This is a magnesium timing cover to fit SOHC M30/M40 Norton Racing Internationals (pre-war) and pre-Featherbed Manx Norton engines. As with all parts we produce, these castings have been maufactured to be as close as possible to the shape and look of the original castings, and even have the original casting number, in the same position as per original.
The patternmakers I use are excellent, and if I say so myself, the castings are virtually identical in shape and contour to an original - including the inner face and boss. In the second photograph here, you can see an original casting (upper) compared to my version (lower), which demonstrates how close to identical they are. They come with the oil pump drive bearing already pressed in and reamed, and this phosphur bronze bearing has the correct spiral turned oil groove running through it, which stops just before it reach's the outer face - a feature often overlooked, which if allowed to run all the way through, can result in excessive oil being fed into the magneto chain well. It is manufactured in A8 Magnesium Alloy and is substantially lighter than the normal LM25TF aluminium version.
Magnesium inner timing covers are supplied fully chromated (covers are re-chromated after machining to ensure ALL surfaces are protected) - the black chemical finish that protects the base magnesium from corrosion, a necessary precaution as this alloy suffers from oxidisation if left exposed to the atmosphere. They are also lightly sprayed in water repelling (Duck) oil before being placed in sealed bags, to further protect them from condensation in storage, which explains the 'wet' look in the photographs.
Which model specification would these have originally been fitted to?
These would have been fitted to any SOHC Norton fitted with magnesium (M30/40 or Manx) type magnesium crankcase. They would have also been fitted to early pre-Featherbed type DOHC Manx engines. Normal production M30/Manx specification was to magnesium crankcase, magnesium Inner timing cover and aluminium outer cover - however some Works and Works supported engines were fitted with magnesium outer covers (which I can also supply). However these inner covers can also be fitted to aluminium International crankcases if required as the casting is the same (as per my Racing International).
Note: there was only one variety of magnesium cover supplied - the type with no breather hole.