Mag Timing Sequence

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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spookefoote1956
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Mag Timing Sequence

Post by spookefoote1956 »

Hello again. I've fitted the new (to me) N1 from our wonderful spares dept at Kettering and just want to check I'm doing the correct sequence for timing.
1. Put bike in gear 4th
2. Loosen mag nut in casing
3. Fully advance timing lever. Find TDC compression stroke. Check pushrods rotate, valves are closed.
4. Roll rear wheel back so that timimg tool in spark plug hole is 1/2" BTDC
5. Put fag paper in points and turn until it can be removed.
6. Tighten mag nut.

Or

Is it better to leave the mag nut tight and adjust the opening and position of the points via the Contact Breaker Securing Screw.
Hail Joe Lucas ............ Prince of Darkness!
All my bikes are original........ to me!
"Creativity is your intelligence having fun" Albert Einstein
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ajscomboman
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Re: Mag Timing Sequence

Post by ajscomboman »

Leave the mag nut tight and loosen the camshaft sprocket nut, you'll find it much easier to set the timing. As you have mentioned find TDC on firing stroke using the wheel in 4th gear, move backwards dropping the piston below 1/2" and then slowly bring back up to 1/2" as it removes any backlash. Rotate the mag points till they are just about to open then using a socket larger than the nut tap the camshaft sprocket back onto the taper and lock up the nut.
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spookefoote1956
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Re: Mag Timing Sequence

Post by spookefoote1956 »

Thanks, much appreciated
Hail Joe Lucas ............ Prince of Darkness!
All my bikes are original........ to me!
"Creativity is your intelligence having fun" Albert Einstein
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Re: Mag Timing Sequence

Post by SPRIDDLER »

That's what I do except that I find it easier (more controllable to prevent inadvertent movement) to loosen the nut of the cam driving sprocket rather than the one on the mag. A sharp tap on the cam sprocket (using an oversized socket) tends to set that sprocket in place whilst I tighten its nut, then check point opening point again.
The mag armature shaft has little resistance from unwanted movement after setting its position and the armature has a 'flip point' at the points-opening position which makes it more difficult to keep it in the required position. If the sprocket nut is just loosened enough to be able to turn/set it to the required position there's more resistance to prevent it from turning.

(Ooops, I see my reply has crossed with Rob's).

EDIT - It's probably unnecessary to mention that the points gap should be set before doing the timing.
Last edited by SPRIDDLER on Thu Jul 21, 2022 8:03 pm, edited 1 time in total.
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ajscomboman
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Re: Mag Timing Sequence

Post by ajscomboman »

SPRIDDLER wrote: Thu Jul 21, 2022 7:54 pm That's what I do except that I find it easier (more controllable to prevent inadvertent movement) to loosen the nut of the cam driving sprocket rather than the one on the mag. A sharp tap on the cam sprocket (using an oversized socket) tends to set the sprocket in place whilst I tighten the cam sprocket nut, then check point opening point again.
The mag armature shaft has little resistance from unwanted movement after setting its position and the armature has a 'flip point' at the points-opening position which makes it more difficult to keep it in the required position. If the sprocket nut is just loosened enough to be able to turn/set it to the required position there's more resistance to prevent it from turning.

(Ooops, I see my reply has crossed with Rob's).
Great minds and all that spring to mind Spridd's. ;) ;)
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Re: Mag Timing Sequence

Post by SPRIDDLER »

ajscomboman wrote: Thu Jul 21, 2022 7:59 pm Great minds and all that spring to mind Spridd's. ;) ;)
Hmm. I may have learned that from your great mind back in the early 60's.
(Going off-air now to treat my great mind to the bobbing pony tails in the Germany vs Austria women's Euro 22 football quarter final ;) ).
Last edited by SPRIDDLER on Thu Jul 21, 2022 8:41 pm, edited 1 time in total.
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spookefoote1956
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Re: Mag Timing Sequence

Post by spookefoote1956 »

The nice man from the spares said I did not need to check the points gap as it would be spot on and invalidate the guarantee!
Hail Joe Lucas ............ Prince of Darkness!
All my bikes are original........ to me!
"Creativity is your intelligence having fun" Albert Einstein
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spookefoote1956
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Re: Mag Timing Sequence

Post by spookefoote1956 »

https://www.youtube.com/watch?v=FcMe3zbnWsMFound this cracking video on youtube
Hail Joe Lucas ............ Prince of Darkness!
All my bikes are original........ to me!
"Creativity is your intelligence having fun" Albert Einstein
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Re: Mag Timing Sequence

Post by Joker_Bones »

I really like Dick Casey's videos, I've watched them all... Well all the AMC ones...
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Re: Mag Timing Sequence

Post by Joker_Bones »

I like using a multimeter to see when the points open... The resistance across the points changes from continuity to about 6 ohm (the resistance of the LT coil) just as they open.
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