pinion opinion

[Stuart Giles]

Can anyone explain in simpleish terms why it's so bad to mismatch CWPs?

I'll try, but the geometry of gears is not an especially simple subject. The actual shape of the teeth in two CW & P sets may not be the same. Gear teeth have something called a pressure angle as part of their inherent design; this angle needs to match across any pair (or train) of gears. Even if Austin didn't change the geometry of their gears during production, some Austin factory supplied gears were reputedly made by ENV; so unlikely that 'one of each' would make a good pair.  pretty well all spiral bevel gears made at the time (and quite a lot since) are matched after manufacture, in simple terms, oversize pinions are matched to undersize  crownwheels and vice versa. after the pairs are matched up, they were lapped together to ensure a good mesh and silent running.  If you had a load of unpaired CW & Ps in your garage, selecting the ones that give a reasonable 'print'  when assembled and then lapping them together using some fine grinding paste should work. The ideal print (one I did for a mate's Westfield) looks something like this. This print comes from painting a thin coat of  chrome yellow on the pinion. I find it's much more visible than using Engineers Blue.



If you find you're starting off with toe contact on the drive side and heel on the overun side, or the other way round, the gearset is likely to be really noisy and due to the high 'point loading' is unlikely to live for any  length of time.