Well I have finally got the M20's engine running like a top so naturally the gearbox has now failed.
It will not select 3rd on the way up.
I have pulled the box out but can see nothing wrong other than a worn pinion sleeve bush and a lot of lateral movement in the quadrant shaft.

I know the bush is knackered but have no idea how much movement is allowed in the quadrant and can not remember how much there was in there 8 years ( about 40,000 miles ) ago when I last had it apart while doing rings & resleeving the barrel.
So before I go doing silly things any one know what the specs are ?
Bike Beesa
Trevor

email (option): bsansw@tpg.com.au

Hi Trevor.
Just to be clear, when you say selector quadrant do you mean the shaft that the control rod attaches to or the selector shaft? If it's the quadrant then a fair bit of play wont affect gear selection, if it's the selector shaft then aim for .005" end float. The main and lay shafts should also have .005" end float.
Check for wear on the selector forks and the groove in the selector dogs also check that both selector dogs sit equal distance between their respective gears when in neutral if not the shafts will need to be shimmed to align the selectors.
Lastly use the search function, there is lots of info on gearbox set up.
Let us know how you get on.

email (option): spacemonkeym@gmail.com

Thanks Matty

It is the small shaft that turns the selector shaft.
The one that is connected to the ratchet plate by the adjustable arm.
I have done a search on gearboxes but most of what I found I already knew.
If I hold this shaft pushed into the box then I can select all gears easily with a small spanner turning the square end.
If I pull it out as far as I can ( about 3/16" ) then it wont change .
ASAIK this shaft simply meshes with a cog on the selector shaft so it should not be affecting the gear changing.
I am assuming that the top hat bush inside the box has collapsed so what I wanted to know is roughly how much end float.
3/16" seems to be a lot to me & I can not remember what there was the last time I was in the box

email (option): bsansw@tpg.com.au

Hi Trevor..It is unlikely the (steel) bush that the selector quadrant shaft runs in has collapsed. Have you refitted the little 'top hat' shaped spacer that fits over the shaft (outside the inner cover) before the link arm is fitted?...Ian

Thanks Ian.
Yes it is there so it looks like the problem is deeper in the box so it is on with the diving suit and down I go.
I was hoping it would be some thing simple & easy but that looks unlikley now.
Bike Beesa
Trevor

email (option): bsansw@tpg.com.au