AJS 16M 1951

[R]

We are assuming there is nothing untoward going on here,
like a case full of broken teeth jamming up the works. !
Without a full inspection, its a bit of a lottery if this will be good.

Draining the oil and inspecting what comes out is a useful diagnostic tool.
If its nice and clean (and new) it can go back in ?

[john.k]

Pull the gearbox to bits .....the whole joy of old bikes is pulling them to bits and putting them back together again.

[dynamic]

small metal fragments found in g/box oil so an inspection will be the next move

[john.k]

The CP Burman boxes dont normally chip gears ,as the gears are quite soft to avoid breakage ........the worst can happen is tooth breakage caused by worn layshaft bushes..........good news is millions of these boxes were made in WW2 ,and NOS parts are cheaply available .........be aware though there are several changes in the whole gearset made in WW2 to meet criticism of too wide gaps in the ratios............In general ,there are prewar trials ratios,post war trials ratios,and standard road gears.

[Rex]

Or is it timed on the compression stroke?

[john.k]

Most likely cause of jamming is burred first tooth on the starter quadrant .......first meshing tooth should have a sharp point .....when it gets burred ,the traditional cure was to grind it off and sharpen the next tooth...........ditto the mainshaft ratchet gear ...it should have pointed teeth ..........I d also add ,you never stab at the pedal,mesh the gears first before applying pressure ...........The 1956 on  AMC box has the Norton style kickstart with a sprag engaging an internal rack ......reliable and near abuse proof.

[dynamic]

thanks all for posting I will update on prognosis