This is an aluminium timing cover to fit SOHC Norton International, CS1 and pre-Featherbed Manx Norton engines, of the type originally fitted with a breather hole.
As standard the inner timing cases have been machined without the breather hole. However, I include a picture of an original timing cover inset to the main cover, that has this additional breather hole. If this catalog item is ordered then I have a jig to ensure the hole is machined into the correct position. If ordering this version of the Inner Timing Cover please bear in mind there may be a two week delay to allow for the cover to have the additional hole machined.
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 item is for a timing case WITH breather hole. Note - when ordering this item, there may be a delay of two weeks, to allow me to machine the additional breather hole into the cover. 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