Ignition timing.

[Ianwilko13]

Hi all, should my 1961 Matchless G3 be 1/2" btdc or should it be 7/16"btdc (@ full advance) as I have read both?? Confused, Ian.

[Colonel Blink]

Hi Ian... I'm sure that many more knowledgeable than I can add more, but my understanding is that the 'official' AMC spec is for 1/2" BTDC, but 7/16" is considered more suitable for the characteristics of today's fuels.....

[Ianwilko13]

Thanks for the reply Colin, as I've got the head off I thought that I would get it spot on just not sure which spot, best regards, Ian.

[Duncan]

Hi Ian, the book timing changed at engine number 41575 from 1/2" (39 degrees) to 11/32" (34 degrees) I believe this corresponds with the introduction of the short stroke engine.

Most coil ignition automatic advance/retard units will have some wear in them so I would advise against using the retarded figures quoted and always set at the maximum advance.

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[Ianwilko13]

Hi Duncan & thanks for the reply, this is from Ken Bryant
on servicing the heavyweight singles, and that's what was confusing me?? Kind regards, Ian.

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[Duncan]

Interesting Ken knows his stuff, As you have the head off I would mark the back plate for both 1/2" and 7/16" with permanent marker or paint so that you can decide which one suits your engine best when back together, its a work of moments to loosen the back plate and rotate a little, 1/16" is probably in the margin of error for the stick down the plug hole method. I find B8's a bit cold for normal riding.

[SPRIDDLER]

Don't get paranoid about it. Considering wear and backlash I'm happy to end up with anything between 7/16" and 1/2" on my road-going, softly tuned and long stroke plonkers.
As Duncan said and as far as I'm concerned, setting the timing with a stick down the plug 'ole and a fag paper to within plus or minus 1/16" takes several attempts and is a target rather than an absolute commitment - rather like a politician's manifesto promise.

[Ianwilko13]

Thank.you for the reply, marking the backplate seems a good idea as the head is still off, many thanks, Ian.

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