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OHC Cambox single knocker



I am building a 500c OHC engine from parts.

The cambox which I intended to use is in great condition but it was fitted with smaller diameter rockers ( the pivot area where the cork washer goes.) Can anyone identify which year or engine this was fitted to and are there any rockers available?


Thanks Philip



Via email.  Is there any other dimensional difference?  what are you comparing against?





Yes I have a cambox which appears to me to be the most common one ant the cover screw holes are in different position


According to the notes by the late George Cohen, the earliest engines (1931, 1932) had rockers with smaller bosses than the rest.  The cambox also had smaller fixing bolt centres.  Does your cambox fit your head?

The other change I don't understand is that the steel washers on each side of the rocker bosses also changed from flat washers to washers with a shallow cup, or rim, to contain the corks.  Can someone explain? Were the cambox recesses a bit larger diameter?  And is that why your rockers appear to be a bit small, and what you need might only be new cup washers?


George's notes say the earlier camboxes had the four mounting holes at 2 1/8" square centres.  From mid 1931 they changed to 2 1/4". Richard writes below...3 1/8 and 3 1/4.  My excuse is copying a mistake in George's notes...and not taking out my ruler..


Hi Philip,

   As David says, this sounds like one of the first Carrol OHC cambox, made only from 1930 to '31. The engine was redesigned as the International for September 1931 with the down-draught cylinder head. The stud centres for the CS1 are 3.125 inches and the Inter is 3.25 inches. The CS1 became the touring version at the same time and shared many parts with the Inter including the stud centres.


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