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Joe Hunt Mag

3K views 23 replies 6 participants last post by  govmule84 
#1 ·
Hi all! I've not been around for a while, partly through illness, partly because I've not had to much constructive to say, so I've kept quiet! Anyway, it's nice to get a chance to ask a question.

I picked up a really nice Joe Hunt mag, at a VERY reasonable price a while back. I'm planning on putting it on one of my project Triumph twins at some stage (I've got my BSA head on at the moment!), but it came from a Harley. It didn't come with any of the associated Harley base assembly, or Triumph plate adaptors, so obviously I'll have to find them (I know I can get them new). But, apart from those parts, as well as a new correctly timed cam and a few other bits, should I be able to get it to work OK?

Thanks in advance!

PS, although I've not been posting, I've been checking what's going on, almost daily!
 
#2 · (Edited)
the bodies are the same it is all down to internals, yes you need a new cam in it and then find out which way it spins as there are obviously two directions it could run with the points in different positions depending if its a left or right spin spark,if you need it reversed you will need a new rotor with the correct cam profile and rotor for the pulse release to match a triumph,....Then there are 3 (maybe 4) places it can fit on a Triumph depending what year & model bike, .. some fit to the stock points hole on a unit construction, some will bolt on under the carb if it was fitted with a Lucas K2F or K2FC magneto on the left side driven off of the left side end of the front cam and there might be (I cant remember) able to be fitted to where the Dynamo fits on in front of the motor, so decide where you want it mounted and work out if you have one that sparks in the desired direction for your chosen placement...…...
 
#3 · (Edited)
A long time I haven't looked at that problem...

At a guess, a vertical twin Fairbanks/Hunt mag has symmetrical North and South poles on the rotor, ie spaced at 180 degrees to give full sparks at every 360 deg of crank revolutions.

To get the best spark, a 45 deg Vee Twin rotor will have its North and South poles slightly off by 22.5 deg to give full spark at 167.5 deg then at 202.5 deg on the mag = equal best sparks at 315 deg then at 405 deg on the crank (added = 720 deg, 2 crank rotations)...

So not just a quick cam swap, you need the full Triumph rotor.

If that Vee angle is not on the rotor, it will be in the body, so that would be a body and cam change, most unlikely...

Patrick
 
#4 ·
Well, thanks for the info Magnum4pete and Patrick. Although I'm not sure how that would work Patrick. I understand, and rebuild mags (I carry a stock of about 100 Lucas and BTH mags). so not sure how it's possible to offset the poles of a magnet you're using to induce an EMF (Electro-Motive Force, or Voltage). Am I not right in saying the magnet (Rotor) creates the voltage as it spins within the coil (Stator), with the poles at 180 degrees, then the Cam induces the spark, by interrupting the flow of voltage, at the degrees of initial lift, the degree at which the points open? On a Lucas K2f, and BTH, the rotor has the coil, which spins inside the Magnetic stator, which is the other way round. Both are dependent on the points cam.
 
#7 · (Edited)
To see how a rotor can have offset poles, just try to imagine the body and the inners of a 4 pole rotor for a 4 cylinder magneto, 360 degrees, 1/4 circle magnet, 90 deg spacing 1: N S then 1/4 circle magnet 90 deg spacing 2: N S to give 4 sparks per rev at 1/2 crank revs at every N S N S...

Put 4 magnets on rotor at every 45 deg = 8 poles magneto to fire an 8 cylinder engine with a 1/2 engine rev magneto.

Done enough HDs in me life to know their 45 deg mag cannot fit a vertical twin as is...

Patrick
 
#8 ·
I do rebuild mags, but only Lucas and BTH at the moment, so there are major gaps in my knowledge! When I trained as an electrician, they didn't teach you everything about electrics, just the stuff you needed to know. I'm beginning to understand about Joe Hunt Mags now, thanks for your help!
 
#10 · (Edited)
if I were you i'd give Dave Shaw a call at Morris Magnetos, he is a real friendly fella who as good as wrote the book on Fairbanks Morse type Magnetos, he will also have everything you need to convert yours to what you want if it is possible,.... he as also got a few video's on youtube you might find of use, his number is,..... 973-540-9171
……………… https://shop.morrismagneto.com/products/tpl-replaces-lucas
 
#11 ·
And now, some tricky trivia...

Only one motorcycle make managed to run a 60 degree Vee Twin with a 180 deg flat twin/vertical twin cam spacing, so points firing every 180 deg on magneto...

Anyone cares to think/imagine how they did the deeds?

