Distributor Position

Information relating to the Matchless G12 or AJS Model 31 650cc twin
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Distributor Position

Postby Chessiegolf » Fri Jan 10, 2020 4:54 pm

I've just rewired my 1960 G12 having fitted a 12v alternator. The only cable now to change is the low tension from the coil to the distributor. For some reason the wire is at the bottom of the distributor and the HT cable nearest the cylinders goes to the right hand cylinder, this is not as the picture in the manual. Presumably I could rotate the distributor 180 degrees and reverse the HT leads? This would then put the LT wire at the top and make access to the fixing post so much easier.
Any thoughts please.

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Re: Distributor Position

Postby willowbedone » Fri Jan 10, 2020 6:47 pm

Sounds like an easy fix I cannot see any reason why this should not work
Ian

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Re: Distributor Position

Postby Chessiegolf » Fri Jan 10, 2020 7:30 pm

Ok Ian,

Thanks for the reply. I didn't like to slacken the clamp until I had checked.

The engine starts and runs fine though I've no idea if the timing is optimum. While I'm repositioning the distributor I might as well check the timing. The manual states to find TDC with a rod on a piston and then turn the engine backwards so that a mark on the rod 11/32" higher up aligns with the original TDC position. The question is, is it ok to turn the engine backwards by way of the large nut on the alternator rotor (the primary chaincase cover is removed just now)? I have a Gunson inductive timing gun so could use that but do not know if there are any manuafacturer timing marks to use or if I have to mark the rotor myself. Again the manual says that 11/32" equates to 35 degrees, so can I just measure and mark 35 degrees from the TDC position on the rotor and use that.

Sorry to be asking stupid questions!

John

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Re: Distributor Position

Postby willowbedone » Fri Jan 10, 2020 8:02 pm

Hi John
Its ok to turn the engine on the rotor nut especially with spark plugs removed .I think you will have mark your own timing marks as none are put on by amc .Be aware of static timing or actual advance when auto advance unit advances timing when engine is running and setting timing with a strobe light.Make sure distributor does not have offset lugs before turning 180 degrees .Might be best to find tdc then turn engine back by required amount then set distributor
Ian

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Re: Distributor Position

Postby Chessiegolf » Fri Jan 10, 2020 8:32 pm

Ian,

Thanks again. My intention was not to remove and refit the distributor, just release the clamp and rotate through 180, if it hits against any kind of stop then I'll abandon the idea.
You are probably right about using the timing light as it will need quite a few revs I'd think to ensure full advance. The manual says to rotate the distributor rotor to simulate full advance and then set the points gap. This is probably the safest way and I guess we are not chasing the last bit of power, but it would be good to know though that the timing is somewhere like right, and not over advanced. The engine occasionally kicks back when starting but that may be because I've not got the fastest swing in the world.

John

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Re: Distributor Position

Postby MalcW » Mon Jan 13, 2020 9:35 am

Chessiegolf wrote:Ok Ian,

Thanks for the reply. I didn't like to slacken the clamp until I had checked.

The engine starts and runs fine though I've no idea if the timing is optimum. While I'm repositioning the distributor I might as well check the timing. The manual states to find TDC with a rod on a piston and then turn the engine backwards so that a mark on the rod 11/32" higher up aligns with the original TDC position. The question is, is it ok to turn the engine backwards by way of the large nut on the alternator rotor (the primary chaincase cover is removed just now)? I have a Gunson inductive timing gun so could use that but do not know if there are any manuafacturer timing marks to use or if I have to mark the rotor myself. Again the manual says that 11/32" equates to 35 degrees, so can I just measure and mark 35 degrees from the TDC position on the rotor and use that.

Sorry to be asking stupid questions!

John


Should be fine. However, what you should do is go back past the 11/32 mark and then come forward, to take up any backlash in the gear train. What I do with my bike is use a vernier gauge. I extend it, the put the rod down the plug hole, with the piston somewhere near the bottom, and the end of the vernier scale resting on the cylinder head. Then rotate the engine slowly forward, holding the vernier still, so that the piston pushes the rod up. Once past TDC, remove the vernier, note the reading, extend it another 11/32 and lock it. I can then move the piston back down, replace the vernier as before, and turn the crankshaft forward slowly until I just feel the piston touch the vernier rod.

Malc

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Re: Distributor Position

Postby Chessiegolf » Mon Jan 13, 2020 3:24 pm

Malc,

That sounds like an excellent suggestion, I'll do exactly as you've described.

I just need this cold spell to pass so that I can get into the garage again as I also need to remove the tank, check the tappets and oil flow to the rocker compartments after the extensive overhaul and reposition the alternator cables which had been fed through the upper hole in the crankcase and the lower hole sealed!

Thanks

John

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Re: Distributor Position

Postby MalcW » Mon Jan 13, 2020 4:26 pm

Chessiegolf wrote:Malc,

That sounds like an excellent suggestion, I'll do exactly as you've described.

I just need this cold spell to pass so that I can get into the garage again as I also need to remove the tank, check the tappets and oil flow to the rocker compartments after the extensive overhaul and reposition the alternator cables which had been fed through the upper hole in the crankcase and the lower hole sealed!

Thanks

John


If you're going to remove the tank anyway, you'll be fine. The only snag with the vernier method is that whilst with a piece of bent wire you can check the timing with the tank in place, with the vernier you can't, as there isn't enough room. I have considered using the vernier readings to make an accurate piece of bent wire for future use, but like most things...

Malc

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Re: Distributor Position

Postby ajsph » Tue Jan 14, 2020 3:50 pm

I have made this tool so I can check the timing with a stroboscope lamp. The pointer replace one of the screws in the chaincase, you have to remember the cams only runs half the engine speed
Poul
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Re: Distributor Position

Postby Chessiegolf » Tue Jan 14, 2020 5:33 pm

That's an elegant solution. Unfortunately my skills don't run to anything like that, so will have to stick to Malc's method; I'm sure it will suffice.

Thanks for showing us the work though. As you can view the points breaking under dynamic conditions, have you found that the timing wanders around at all, given that all the gearing is very much yesterday's technology?

John

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