Hi, hoping to pick the brains of the M20 gearbox experts out there please ...
I'm building a WM20 gearbox from a collection of mostly used parts.
What amount of side to side play of the selector forks on the gear control shaft is to be expected with new parts? Or what amount is acceptable with used parts as a guide as to whether it's worth fitting them or not?
To reduce excessive side play has anyone tried making new control shaft pins with oversize heads (carbon steel, hardened and tempered)?
I have used examples of both the original small diameter pins/selectors and the post war larger diameter pins/selectors to chose from in the spares bin, but in both cases the amount of side play of the selectors makes me think "no wonder these gearboxes are prone to gear selection issues..."
Thanks, rupert.
The increased radii of the peg tracks and the resulting larger heads of the pegs was intended to smooth out the gear change action so those would be the ones to go for I'd have thought, though obviously both will function OK...Interestingly BSA did the same thing with the engine shock absorber cam profiles....
Track wear is usually uneven as most gearboxes have been incorrectly set up at some point and that tends to result in greater wear at the 'apex' of the bends in the track where it changes direction...Peg clearance to the track is .002"-.006" when new with a recommendation to replace at more than .008"....Ian
Many thanks for those figures Ian, looks like I'll be needing some new replacements...
Agreed the peak in the selector track would appear most prone to wear.
Any witchcraft involved in replacing the pins on the control shaft?
rupert.
The shaft of the peg should measure .740" in length...They have a slight taper and are driven into the shaft...The opposite end to the head then appears to be 'staked' to expand it and lock it in the shaft...
The pegs can be driven out with a hammer and suitable punch...When refitting I use some retaining fit Loctite on the shaft of the peg and then restake the other end as well as I can...The head of the peg must be rested on a piece of shaft and then staked from the other end using a hammer and pointed punch...It's a fiddly job...Also, don't overdo it with the Loctite, if it gets under the selector fork it will lock it to the shaft...I haven't had one come adrift to date and you certainly wouldn't want that to happen...Damaged or more particularly, locked up gearboxes aren't a lot of fun! Russell Motors might be worh a call for new pegs, they have all sorts of small parts hidden away....
If anyone has developed a better/easier procedure for replacement I'd be interested to hear about it!....Ian
