Not an immense project, but a very interesting one; the C.12 doesn't really register in the competition records all that much, having really been a solid, worthy, and reliable commuter machine in its day, and precious little else besides,it would seem. The qualities of utter toughness made it an interesting choice for a classic enduro machine, where absolute power is secondary to rideability and reliability.
The combustion chamber design on these engines is allied to the narrow valve angle,being of a bath-tub form rather than a hemispherical one. Inlet-valve shrouding has been relieved by grinding away material from the head, the inlet valve head diameter has been reduced to a less obstructive one, and the valve head faces nicely radiused. Valve spring fitted loads have been set at around 70 lbs, and the rocker spindle springs replaced with phosphor-bronze spacers in the interests of friction reduction.
No attempt to increase the compression ratio has been undertaken at this stage, although it is a viable proposition, but the increase in engine performance from the preliminary steps so far undertaken has been most gratifying. The basic machine package has proven to be effective in competition last year, with a good finish in a Welsh enduro event, ahead of some modern machinery, which was most satisfying. We aim to beat a few more of them next time around with the old chuffer. Riding it through mud has been likened to riding bareback on a crocodile.....
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