This is an aluminium timing cover to fit SOHC Norton International, CS1 and pre-Featherbed Manx Norton engines - that were originally fitted without a breather hole (see also item 0318b for covers with breather holes). 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. 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 LM25TF Aluminium.
It should be noted that when ordering an Aluminium timing cover, these came in two standard types: Very early and very late covers were devoid of a breather hole (as per all magnesium timng covers), but for a period around the mid 30's to late 1940's (I think!), they had a breathing hole at the upper part of the bevel chamber.
This listing is for an aluminium timing cover WITHOUT breather hole.
Aluminium covers are supplied with the visible areas polished (but due to the intricate shape, I have refrained from obtaining an overpolished mirror finish, to avoid the increased risk of damaging the machined faces).
Note: After initial machining of this batch of timing covers it was found that with the variation in different original outer covers over the years, somes did not line up well. Therefore, the top threaded hole of the covers was bored out to take an oversize threaded insert, and then the 1/4 BSW" thread hole re-machined in a slightly different position, to make the fit more 'generic'. This insert has been expertly applied and is virtually invisible. It in no-way reduces strengh (in fact it makes the thread stronger, as it is of a higher tensile strength than the original casting material!), but it is mentioned for completeness.
The final photograph in this item shows an Inner Timing Cover, matched with an Outer Timing Cover - Sold Seperately