ffkiwi

The mid to late 50s Cox engines you refer to were DRUM valve-not rear disc-known as the RR-1. Cox's terminology was incorrect. The drum was much smaller in diameter (the major rotating mass)-and machined from steel-so the drive flange which engaged the crankpin could be a lot thinner than a disc valve setup-about 1/32" or so-and the drive was via a hole-but a radial slot from the outer edge also works (and is less stringent on alignment. Being hardened steel and ground the material was a lot less prone to galling and wear than the Valentine disc setup-and the RR-1 engine used a shaft with an extended crankpin having a reduced diameter extension. (see second pic) [this was reasonably common practice on some European engines as well-in some cases the drive pin simply pushed into a hollow crankpin-allowing the same shaft to be used for either FR or RD layouts]
Also-being ground-the fits could be a lot closer and more precise than the aluminium disc used in the current breed of Valentine rear rotary valves. Naturally they (the RR-1) were more expensive than the reed valve coxes to produce-and presumably that was why Cox dropped them. A pity really-as I would take an RR-1 over a Babe Bee any day. Some stuff was just silly-the machined ribbed tank and thev ribbed crankcase nose for example-which was purely for appearance-but must have added significantly to the production cost. Likewise the anodised case which though it presents a nice contrast could have been left plain [though I admit the RR-1 is one of the most visually attractive Coxes made-the other IMHO is the Olympic 15] Cox could have achieved the same visual effect simply by anodising a plain machined Bee tank bell blue...and anodising a standard reed valve case yellow for effectively the same visual effect.



ChrisM
'ffkiwi'