Patrick ; O )
 
#12 ·
I adore this question, as it requires big thinking on two separate topics. I'll try working my way through it. Maybe with clues I can get there.

The first question (what bike is it?) is intriguing, as the 60° twin never got much love until what...the 80s? But that's really getting on past the time when a maggie or points were being used, so that makes me think this bike is either esoteric or a weird race machine. It's going to be an odd little duck, for sure.

As far as how it worked... well, knowing the bike would make this easier, of course.

My initial guess is that whatever this bike is, it had a 60° splay between the jugs, but offset crankpins, making the 180° cam in the ignition unit (magneto?) usable.

Am I on the right track, or no, Patrick?
 
#14 ·
Then I am not completely wrong... it's esoteric ;) And I think my offset crankpins could be made to work, too, as long as we have a machine shop and I don't have to do any of the work.

Assuming this bike is that early, the manufacturer was likely adapting a magneto made for something else, hence the conundrum. I'm no closer to an answer, but I guess this was before Bosch started supplying mags with different slip rings for different machines. I'm leaning toward JAP... I know they used 60 degree engines early on. I don't know if they were that early. I think they used 50 degree too.

Fire would have to happen at 300°-420°-300°-420° etc. And since you asked on this thread, I guess it's not so simple as to just have the armature and poles offset by the correct amount; something else is in play here.

Now I'll pretend I am working at the motorcycle plant in 1912 or whatever.

So normally the eccentric bit, the "brain" of the mag, is the points cam. But perhaps the manufacturer didn't have the buying power to get slip rings made for such an odd bank angle. Or maybe it was so early such variety didn't yet exist, like Bosch began offering on their magnetos.

Maybe the manufacturer of the bike had to figure out how to use a commonly available commercial item on his uncommon motorcycle. That would mean building the "brain" would fall to him, not the magneto supplier... but it likely would still need some sort of eccentric component.

Did this bike use linkage of some sort between an eccentric item on the cam or crank (or whatever was driving the mag) and the magneto in order to come up with the odd firing pattern, maybe?
 
#15 ·
You're nearly there, Govmule…

Think about accelerating the mag to get to one spark (shorter travel time) and decelerating it to get to the next spark (longer travel time) and so on while the engine turns steadily...

By the way, it was the bike's own magneto, not a Bosch or other make. In fact, the whole of the bike except the tyres was made by the maker, including a very clever carburettor...

Think about it as watchmaker quality!!!

Patrick
 
#16 ·
Funny you mentioned that, because as I was puzzling this out, I thought about the guys who retard their mags on Harleys to kick. I decided that moving the mag body would be more effort and wear than was needed.

Now your last comment leads me to think it must be Swiss, so I started with Condor, the only Swiss bike I knew of. Now I've come across the Motosacoche, who made motors for Condor, but apparently before that they tried their hand at their own thing.

I can't find much in the way of pictures at all though, but I see MAG used weird-o vee angles, and one pic I found shows lead positions on the mag that make me think it's a 180 mag.

Maybe the poles inside the mag are moved back and forth mechanically with some sort of external eccentric (like a Stephenson gear) while the armature speed stays constant? Easy enough to make, and could be made adjustable. I think something spring actuated would be too sloppy... but then again, early engines probably weren't that demanding.
 
#19 · (Edited)
Yes, it's Swiss but no to the restl!!!!!!

Firing cams are 180 deg apart, single set of points, so really firing at 180 deg and no moving parts on magneto except advance lever and rotor (turning round, slower, then faster, then slower then faster to create the Vee gap...…)

… A dream solution from the French speaking side of Switzerland!!!...

Patrick
 
#21 · (Edited)
Hi,



See photo of Moto Reve Vee Twin timing case!!!

The gear on the magneto is eccentric, its meshed gear fixed on the idler gear below has the same eccentricity.

Hence the magneto keeps speeding up (furthest out teeth to nearest to center = less crank degrees travel) and slowing down (nearest to center teeth to furthest out = more crank degrees travel) in one revolution and gives the sparks at the right moment on each cylinder of that 60 degree Vee Twin.



Weird but it works quite well as long as these two eccentric gears are meshed properly!!!

And designed with no computer for the complex maths...

Patrick
 
#22 ·
A) What kinda bike is it?
B) Why? This is so needlessly complex.
C) I can't even imagine the tax this would place on my brain if I was charged with figuring out something similar. Actually, I guess I could do it in a few hours, but shit, what a pain.
 
#24 ·
Oh, I missed the Moto Reve part.... that like didn't load on my computer or something.

That's pretty incredible. They learned so much so fast... and there were so many small companies making this shit happen.

Too cool.
 
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