timing a 1924 j.d. mag engine. need help.

[rwm]

here comes a can of worms tommo.why cant i take a 45 degree mag and pull the key out of it? rotate the the mag gear and make it a 42degree? see the can of worms? later tonight i'll post photos of some mag parts so everyone can see what we are talking about.

[Tommo]

I took myself up this garden path didn't I and yes Rob it's a real can of worms that can lead to serious arguements as opinions vary greatly on this subject.
My first observation would be the question, why would magneto manufacturers make several different versions of the same magneto if it wasn't necessary?
Now to your question Rob. The ramps in the interrupter ring decide when the mag is going to fire and by changing the position of the mag drive gear only changes the relationship of that firing to the position of the piston and does nothing about changing the mag from 42 to 45 or whatever degrees that the mag fires at.
A 45 degree v twin will run on a 42 degree mag and visa versa but staying with the first example, 45 with a 42, once timed on one ramp the second cylinder will be 6 degrees out ( 3 degrees at the mag = 6 degrees at the crank). So someone says my Harley doesn't run as good as it should, gets hot on one cylinder and at starting it sometimes spits back on one cylinder. Reason; one cylinders timing is not correct.
If you put a 45 degree interupter ring onto a 42 degree mag you can overcome most of the problems and it will work well so long as the mag armature is in excellent condition but if the armature is at all dodgy you will start to have trouble.
Reason armatures are built so that the maximum magnetic flux occurs at the time that the points break and that is why Bosch stamped all their armatures with the degrees that that particular armature was intended to be used at.
It's early in the morning here and there's a hell of a storm happening but as soon as I can I'll take some pictures of armatures and interrupter rings and put them up for you guys.

[Tommo]

I've taken shots of a 45 degree armature and one for a 180 degree flat twin Harley.
I don't have armatures for 42,50, 55 and 60 degree mags that are out of mags at present but feel sure these two can illustrate the differences.
The 45 degree armature is on the top and notice how the pole shoes have notches out of them and that how the notches are at opposing ends of the armature. One pole shoe has the notches at the drive end and its mate has its notches at the points end. Best seen in the second photo.
The 180 degree one has parallel pole shoes.
The pole shoes as they pass the magnet determine the point of maximum magnetic flux and now I'm out of my depth as I don't understand how the pole shoe shape effects this but experience has shown me that it does.
I don't think my photo is good enough but you may be able to see 45 stamped on the pole shoe in the first shot and take it from me all the other respective armatures will have their respective degrees stamped on them and all their respective pole shoes are subtly different.
Please note that we are talking Bosch mags and Bosch mags only here.
After my previous post two words came to mind that help when playing around with mags.
WHEN and WHERE
When; The points determine WHEN the spark occurs.
Where; The mag drive gear and it's associated gears determine WHERE the spark goes.
I know one relies on the other and it is simplistic to make a statement like this but if you bear this in mind it will help a lot in getting the best out of your equiptment.
Sorry about the quality of the photos but it's the best I can do with the gear that I have.

[Tommo]

Now interrupter rings.
Top left; 42 degree v twin notice the long ramps.
Top right; 45 degree v twin with small short ramps
Bottom; 180 flat twin with ramps dead opposite one another

One of the most important points is the positioning of the ramps in relation to the advance slot and I'll show this in a further photo but by now you will be starting to see that can of worms that Rob opened up and realise that when we get a mag that over the years has had all these components mixed and matched up it is no wonder that trouble occurs.
In most instances they spark and appear ok but in reality they are far from satisfactory and cause more trouble than they are worth.
Most good magneto overhaulers will have a machine with a 360 degree disc that will tell them exactly when the mag is firing and if you're really fussy they can stone the interrupter ramps so that the two sparks occur in exactly the right place.

[Tommo]

Advance slots
I've positioned all the advance slots to 12 o'clock and from that you can see how the positioning of the ramps vary.
Keep in mind that you are looking at them from the back but it must be obvious how mixing and matching opens up Rob's can of worms.
I don't overhaul mags but have a very good friend that does.
50 plus years of playing with them has taught me a lot but I don't know it all and if anyone disagrees with me go for it because I feel I'm never too old to learn.
One thing I do know about electricity is you don't see it coming and when it arrives it bites and generally arrives at the most unexpected times.
Enough one finger typing for now I'm out to brave the elements

[John Mertens]

thank you Tommo. boy i never know there was so much to mag.judging by your pictures and all the info i'm sure i have the correct mag for my bike. i got my Mag from Marks new rebuilt. had problems with it right away. sent it back to them and had them rework it. they said the condenser was no good. the company that made them for them went out of business. and that they got a batch of bad condensers. now Marks gets there condensers from a company in China.it's seams to work fine. but i'm still worried. made in China.????????? again thank you .Johnny.

[rwm]

thanks tommo this is how a forum should work.don't put that coffee can away yet.i'm gonna fill with some more worms.if i ever get this mad apart