Magneto Timing Again

So what is the secret to keeping the magneto shaft from moving when you tighten the magneto extractor bolt on the sprocket/AAU? I just retimed an Atlas. I have done this this dozens of times on different bikes. Sometimes after I set the points to break open at 28 to 32 btc (depending on which timing theory I happen to be adhering to at the moment) I can tighten the magneto extractor bolt and nothing moves. Other times I have to keep experimenting with setting the points to break retarded more or less as much as the timing moves when I tighten the bolt, until it ends up in the right place. I know Bernie Nicholson in Modern Motorcycle Mechanics recommends giving the bolt a whack to set the sprocket against the taper on the magneto shaft. I confess that I have tried this on occasion, with mixed success, but it strikes me as a very unsympathetic way to treat the magneto bearings. So what is the lost technique? This timing "system" has been around for ever. The old timers in their sheds must have figured out a reliable secret approach. Anyone know?

I simply press the AAU on the taper when I think the setting is right, and tighten bolt finger tight. Then I check if points break where I want, if so, tighten bolt fully. I do not recall ever having any shifting of the timing after tightening fully. Sometimes, if I have to move the AAU because the points are not breaking at the set point I want, I find the finger tight bolt has secured the AAU so well that I have to resort to my gear puller to get it loose again (my extractor bolt is stripped). That behavior shows there is no movement in the AAU relative to the magneto shaft, even with only finger tight pressure.

Perhaps the timing shift you are seeing is in the contact breaker assembly ... either due to a sloppy fit in its taper, or play in the various pieces making up the assembly.

Slick

You don't give the bolt a whack, you give the sprocket a light tap. Use a socket against the sprocket to clear the shaft and a light tap should lock the sprocket in place on the taper. Then tighten the nut. It doesn't need to be really tight though.

You've both given me something to think about. I'm now going to triple check to make certain neither the cam ring nor the contact breaker assembly is loose. Also rapping the sprocket instead of the bolt is logical and probably a major improvement over my current "technique."

Roger that the cam ring may be rotating back and forth. Check the gap at 6 o'clock on the grub screw.

Slick

texasSlick said:

Check the gap at 6 o'clock on the grub screw.

Click to expand...

Is this not a phasing adjust eccentric set pin? To set cam ring anticipated point opening to synchronize with maximum primary current caused by magnetic field flip? Different mags have it set at different rotational positions.

dynodave said:

Is this not a phasing adjust eccentric set pin? To set cam ring anticipated point opening to synchronize with maximum primary current caused by magnetic field flip? Different mags have it set at different rotational positions.

Click to expand...

Yes it is, Dave. It can also be used to tweak the timing a degree or two +/- if one is not concerned with being on the maximum flux peak.

In this case, I am thinking the gap may be excessively wide, the grub screw loose, and the cam ring may be shifting, causing the timing shift the OP is getting.

Slick

You might also try lapping in the sprocket to the taper with valve grinding compound. That way you will be sure that the sprocket is fitting properly and it will be less likely to move as you snug things down.

Bodger said:

You've both given me something to think about. I'm now going to triple check to make certain neither the cam ring nor the contact breaker assembly is loose. Also rapping the sprocket instead of the bolt is logical and probably a major improvement over my current "technique."

Click to expand...

One of the techniques I learnt using a K1F mag with a manual A/R was to use fine valve grinding compound between the mag taper/sprocket then washed off with petrol. The same would apply to the K2F.

I wonder if a very quick burst of an impact wrench would do the trick.

well from what i have read here no wonder your having problems first of you need to time your norton engine from the left hand cylinder or the drive side and then find on the magneto the spark plug lead next to the battery box or farthest away it's this plug that fires first ,then turn the point so the contacts are looking upwards the heel of the contact will on the cam dunwell at the bottom right next is to get the ATD in full advanced by slotting a small bolt in the advanced mechanism so it remains open then with and adt bolt fully slack you can then set up the timing by getting the left hand cylinder on TDC with the valves closed so you may need to remove all rocker covers to do this, next fit your timing disc on TDC and verify you have TDC and both valves are fully closed on the left hand cylinder this is your set up procedure, then you can turn the engine back to 32% and get the point so there just about to open and with a small 1/8 spanner hold the small bolt on the point end then do up with your fingers the ADT bolt it will tighten but keep going as it will slack of and then tighten again the ADT has a double locking thread inside the sleeve bolt, once tight just check you have things all right and you should find the point with be fully open at 6 to 8 degrees after top dead center and do not forget to remove the small bolt holding the atd mechanism open so good luck with this,

Hi Anna, It's a shame that your post is infected by so much negativity. I left all steps up to your comment about the1/8 spanner out of my initial post because I thought it was clear that I had got to that point as a matter of course. Your suggestion to hold the point plate bolt while finger tightening the taper bolt does seem like an effective technique. So as per my usual practice I will forgive the poor bedside manner in exchange for the (hopefully) effective treatment proposal.