Fully Advanced Ignition timing

[SørenMortensen]

Hello Ariel People

what is the Fully Advanced Ignition timing

for my Ariel SB31 550CCM side valve i have found it should be 9,5mm but im not sure about it

kind regards

Søren Mortensen

[Roger Gwynn]

The owner's guide is available free to members on the club website, you will find this information and much other useful stuff. The figure is 7/16" but is not critical.

[SørenMortensen]

Thanks Roger

we have started with 14,5 mm then reduce it to 9,5mm and thats not far from 7/16 11,11 mm

[cmfalco]

The figure is 7/16" but is not critical.

+1. Old manuals give timing specs to the nearest 1/16", often 7/16" (11.1125 mm) or 3/8" (9.5250 mm) for most engines. Although the piston position depends on both the connecting rod length and stroke, at the BTDC timing of the engines we care about, a resolution of 1/16" (1.59 mm) is equivalent to a timing difference of nearly 3°. I find it isn't too difficult to set the timing to ~0.5 mm using a ruler in the spark plug hole, which is a bit better than 1°. Given that we seldom even know to 1° (or even 2°) what the "correct" value should be for modern fuel in a given engine, it's probably not worth obsessing over tenths of a mm.

[SørenMortensen]

thanks cmfalco

so if im between 9.5 and 11.11 then it should be all good