This is the distincive magnesium cambox cover fitted to racing SOHC camobox's, which allow for the central oil feed to the camshaft.
These were fitted to the racing (magnesium) cambox's used on competition Inter's and Manx's from the early 1930's through to the introduction of the DOHC. This type of cover were also often fitted to the later (Featherbed) Inter models.
As always with the castings I have made - I have had patterns made using an original Norton casting to copy from, and as you can see from the photograph, they are indistinguishable from an original. These castings are cast in high quality magnesium alloy and come fully chromated (and as you can see from the photographs, sprayed in Duck Oil to protect them from corrosion in storage), and if you are intending to fit our cambox oil feed jet boss, I can also fit this for you before sending out - as per the top photograph. This listing is for the bare casting, but all other parts required for the central oil quill feed are also available in this section.
Oil Feed to SOHC Cambox - Background:
For those who may not be familiar with the history of the Carroll designed SOHC engine: As standard the SOHC cambox was fed with oil from the crankcase - coming from an oil gallery that went to a union at the rear/top of the crankcase. This also had a feed to the barrel walls, for lubricating the piston. There is an adjuster in that engine bolt to regulate the amount of oil going to the barrel (which does not affect the cambox feed - which is often misunderstood).
However, the standard 'roadgoing' model fed the oil into the cambox cam chamber through the top oilway boss - where it is fed along the outside of camshaft, through a slot on the cambshaft spacer, designed for this purpose. This seemed to work reasonably well, although it is not uncommon to find the spacer has serious score marks along its outside surface, which may reduce efficiency.
Very soon in the evolution of this engine (i.e. early 1930's) the competition version of this engine was modified to employ an oil feed directly through the centre of the camshaft, out through oiling holes in lobe of the cams, and from there into the cambox cam chamber. This direct feed ensured a forced feed of oil directly onto the cam lobes - which due to the more extreme lift of these SOHC sports/racing engines are prone to heavy wear.
To enable this 'central' feed, a second (lower) boss was adopted in the cambox, which had a seperate oil gallery through to the bevel cover, where the oil was then routed through a bronze quill into the camshaft. The same design of quill was already employed in the BigEnd (on all Norton single models) - but it is important to note these quills are NOT interchangeable, the hole in the BigEnd quill is much bigger than the camshaft quill . . . and getting them the wrong way round can result in either over oiling the cambox or (far worse) - possible damage to the BigEnd.
The first competition cambox's to adopt this central oil feed were aluminium cambox's. By the mid 1930's, Norton had introduced magnesium alloy cambox shell's and bevel cover's for it's competition models, and from that point onwards - only the competition magneisum cambox type had central oil feed to the cam's. However both types of central oil feed cambox are easily identified because they all have a quill nut in centre of the bevel cover - as per the cover shown here.
It is also worth noting that most (all?) Featherbed roadgoing Norton International models seem to have had engines built using the magnesium cambox and central oil feed. Although not entirely sure on the reason for this - the story I had heard most likely was, that by the early/mid 1950's Norton had stopped using the SOHC cambox for racing, and had gone over to the DOHC type. Therefore they had stocks of racing magnesium cambox's still available - so used them up on the Featherbed roadgoing models! This is almost certainly true as money was always tight, but it would also have offered better oiling for these engines.
As a final note - providing your aluminium cambox has the second (lower) boss in place, it is possible to retrospectively change your non-central feed alloy cambox to centre feed. I did this to my own Racing International when I first raced it, as did not have a magnesium cambox at the time. However, it is not a job to be taken lightly - it requires the blank lower boss boring and threading 1/4BSP. Very carefully machining oilways in the cambox to come out in the bevel cover mating surface - to correspond to this cover. Then the fitting of a centrally fed camshaft/quill/and this cover . . . and to ensure your cams have holes in them for central feed. Finally, you then fit a blanking plug into the original top feed. This is a lot of work, but does result in better oiling to the cams - and obviously makes your Inter cambox look like an M30/early Manx!