Distributor Position

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Location: DENMARK

Re: Distributor Position

Postby ajsph » Tue Jan 14, 2020 6:31 pm

the distributor need to be in good condition, with no wear in the bushes , then it will advance very smooth, no problem with the gears when the engine is running.
Poul

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Re: Distributor Position

Postby Chessiegolf » Wed Jan 15, 2020 5:22 pm

Ok Chaps,

Thinking caps on please.............with the tank and plugs removed I found it was easier to use the marked wire method to find 11/32 BTDC as I could not hold the vernier and rotate the engine at the same time. What I did find easier was to put the bike in 3rd gear and turn the back wheel, this gave a very precise positioning of the piston. Having placed the engine at 11/32 BTDC I duly released the distributor clamp and rotated it 180 degrees, changed the LT wire (which was the original object of the exercise) made sure the distributor HT lead nearest the engine went to the left hand cylinder and then put everything back.

No start of the engine, not a glimmer. So I released the clamp again, rotated the distributor more or less to where it had been, swapped the HT leads and it fired up straight away.

What I didn't check prior to finding TDC was that the engine was coming up on the compression stroke, could that be the trouble and that simply rotating the distributor put the whole ignition system 180 degrees out? I can now go back and make sure the timing is spot on with the distributor in its current position, but would like to have the LT wire at the top and the HT leads going to the cylinders as shown in the manual just for originality.

Thoughts please.

John

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Re: Distributor Position

Postby McBob » Thu Jan 16, 2020 12:55 am

Have you tried removing the dowel from the timing gear, turning the rotor 180 and refitting

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Re: Distributor Position

Postby Chessiegolf » Thu Jan 16, 2020 8:52 am

No, I've done nothing other yet than rotate the distributor 180 degrees and swap over the HT leads.
My thoughts are that rotating the distributor has only achieved putting the cylinder 1 HT output to the cylinder 2 position and vice versa, so I've probably ended up with the sparks occurring at the end of the exhaust stroke.

My guess is that when the engine was rebuilt, the distributor was fitted 180 out of phase so hopefully if I withdraw the distributor, check that the inlet valve has closed, set the piston to the 11/32 BTDC position and refit the distributor so that the rotor is more or less at 10 o'clock, as in the manual illustration, that should be a good start point.

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Re: Distributor Position

Postby willowbedone » Thu Jan 16, 2020 5:02 pm

Hello John
Yes I think you have timed it to fire on the wrong stroke .whilst turning by hand put a finger over said plug hole to feel compression Then set it at required distance before TDC .And check rotor arm is pointing to correct HT lead in distributor .Set timing and give it kick if it does not start try swapping HT leads This would let you know what
Not set right if it then starts
Ian

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Re: Distributor Position

Postby Chessiegolf » Tue Jan 28, 2020 5:16 pm

Just an update....

I've rotated the distributor again, retimed the engine taking reference from the left hand cylinder, making sure that I was on the stroke following the closure of the inlet valve and set the points (using a lamp) so that the lamp just comes on at 11/32 before TDC plus full advance (achieved by twisting the rotor clockwise against the springs). I then checked the rotor position and it was at 3 o'clock, which is the firing position for the right hand cylinder, so connected the rearward HT lead to the right cylinder. The motor fired up and ran fine, so the problem, if there is one, is that a previous owner/mechanic has fitted the distributor 180 degrees out of phase. Apart from not replicating the diagram in the manual, its not a concern as I now have the LT connection at the top and its easier than before to check the points.

I've updated this post as in a later one of mine (Sparking Coil) I wanted to check everything I could about the ignition system. The only fault I could find was that the HT lead into the distributor didn't seem to have a decently terminated end. Only 2 or 3 of the strands were trapped under the ferrule, the rest were just floating in the end gap. Having made off the end again there are now no errant sparks from the coil.

Frustratingly we've had rain today, but once the roads dry off again I'll go for a ride and make sure all is well when all the parts have got to working temperature.

John

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Re: Distributor Position

Postby Chessiegolf » Wed Jan 29, 2020 7:55 pm

It was a nice dry day today so having covered 56 miles without missing a beat, I'm optimistic the problem has gone away. The only things I believe could make any difference were to swap over the plugs and to re-terminate an HT lead.
However its running fine just now so can declare the coil not to have failed prematurely.

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