Magneto points central screw

Now sorted, I was having issues timing the mag with the mag timing light ( thanks A.O. ) and it appeared something was moving erraticly , as though the points plate was loose. Turned out the spring blade was just kissing the cam ring. I assume the old brass bodied types are expensive because they're better than the cheap nasty new ones I bought.  Job done anyway.

Regards all

Damn magneto's.    Central screw fits fine, bearings good etc etc, BUT, setting the points the difference is way too big, no way will the points gap get anywhere near a few 'thou to each other.

Cam ring is exactly 180 so another strip and sort required - manual A/R so not so easy to do the shim trick to line it up.

 Back to square one - again !

Thanks George, perseverance it is. Originally, the points appeared 180 apart, but once I got the mag timing light, the more accurate result showed a 10 deg  firing error.   Points having a small gap and a big gap.  Bluing up the points plate taper showed it was'nt sitting true in the centre, some careful work with a fine file cleaned up the error each side of the location nib. No better.  Spotted the copper stud for the moving point was loose, at least that's now tightened up. Checked the cam ring, slightly oval on its outside face, a careful pinch in the vice sorted that. Slightly better. I've finally set the cam ring up in a rotary table and , with a fine point DTI did a full 360 survey of the cam forms, it now seems someone has tried to true the cam ring to 180 - not very well.  The challenge now  is to work out how and where to do some very delicate grinding  to sort the error and get back to 180 point breaks. 

There's about to be a no going back moment !

Well, after making a 4x scale drawing ( using an 8" timing to disc to draw around ) then  plotting the DTI dimensions on it every 10 degrees, joining the 36 dots up showed a non-symetric cam form. Should be mirror image. After some head scratching, since the cam ring was set true in the rotary table, I set the rotary table true central in the mill and with a rotary stone, ground away the extra thickness found on one side (where the points close) so both points closed areas were equal thickness. Rotated the stone around to where the opening ramp is, then moved the  mill table 180 deg and ground the other side so the rise points ended up at 180 deg.  It was an all or nothing job, but it seems I got away with it as the mag timing light now shows exactly 180 deg. The flux timing is difficult to judge, but it appears to have points just cracking a fraction after maximum . The points gaps are now as equal as feeler blades can tell. 

If it had been an ATD mag, packing the cam ring outside achieves pretty well the same thing, which is what prompted me  to correct the thickness , the closed distance from centre must be the same to enable the points to open an equal amount  ( ie from the same closed position ), as well as the lift point being the same. 

That's my theory anyway - I'm sure there will be other views on this !

She won't be back on the road 'till next year, fingers crossed .

Regards all, 

Terry.