Ignition Timing

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
Johnobirches
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Re: Ignition Timing

Post by Johnobirches »

Hi Spokefoot,

You say you put your finger in the plug hole and felt the piston come up - that could be the exhaust stroke not the compression stroke. Check also that the valves are both closed.

Good luck.

John
SPRIDDLER
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Re: Ignition Timing

Post by SPRIDDLER »

Johnobirches wrote:Hi Spokefoot,

You say you put your finger in the plug hole and felt the piston come up - that could be the exhaust stroke not the compression stroke. Check also that the valves are both closed.
That's a good point John, as I did wonder when Chris wrote:......
spookefoote1956 wrote:I think so. I put my finger in the spark plug hole and kicked over until it started to push my finger out. Surely that's under compression?
Using the kickstart is not the way to get the necessary accuracy: Position the bike with the rear wheel clear of the ground in 4th and turn the rear wheel.
Last edited by SPRIDDLER on Fri Jul 14, 2017 1:49 pm, edited 1 time in total.
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dave16mct
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Re: Ignition Timing

Post by dave16mct »

I always remove the tappet inspection cover and watch the motion of the valves as you turn the engine over with the back wheel, in 4th gear. (Sometimes I watch TV too.) Then you can see the inlet valve closing, you know it's the right stroke. Come on Chris, we want to see this bike soon!
Dave.
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Re: Ignition Timing

Post by 56G80S »

I also follow Dave's route with the tappet cover - it only takes a moment to do - inlet, compression, power, exhaust.

Although Sprid managed to make this read once, suck bang blow, I wonder if he had his mind on the job (!).

Johnny B
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Re: Ignition Timing

Post by SPRIDDLER »

56G80S wrote:I also follow Dave's route with the tappet cover - it only takes a moment to do - inlet, compression, power, exhaust.

Although Sprid managed to make this read once, suck * bang blow, I wonder if he had his mind on the job (!).

Johnny B
* [squeeze]

Don't forget the SQUEEEZE, Gromit. Most important, the squeeze ;) . (Fancy a Yorkshireman forgetting the squeeze :roll: )
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spookefoote1956
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Re: Ignition Timing

Post by spookefoote1956 »

Cheers how does 1/2" BTDC translate to degrees?
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Re: Ignition Timing

Post by SPRIDDLER »

spookefoote1956 wrote:Cheers how does 1/2" BTDC translate to degrees?
Do keep up Spooky! It's in the clip from the Owners Manual that I posted for you in my reply of 12th (a couple of replies above): 39 degrees.

(You have to slide the bar at the bottom of my clip in that post to the right then it will display the timing as 39 deg and 1/2").

Maybe I need to add that although you have an N1 mag 39deg and 1/2" are 39deg and 1/2" regardless of whatever mag is fitted.
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spookefoote1956
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Re: Ignition Timing

Post by spookefoote1956 »

Cheers pal. Funny enough I was just reading that very item! Sorry, it's been one of those days.
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Re: Ignition Timing

Post by SPRIDDLER »

No worries. I snipped the data in my post from the link (repeated under) that I gave you for the Owners Manual (see Page 6).

http://archives.jampot.dk/book/Owners_m ... Manual.pdf

Save that link as you'll no doubt need other info that's in the Manual.

And the Spares List for your '56 Model 18 (engine) is here:

http://archives.jampot.dk/book/Spares_l ... S_18CS.pdf
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spookefoote1956
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Re: Ignition Timing

Post by spookefoote1956 »

I have a plan for timing the ignition. I've got a timing disc that I'm going to connect to a socket via a bolt and then onto the lower nut in the mag chaincase. It will save me taking the primary chaincase apart. Any thoughts on that Spridds?
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All my bikes are original........ to me!
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