Were single cylinder motor cases painted?

A friend of mine who has worked on quite a few Norton International and Manx bikes from the 1940s and 50s has found silver paint on many of their crankcases. It is also fairly easy to find photographs of Norton Manx racers from the 1940s and 50s with silver paint on their magnesium crankcases.

To back up Ben's comments - Yes, I think is the answer here with regards to the OHC models. I have two sets of International crankcases â one of which I know has not been touched since the fifties and they have both been painted silver. One has a âgoldâ sheen to it although this may be due to staining. Possibly, the reason for painting alloy cases was just cosmetic or maybe it made them easier to keep clean.

Manx Nortons from 1948 to possibly 1950 had painted crankcases â whether they were chromated underneath I donât know. A look through the Keig collection of TT photographs shows this quite clearly on unmodified bikes. There is even one picture of a new featherbed Manx with painted cases. It has been argued that they could have been un-chromated bare mag-alloy but it corrodes so quickly I canât see this being the case. Also, I have a book, written in the late 40s, in which Francis Beart recommends âremoving all paint from the crankcasesâ when preparing a Manx.

Strangely enough, most cam-boxes, but certainly not all, were unpainted.

The only reason I can think of â apart for cosmetic reasons or maybe further anti-corrosion measures â is the shortage of di-Chromate salts (used in chroming as well as chromating) immediately after the war. Maybe the 47 Manxes used pre-war stock chromated cases as I canât find a single photo of one with painted cases. The 1948 350 Manxes used a different crankcase so pre-war stock wasnât an option.

My own 48 350 Manx had painted crankcases and chromated, un-painted cambox. The attached photo is of the bike, lined up for TT practice, only 3 weeks old (and having already raced in the Leinster 200) so itâs doubtful that it would have been done by the owner â T L Irwin â in that time. (Note how much brighter the finish on the cases is compared to the gearbox). When Iâve finished restoring it will have painted crankcases which will no doubt raise a few eyebrows!

Regards.

Ian.

Forgot to add that my comments aboverefer to PRODUCTION Manx Nortons!

Ian.

I can't think of a logical reason to paint cases on a racer, unless the castings were so poor that they needed it, or they wanted to replicate a finish used on works Mag-alloy??.

I guess there must have been some reason - incidentally Matchless G50s and AJS 7Rs has their mag-alloy cases painted gold, my Rickman Metisse mag-alloy hubs are also both chromated and painted. Magnesium-alloy bodied magnetoes were usually painted too as were mag-alloy hubs and brake plates. Perhaps it was just to add that little bit more protection. Maybe Norton stopped paintingcrankcases later because they didn't expect them to last long enough to warrant the extra protection/expense?!?!

Of course, none of thisanswers the question as to why 'ordinary' alloy International cases were painted!?!?

Regards.

Ian.