Cooper Tune, 2nd motor build (from Rover unit for Japanese market) has new, standard OEM pistons 35 thou down the bore as you have found.

My 1293 build has 20 over pistons that must be 30 years old but the engine never ran (chap who built the engine, now deceased, was going to go racing but his brother said "I don't think they ever got the engine to run.")  They are 13 thou down the bore and I need to true up the block to take care of 3-4 thou variance on face.  So having done that perhaps I'm good.

Interesting story, the 'old' power unit was from a badly rotted Cooper shell.  When I was offered the bits, the power unit looked awful, had been sitting outside for years...dirty, rusty etc.  I said I'd come back for the power unit as I trailered the old shell away in the rain.

Long story short, when I unbolted the head I was looking at shiny piston crowns & bores with honing that looked as fresh as yesterday.  When I split the block, I was looking at all brand new gears...nothing internal to the engine or tranny showed any evidence of all the years the engine sat outside.

The 1293 is being built on that old Austin America block.  It will go over the OZ tranny that will be rebuilt and have 3.44:1 Fd.

What piston to deck are you getting on your dry build? The last few 1275 to 1293 builds I have done have used Mega pistons and they are running .032 to .034 down the bore of A+ block dry build. When you bring them up to zero combustion chamber size on a std 940 head makes for to much compression. You need to cc your head, figure gasket, dish and above ring. Once you know what you need in block, surface block to get there. In recent contact with Nick Swift and Calver they are running .020 down to get compression desired. I have always run zero deck on race engines as it reduces detonation. On street engines I leave them .005 down. As far as stretch and crank flex Dave Tabor ( who sponsored my vintage car ) working with SCCA 948 national cars found he could run the pistons up out of block and needed .017 between piston and head for stretch and flex. This was in engines running 8000+ RPM. My car which I drove to Mid Ohio has and old race Cooper S block which after boring to 73mm required machining pistons to get them back in the block at zero. That reduced dish and even working the chambers I required a custom Cometic gasket to get to 9.5 to 1. Figuring it would be the last engine I'd build for my street cat I backed off my normal 10.2 spec due to fuels now and in the future. It runs fine on mid grade fuel. I have run for extended periods at 90 mph with no ill effect. Don't know if that's what you are looking for but there it is. Steve (CTR)

PS Calver is busy I recieved a cyl head from him last month. 

Pistons .010" down to flush is fine for a road motor.
Leaving more down just adds to chamber volume and reduces squish.

[edit]Don't forget, you have .030" or more head gasket thickness. Pistons ain't gonna hit da head..!

  ya know hunt.....i never really thought about that factor...

     where is our keith calivar at ??    or i know Don would know ... " live help " ..

      please keep me posted on this....will ya ????

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Connecting rod stretch...what do engine builders consider when decking the block?  I am using new A+ rods & new A+ crank for 1293 build.  SW5 cam, standard valves...not a road burner.

If I true up the block (taking minimum off for 3-4 thou measured variation), should I leave 10 thou for stretch?

(I have 0.0015" clearance on big ends using new A+ rods/crank)