I have just bought a new pin drive S pump, it felt like the shaft/inner rotor had a lot of clearance when checked by hand.
So, I bolted it together and put a dial gauge on it. There is .005" end clearance there, which to me seems a lot for a new pump (pumps lose oil pressure when the rotors have worn the end cover).
I am going to strip it and face the body to give max .002" end clearance, anybody care to comment?

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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'll be doing one in the morning or later this afternood, I'll let you know how it goes... can I ask what brand of fuel pump it is or where you got it?

Factory docs say reject at 7 thou

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

I took it apart, clocked the face up in the lathe and faced .003" off the body. It feels much better now with .002" end clearance.
Pump has had an Oz made S shaft put in it, but I wonder where the pump was made...;-/

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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 like to know as well Kev may save me buying sub standard parts

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" A Hundred Years From Now It will not Matter what my Bank Acount Was,
The Sort Of House I Lived in, Or The Kind Of Car I drove ... But The World May Be A Better Place
Because I was Once Important In The Life Of A Child"

Just out of interest, I checked my new A+ slot drive pump from Minispares UK, GLP138.

0.0025" - 0.003" end clearance. 0.0025" feeler gauge slid in easily & the 0.003" feeler gauge was too tight!

Cheers Shane

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If it's not a Cooper S, the mini was designed to be modified!

I used to find this problem allot a few years ago, mostly with pin drive small bore pumps.
One brand new pump had enough clearance that it bleed down after initial startup and would not build oil pressure again unless primed.
I have had to do the same as drmini numerous times to get the clearances right.
I now check each pump I fit, but haven't had a problem for a while now.
Once faced and the clearance set they have been completely trouble free.

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How can it be rusty when it's covered in so much oil?

What's the proper method for facing them? Can this be done at home without machine tools with any success? (perhaps on oiled emery over a piece of glass??)

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

The first few I did were oiled emery on glass method. Just go carefully in a fig 8 and turn regularly.
These all worked perfect.
One engine in a daily driver so far has done over 100,000km, no problems and holds good oil pressure.

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How can it be rusty when it's covered in so much oil?

Glass is OK but is not always flat, particularly these days. If you can find something that has a flat machined surface that is better.

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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.