Napier did eventually accept Bristol assistance over the manufacture of
the sleeves (and the US milling machines that made it possible) - but
only after MAP told 'em to...


IIRC it was the other way round, Bristol did not want to reveal it's
manufacturing secrets to it's competitor, but was forced to do so...

Bristol's secret in successful production of the sleeves was BTW originally
"invented" by accident when a worker ground the final surface of sleeves
with an undressed grinding wheel.