I remember reading CC's autobiography about 40 years ago. When he wanted a Differential ratio between two ratios that were available, he forced together the pinion of one with the crownwheel of the other, and ran it in on Brasso(abrasive polish.) This was in the early days of Lotus 7s when he built 'specials,' as they were called.

Strange what sticks in your head.

Generally nothing useful.