1930 valve lifts

By Simon

Regarding a previous blog on the Franks redesign of 1931, hereby some calculations on valve lifts; I freely admit I have not actually measured the lift of a valve in an assembled engine to see if the results achieved by calculations based on the measurements are - more or less - correct and perhaps someone should do so! Anyway, the details noted are:

Open push rod engines (1926 - 1929). Cam followers - contact point with cam 1.63" inches from pivot point; contact with tappet foot 2.037" from pivot point. Thus cam lift is magnified by a factor of 1.249. Rockers - centre of ball end to centre of pivot point 1.329"; centre of pivot point to centre of contact point with valve stem 1.476". Thus tappet lift is magnified by a factor of 1.11. Average cam lift on W7 inlet cam (they all seem to vary a bit) 0.290" so lift at valve is 0,290 x 1.249 x 1.11 = 0.402".

Closed push rod 1930 engines with standard cams (NB; not ES2 cams which have higher lift). Cam followers - contact point with cam 1.87" from pivot point; contact with centre of push rod socket 2.193" from pivot point. Thus cam lift is magnified by a factor of 1.172. Rockers in cast alloy rocker box - centre of ball end to centre of pivot point 1.528"; centre of pivot point to centre of contact point with valve stem 1.5". Thus push rod lift is actually very slightly reduced by a factor of 0.981. Average cam lift on 1930 cams 0.300 inches so lift on valve is 0.300 x 1.172 x 0.981 = 0.345".

The 1930 ES2 cams (marked E2720 and 2721) have substantially greater lift than the 1930 Model 18 type and have the same small base circle. The lift is 0.343" and use of these cams in a 1930 engine will increase the valve lift from 0.345" to 0.394".

I find it interesting that even with the sporty ES2 cams, valve lift on the 1930 engines does not quite match that of the earlier open push rod/W7 engines and there is such a big difference between valve lifts using the standard 1930 cams and the earlier set-up.