, and the advance / retard range may not be the same as that offered by a manual magneto, but if using a strobe I'd aim at 36° by about 3000rpm. Then, as ever, trial and error until you're happy.
(The Thorspark system uses the same manual advance as the magneto, so the range is the same I guess. I have only ever had Boyer systems myself on the electronic side, and I left their mysteries undisturbed as much as possible!)

[Dan Kristiansen]

Thanks for the information.
From what i have read the boyer system could be the one to go for.
I assume it has an advance curve built in, i cant find much technical information on that side of things.

Im sure you are correct with the 35 degree BTDC it just seems excessive on start up.

As you say, trial and error.

Thanks.

[SPRIDDLER]

I'm sure you are correct with the 35 degree BTDC it just seems excessive on start up.

Shouldn't be a problem as on start-up you're only kicking over 249cc at a time.

[Groily]

Thanks for the information.
From what i have read the boyer system could be the one to go for.
I assume it has an advance curve built in, i cant find much technical information on that side of things.

Im sure you are correct with the 35 degree BTDC it just seems excessive on start up.

As you say, trial and error.

Thanks.

The Boyer systems are OK, but the ones I had some years ago (labelled Norton) needed a fully charged battery to start the engines, and used a fair bit of current. They were on alternator machines from the '60s, one Norton, one big Oilfield, not dynamo bikes for which I think things could be marginal - and where you'd need to go 12v if not already I think.
The current requirement would worry me on any dynamo bike (unless the latest versions are less demanding). An Alton alternator might be an option of course.

The advance curve is built in, yes, on them. The Thorspark is the least demanding and I've seen a few of them working really well. But some folk - including some on here - haven't got on too well with it. Pazon are also rated highly by some people and probably worth a look . . .

Starting with fixed timing does need a solid swing, no deviation or hesitation, that's for sure. Luckily, I am, er, of a somewhat solid composition, and have no problems. With a manual mag and about 18° of A/R movement - 36° on the crankshaft - you're at high teens / low twenties° BTDC at say half to one third retarded, and it's certainly a better place to be. As Spriddler is too polite to say, Twins are a bit Girlie really, from the starting point of view!

The reason I like fixed cam mags is because they suffer less fretting between camring and housing, maintain their firing interval better, and there's no plunger to get jammed, cable to break, nor that awkward routing around the carburettor, where things are uncomfortably tight in my view unless you move the cable adjuster to mid-point. The other thing is that the spark is at its strongest at full advance.

Ideally, an ATD would be good, but as I said, hard to contrive on AMC twins. I did fabricate one, using a spare camshaft pinion and the typical Lucas ATD guts as found on innumerable Beesas etc, but it was a lot of nadgery work to get things into the space on an engine with the narrow timing cover (not the fatter later one for larger oil pumps).

Personally, just my own bias and all that, I reckon your hard-earned would be well-invested in a magneto overhaul, but it's a fine balance and I'm not one-eyed. As time passes it's going to be harder and harder to get mags sorted, as it's not a career choice for people who've grown up with clean hands and screens to stare at. Which is sad, I think.

[SPRIDDLER]

The Boyer systems are OK, but the ones I had some years ago (labelled Norton) needed a fully charged battery to start the engines, and used a fair bit of current.

I've never had electronic ignition, only magnetos, but I agree as I'd also be anxious if it relied upon the E3LO dynamo for battery charging at 6v or uprated to 12v by regulation only, since at 12v the revs need to be kept well up to maintain 12v output. I recall a post where the owner had starting problems as his battery was too low to cause the Boyer (or Pazon?) system to go to the retarded state from it's default fully advanced condition.

As Spriddler is too polite to say, Twins are a bit Girlie really, from the starting point of view!

Luckily, I am, er, of a somewhat solid composition, and have no problems.

I was also too polite to mention that.

I must admit to being twin-averse as I've only had or ridden one; a 15 quid Excelsior Talisman twin that I bought in 1962 with four weeks apprentice mechanic's wages. It took me a month to get it going and on the first (and only) ride it spat out a sparkling plug two miles from home. I abandoned it in the front garden of an old peoples' home from where a pal bought it for £7 two weeks later.

[Groily]

I've never had electronic ignition, only magnetos, but I agree as I'd also be anxious if it relied upon the E3LO dynamo for battery charging at 6v or uprated to 12v by regulation only, since at 12v the revs need to be kept well up to maintain 12v output. I recall a post where the owner had starting problems as his battery was too low to cause the Boyer (or Pazon?) system to go to the retarded state from it's default fully advanced condition.

Yup - there's the rub. And even if going for the full 12v conversion with fine windings to keep voltage up at low rpm, you're going to struggle. There are just 5 amps available, and the BB ignition will swallow about 2 of them on average, leaving precious little for other things. LEDs would be a must for illuminations.

Luckily, I am, er, of a somewhat solid composition, and have no problems.

I was also too polite to mention that.

That's OK Spriddler. We larger people can take it! And dish it out to persons of restricted growth if pressed!

I must admit to being twin-averse as I've only had or ridden one; a 15 quid Excelsior Talisman twin that I bought in 1962 with four weeks apprentice mechanic's wages. It took me a month to get it going and on the first (and only) ride it spat out a sparkling plug two miles from home. I abandoned it in the front garden of an old peoples' home from where a pal bought it for £7 two weeks later.

THAT'S not a Twin - it's a chainsaw with wheels!!!