Trial fitted the new laygear to a 4 synchro remote box using the old thrust washers.
Clearance was .009 inch but should be under 0.006 inch. I found a thicker thrust washer in a box of bits but it has closed the clearance down to 0.0015 inch when the manual has the the minimum as 0.002 inch.
The laygear spins freely and there is a slight amount of end float. BUT is 0.0015 inch too tight once the gearbox heats up?

Should I linish the back of the thrust washer to be safe?

Yes, I would take a little off the back.
I know idler gear clearance reduces when hot, this might do the same.
Edit:
A friend built a rodchange box with only 1.5 thou idler clearance, he had trouble changing gears when hot.
So I gave it 2 thou more clearance and it was fine.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I would have thought the aluminium box would expand faster and more than the steel laygear, therefore providing the clearance you need.
I rebuilt a Range Rover gearbox many years ago and was told by the JRA staff to build it with the minimum clearances I could so long as it was not “tight”.
I followed their advice and finished up with the quietest RR gearbox I had ever heard.

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Find a job you love and you will never have to go to work !

Thanks for the comments.
It sounds like there isn't a lot in it between clearing and binding, especially when the stated minimum is only 2 thou.
I have linished the back of the washer and now have a close 3 thou, so that should be correct.

As an afterthought, could I have fitted a packing shim behind one of the 2 thrust washers to close down the excess clearance?
Or would that be something else to break off and float around?

I’ve noticed guessworks in the UK makes the shims, so could be another option if you don’t have the correct thrust washers

Eg
http://www.guess-works.com/Shop/Parts/d ... htm?id=561

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I happened across one of their websites a few days ago. They are sourcing some very useful NLA items. Didn't see any thrust washers, though.
Thanks for the link. When I google "guessworks" I keep getting "leather handbags" and other fashion accessories.

Shims from Guessworks. I had 11thou clearance, so I'll go with 3thou clearance (with the option of 5). Better to go for the lower end of of 2-6thou ??

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1970 Mk2 Cooper S under restoration

I rub the bearing face on a sheet of 1200 grit emery, just sprayed with wd40 - it cleans the face up nicely and is easy to take off a thou or few when needed

a lot of years ago I bought a very flat glass tile for doing stuff like this, very handy

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did I tell you that I won a trophy?

Same, but I used to make creams and ointments on it (pharmacist). Now, re-purposed

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1970 Mk2 Cooper S under restoration

good for mixing body filler too, right?

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did I tell you that I won a trophy?