Magneto pinion backlash

[morven21]

Can anyone advise as to how much backlash there should be between mag an idler pinion on M21? I assume that a pinion tooth should not quite touch the trough between two teeth of corresponding pinion, correct?

[Rog1]

I think that's correct. It's what happens on my M33; I know it's not quite the same bottom end as your M21 but the general design is the same.

[morven21]

Thanks, Rog. I think all gears go on same principle.

[Dean Southall]

The M20 manual does not give a value for the backlash on the mag pinion but advises there should be some clearance to avoid whine (and I assume load on bearings/bushes).

[morven21]

Yes, i looked, it just aid as you say. I have shimmed it so that mag pinion slides onto it's shaft easily, without touching anything. See how it runs.

[Ian C]

A4 paper is approx 0.004" thick, so I fit a strip between the mag and idler pinions then nip down the mag, then adjust shimming accordingly. Paper strip should run through without being too badly wragged when you turn engine over.