Author Topic: A7 timing  (Read 406 times)

Offline pdg

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A7 timing
« on: 04.11. 2014 22:55 »
I'm taking the magneto off to be refurbished. Two questions spring to mind about refitting:

1. Is it necessary to take the head off to measure the the recommended distance to TDC or is there a less painful way of doing it?
2. When you tighten the nut for the pinion drive how do you hold the contact points in position?
3. How tight does the nut need to be?

Many thanks.

Online muskrat

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Re: A7 timing
« Reply #1 on: 05.11. 2014 05:54 »
G'day pdg.
There are lots of methods, and most have been posted on here. Try a few searches for timing.
Most here use the old stick down the plug hole, I use verniers. With the stick down the hole rotate engine till top of stroke (rock back and forth to get it spot on). Mark the stick adjacent to a point on the head. Remove stick and mark it 5/16" - 3/8" (depending on type of engine and cam) higher. Turn engine backwards, replace stick in hole and turn engine till the top mark is adjacent to the head point.
To hold the points you can use a small timber wedge (1/2 timber cloths peg) between the points post and cam ring (careful not to distort the post). I had a spare earth brush screw with a timber dowel in it to screw in to hold the armature.
You don't say whether it's auto or manual advance. For auto the other half of the cloths peg can wedge it into the full advance position. Do not try to seat the taper until the nut has been done up a few turns. Push the unit home and keep pressure on it till the nut takes up and tightens. If the taper is a good fit it shouldn't turn whilst tightening the nut up to about 10-15ft/lb's. Take out the pegs and turn the engine backwards and back up to your marks. Place a cig paper between the points and work the auto unit. The cig paper should just start moving when the unit reaches it's stop.
You may find you have to do it a few times (if the taper doesn't hold) and fudge it a bit to end up with the right setting.
Good luck, it's not as frightening as it sounds.
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Muskys Plunger A7


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Re: A7 timing
« Reply #2 on: 05.11. 2014 07:42 »
There's a good step by step guide on the Cheshire BSA website, also they have a good list of recommended suppliers and service engineers.

Offline pdg

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Re: A7 timing
« Reply #3 on: 05.11. 2014 08:48 »
Many thanks. That's really helpful.

Regards, Peter.