which will probably be the same diameter as 10 inch wheels. You want a 3.44 ratio diff and not a 4.3 as CLIP recommended.

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

HI TK
You have to remember that these blocks have been around for 50 odd years,most of the blocks i get now are all ready out to .040 and .060 over size.
That's why I made the 72.5 mm pistons to give the blocks another life then we have 73mm and then 73.5mm.
I see more 1100S blocks at STD size than the cooper S, but .010 .020 and 030 over size pistons are getting a lot harder to find now,i used to have .020 and 74mm pistons but no body really wanted them, 98% of the 74mm pistons were sold over seas
Graham Russell

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"It's better to be not informed than ill-informed"

Apologies, yes 3.44. My dyslexia rearing it’s head again
My 1275 was out of an auto 1100S. Matt Reed had the mods for the block to make it work. The previous owner had bodgied something up that wasn’t great and could have ruined a good motor. Another reason I was glad I didn’t attempt the engine work myself.

So do I need to change the diff in my mini to work with the auto engine? Whys that

You pick the diff ratio to suit the powerband of the engine and the intended purpose of the car
Small bore engines normally had a 3.76 diff to make use of the less available power
The Cooper S and later cars had 3.44 which brings down the RPM on the highway and makes the gears a bit longer and more useful.

The automatic gearbox had a different diff ratio and drop gears, but you won’t be using them, so just pick the diff ratio like you would for any 1275

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GR we all know how old these blocks are. I was just advising not to jump a few over bores to get to a 1380.

There are plenty of 020, 040 and 060 pistons available surely before getting to a 72.5, 73 or 73.5? Good plug though.

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.