|This shape appears to be the earliest and seems to have been used also on the earlier 588 engines, as I have had such a head with the deeper sleeve nut counterbores.
Throughout the production period of the Vintage OHV engines - ie from 1923 to 1930 - Nortons seem to have tried various differing shapes to the cylinder head to barrel joint. Presumably these changes were all aimed at making the joint more gas and oil tight. It seems to be certain that, as produced, the joint shape on head and barrel for any particular engine, whether 588 or 490, was the same. With the passage of time, heads and barrels have been changed for those of different years/joint shapes and this serves to confuse the issue. In addition, by no means all of the 'open rocker' heads seem to have been stamped with the manufacturing date on the inlet rocker standard lug.
I am attaching rubbings of the head to barrel joints from my collected data and against each I have shown comments which I believe to be correct.
|This shape - getting wider - was used on 1928 engines of both capacities (but not ES2s). I have had a head with this joint shape stamped 6/28.
There is yet another subsidiary and unexplained matter worth exploring while we are at it. The 1926/7 and 1929 parts lists show different heads for the 588 engines compared to the 490 engines. Yet the rocker gear, valves, valve springs and inlet stub are all shown as the same. This difference is further confirmed by the sleeve nuts and cylinder head studs - again different items being shown for the 588 engines compared to the 490 version. I have had some of these 588 heads in the past and, indeed, the counterbores which take the sleeve nuts are 1/4" deeper than on the 490 heads and further the sleeve nuts are about 2 1/8" long compared to 1 7/8" on the 490s. There was - apart from these relatively small differences - no other variation to head shape which I could see. No one has yet come up with a feasible explanation for this head difference.
|This one was used on 1929 engines of both capacities and also 1928/9 ES2s. Wider still! The 1930 heads/barrels also had this shape/size of joint face without, of course, the rocker standard cut-outs.
Paul will doubtless notice my lack of comment about overall fin sizes and on this I can only generalise in saying that they certainly got larger as the decade progressed. It would be interesting to know if the head he has with the figure 19 cast into it has the deeper sleeve nut counter bores or not!