Timing 1957

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
Winchboy
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Timing 1957

Post by Winchboy »

Hi,

1957 G3LS was running fine, went to it the next day and it wouldn't start. After a load of kicking and checking the obvious I got an almighty back fire. Got a healthy spark, new spark plug, checked the gap, remade HT lead with new plug cap, cleaned pickup to HT lead from magneto, cleaned points and healthy spark across them, checked points gap of 12 thou. What I have noticed is that the points are open for the entire cycle APART from when at TDC, either I am going mad or this is the total opposite of what it should be.

All I can think is that the timing has slipped somehow. As far as I know to do this it would be: Remove magneto sprocket, take piston to 7/16" BTDC, set points gap, refit magneto sprocket (making sure not to move the magneto shaft to not upset timing), then the magic should happen inside the mag at the right time and my bike is running again? First time doing this so any advice greatly received.

What is this contraption on top of the magneto sprocket? Tried to undo the nut it undoes a couple of turns but then just spins without undoing? No split links in chain. Tried a couple of 2 leg and 3 leg pullers I have but the feet of all of them fouled the back of the alloy timing case.

Many thanks!
1109BC3F-C8E4-4FB9-9286-1D23819A86E2_1_105_c.jpeg
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dave16mct
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Re: Timing 1957

Post by dave16mct »

That's the auto advance mechanism. Firstly make a small wooden wedge to keep the auto advance advanced. Then don't touch it. Loosen the bottom sprocket nut a bit and pull it off it's taper so it's just loose. Set the points to 12 thou. Then set the piston to 7/16" before top dead centre, making sure both valves are closed (on compression stroke. Turn the mag in the right direction until the points just separate, thin rizzla between them just pullls free. Then tap the sprocket back on it's taper with a socket and hammer. Tighten the nut and check the timing . Don't forget to remove the wedge!
Dave.
PS the bolt on the auto advance is supposed to extract it when unscrewed. Perhaps you didn't turn it enough?
Winchboy
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Re: Timing 1957

Post by Winchboy »

Thanks for that, how can I undo the bottom sprocket nut without the engine turning? Put it in gear and press the back brake? Thanks for putting it in layman’s terms! How do I know which way will be advanced or retarded?
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dave16mct
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Re: Timing 1957

Post by dave16mct »

Top gear, ring spanner on the nut. Tap with Thor mallet or similar. From the points side they turn clockwise. The auto advance should be retarded until pulled against the tension of the springs. They should return easily, eg snap shut.,but may be a bit sticky or lazy if they have rust or old grease inside. You may have to clean it out with parafin or WD40.
Dave.
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dave16mct
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Re: Timing 1957

Post by dave16mct »

You can see all this in the Instruction Book in the archives. Click on the box with 3 lines (top left) click on jampot.com, which takes you to the home page. Hover over Club and follow the drop down list to Archives.
Dave
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clive
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Re: Timing 1957

Post by clive »

And put a fair wadge of grease on that chain. If the advance does not snap shut it may be that the chain is too tight. Looks like it might be in the photo.
clive
if it ain't broke don't fix
56G80S
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Re: Timing 1957

Post by 56G80S »

It's difficult to tell but it looks like the large aluminium "washer" nearest the mag isn't seated correctly (no time to check spares list numbers). There are two small holes opposite each other near the edge of the large washer and these should register with two small prongs on the main ATD mechanism.

The next washer out from the mag is different to mine (1956). Take a look (as advised above) at the manual and parts lists for the bits you should have.

I used white spirit to clean out the rust and grease from inside a sticky ATD as advised by the now deceased Rob Harknett and this worked well.

Johnny B
Winchboy
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Re: Timing 1957

Post by Winchboy »

Following this through now, set the gap to 12 thou but when rotating the shaft the points seem to plebe open for almost half of the revolution? Feeling the shaft there seems to be two cam shapes on it? I thought the points should only open momentarily ?
Groily
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Re: Timing 1957

Post by Groily »

Points are typically open much longer than they're shut on a single cyl magneto. It takes about a quarter of a revolution with them closed to charge the coil for the next spark. The lobe on the cam is pretty wide to ensure they stay open a goodly while. I don't think you have much to worry about - on that score anyway!
Winchboy
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Re: Timing 1957

Post by Winchboy »

Bike is now running great, thanks for putting up with my questions! Most helpful
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