Tightening the magneto sprocket fixing nut without the magneto spindle spinning?

[Colsbeeza]

Thanks Richard,
That is enough for me to go on. I see it does not leave a lot of meat at the slot ends does it.?!!
Colin

[orabanda]

There is enough however.
You can choose to reduce the length of the slot.
I use heavy duty (or high tensile) 5/16"flat washer under the nut.
Post some pics when you finish

[RichardL]

Where I am I can't read other posts. I use a slice of pink pencil eraser jammed between the two posts and the cam ring. This provides stability (because of the fri ction) while moving toward the points-open position and prevents running down the slope just as points open. Also, allows the pinion bolt to be loose enough make adjustments while avoiding stress on the brass locator in the points block. Finally, once in position, tap home the pinion with a socket over the bolt, then slowly sneak up on tightening the bolt. Fingers first, then light wrenching. Now recheck timing. Good? Final wrench tight and check again.

Well, that's about how I do it, at least.

Richard L.

[Greybeard]

...then slowly sneak up on tightening the bolt.

I like that! Should I be tunelessly whistling?

[LJ.]

Placing a screw or bolt in the earth track is a good idea, not thought of that.... BUT, I bet this is why so many earth tracks have deep grooves in them, like in photo, I've often wondered how the hell had that happened! I'd think that a brass screw or bolt would be safer than steel one. Or certainly some kind of flag or visual reminder that it is there before starting.

[Triton Thrasher]

If pressing the auto advance onto the taper with your thumbs doesn’t make it stick sufficiently that you can tighten the nut without the armature turning, then the tapered faces are not in good condition.  They can be ground into each other with valve grinding paste.

Avoid straining the fibre gear teeth, by sticking a screwdriver through the auto advance yoke and pushing against the turning force of the spanner on the nut.

[RichardL]

...then slowly sneak up on tightening the bolt.

I like that! Should I be tunelessly whistling?

It wouldn't hurt.

[RocketRick]

Ted, I like your solution of putting a screw into the earth brush hole.  The thread is 5/16 BSF.  I agree with LJ that a soft screw needs to be used. I would recommend a nylon screw if it is available, or fit a plastic tip to a steel screw.

[muskrat]

G'day Rick.
This is an old thread but thanks for your input.
Now get over to introductions and tell us a story.
Cheers

[groily]

Tis an old thread - but just worth maybe reverting to LJ's pic for a moment while the thread has folks' attention.
 
The track on the armature has not been created by the use of a bolt to hold the thing still when setting the timing.
It's been machined down to eliminate the dimples that are caused by the return current from armature to mag body via the earth brush at the firing point(s) of the magneto. The dimples can become deep over time and they affect the smooth running between brush and brass. One dimple is usually worse than the other on a twin (or a four for that matter) owing to the opposed polarity of the sparks.

The armature in the picture is a sad case owing to the depth of brass removed, which is pretty much to the depth of the steel dowel pins used to assemble the armature.  Filling in dimples with hard solder or braze and machining back to round isn't something I have experimented with - nor do I want to as a true fit on the coil is important and distortion is a risk. Probably 'do-able' though in extreme cases. In 95% of cases a light turn in the lathe is enough to recover the brass end cheek and the majority of rebuilt  mags for our bikes will show signs of this as it's part of the routine.

It is said that the use of an auxiliary earth brush on the rear of the contact breaker can reduce the risk of deep dimpling caused by the main brush, as the earth path is shared, but I have to confess to mostly using cb assemblies not so equipped on my own bikes. None of the later 'low inertia' steel cb units has the facility for a brush in any case.

[bikerbob]

I have never used a bolt in place of the earthing brush but were I to do so I would not use a steel or brass bolt as they colud mark the brass on the armature so creating the possibility of premature wear on the earthing brush. I would remove the brush and spring then turn a piece of nylon so it was a push fit in the earthing bolt and the correct length so when tightened down it would grip the armature, it would not have to be very tight to hold it while fitting the ATD onto it's taper.

[Angus]

Hi All after reading this and needing to time another make (triumph), I found a spare earthing bolt, a small piece of dowel and glued that in. It appears to hold really well  though not actually used it yet as other problems manifested themselves