Model 21-25 oil pump parts - For sale

On Ebay. Chance to buy a rare oil pump worm drive gear set and related parts which were originally fitted to a 1926 Model 21 OHV flat tank Norton, but which will fit also the TT Model 25 of the flat tank era. A similar arrengement is used on the early CS1 camshaft models and they may possibly suit this model or be modified to fit.

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.

The Franks redesign of 1931

By Simon

The Franks redesign which resulted in the 1931 range of production Nortons was not an unmitigated success! I have already mentioned my late friend Jack Bindley's experiences with his new '31 ES2. He was as disappointed with the bike as he was with Norton's response to his complaints. Last week I came across a few back numbers of the Beaulieu magazine 'Veteran and Vintage' and found further criticism therein from Richard Chapman, who worked for Eric Fernihough (amongst other well known people) at Brooklands in the thirties. Richard bought a new 1931 Model 18 from dealers in Trowbridge, to which, after careful running-in, he attached a new TT Hughes sidecar. He goes on to say..

"This machine was the slowest thing on wheels and a great disappointment. With the light TT sidecar and a passenger, the maximum speed was about 50 mph and after a while I rode the machine to Birmingham to see the makers about her. A tester took her for a run round the houses and reported that she was up to standard, which drew from me the comment that their standards must be pretty low! After a lot of postal haggling, Nortons gave me a set of what they described as 'dirt track rockers' (ie cam followers) for the crankcase and these improved matters a little. I then got going on my own and raised the compression. I increased the inlet tract bore, fitted a larger inlet valve and a 10TT25 carburettor. This, with stronger valve springs, rebalancing and some work all over the engine, improved matters. The final result was that I could get 80 mph with a passenger in the sidecar, under reasonable conditions."

Richard must have had considerable tuning skills - doubtless enhanced by later experiences with Fernihough.

The reference to Dirt Track Rockers is intriguing as the dirt track model (above) was only made in 1930 - not '31 - and it would be interesting to know just how the rockers differed from the standard profile. And there is a possibility we can find out: a 1930 dirt track engine bottom end has surfaced in NZ and although rather hacked about, I am encouraging the owner to take it apart and see just what is inside! So watch this space!

The decline actually seems to have started with the 1930 enclosed rocker box set-up. The geometry of this rocker box is such that the valves open less than the lift on the cams while with the open rockers they open more...And why did Norton dowtune these engines? My guess is that they were seeking longer term reliability. What else could it be? From a marketing (doubt if the word had been coined then!) point of view it was perhaps no bad thing to have the OHC machines as real flyers and the over the counter bikes as just reliable moderate performance means of transport.