I recently purchased a M20 gearbox for my project. Yesterday I decided to remove the outer cover to look inside this gearbox described as "good".
Though the quadrant isn't in too bad a condition it has some cotter pin damage and shaft unevenness.
One oddity about it, is that it has a bronze bush that bares onto the gearbox bush. Both worn.
Reading on the forum it seems there is no end support bearing?

So questions.
Would it be better to make a quadrant that bares onto the gearbox bush? The quadrant would just have a "finished" bore to be supported by the bronze bush.
Is the tooth form of the quadrant 12/14DP 20PA ??
Would rounding the edges that hold the spring be better?

The next horror was the quadrant bush being glued with mastic into the outer cover.
I read that that the bushes were hardened and ground, would a tough steel unhardened bush be ok? This is what we use on many other engines.
If so it might be possible to machine an o-ring groove in it's outer edge to take a 2mm section o-ring, thus keeping dirt out and oil in.

More questions.
Does anyone have the outside diameter of the kickstart bush? I see Ian has kindly posted many other dimensions.
I imaging that my casting is worn. There is not enough material to allow a liner. Would it be an idea to make these bushes in oversize's?
What is the interference fit for this bush?

I'm sure many more worms will reveal themselves as I dig deeper.

email (option): pes.sales@btconnect.com

The kickstart quadrant where it fits into the bush should have an O.D of 1.1855" - 1.1865"...The clearance between the quadrant and the bush should be .0005" - .0025"...

The quadrant is entirely supported by the steel bush..I have seen bushes fitted in the back but that's not a standard feature...
Rounding off the edges of the quadrant where the 'hook' of the kickstart spring fits may be beneficial though I don't recall seeing a spring broken there..They usually fail in the spring windings themselves (and even that is a rare occurrence)...Interestingly, the small screw that retains the other end of the kickstart spring through the 'eye' of the spring and the outer cover was also hardened as standard...

I don't have the outside diameter of the kickstart bush but I'll measure one later today...I should think an interference fit of .001"- .002" in the cover would be OK with the cover being heated to fit the bush...Ian

email (option): ian@wright52.plus.com

I measured 3 NOS bushes and they all have an O.D of 1.438"...Ian

email (option): ian@wright52.plus.com

Thanks Ian.

email (option): pes.sales@btconnect.com

I ran a few of these with an O-ring groove. Available in over-sizes too.

email (option): pes.sales@btconnect.com