Oil Resistent Cork Washer, fits on either side of the rocker arm bearing - Fitting new cork washers helps keep the cambox oiltight - Cork thickness = These are 2.0mm (std) thickness.
Manufactured for RacingVincent by UK based specialist gasket manufacturer.
SOHC Norton Rocker Arms, side plates and cork washer information:
For the duration that the Arthur Carroll SOHC engine was manufactured by Norton's (i.e. approx 1930 - 1957) there were at least 3 different rocker arm variations - possibly more. The initial cambox rockers arms (I think approx 1930 - 33) had a smaller diameter central boss for the rocker arm. The cork washers we sell here are a larger diameter than that earlier diameter - but it is easily possible to trim the cork with sharp scissors to fit the cambox shell recess. The second type of rocker arm had the 'normal' larger diameter, which is the same diameter as these cork washers. This second type of rocker arm used flat shims between the rocker/bearing sides and the cork. We sell that (non lipped) flat shim - item 0288. Not sure of exact periods for this type - but most pre-war cambox's I have seen have this flat shim (non lipped) type.
The final rocker arm type I am aware of is the type that require a 'Lipped' side washer - Item 0287 in our catalog. This type seems the most common. The rocker arm for this type is identifiable by each end of the central rocker arm boss having a lip machined around it, to fit the lipped washer. The diameter of the cork washer for both non-lipped and lipped type rocker arms is the same. Although I cannot be sure - I always assumed the 'lipped' type side washers were introduced because they put side pressure (of the cork) on the rocker arm boss itself, not the bronze bearing inside, as well as helping prevent leakage of oil from the central bearing/rollers.
Because restorers of these engines often end up acquiring mismatched rocker arms and cambox shells, we provide oil resistent cork side washers in three different widths. In the past, I have found the side play of rocker arms to vary by cambox - and therefore a thicker cork washer on some being desirable. A simple way of confirming this is to remove all traces of old cork washer, fit Blu-Tac or plasticine into the cork washer recesses of the cambox shell/rear cover, and then trial assemble the cambox with rockers. Then strip and carefully remove rockers and use a depth gauge to carefully press into the soft plasticine to estimate the ideal thickness of washers required. Dont forget to level out the differences between both sides, and allow a small additional amount for the cork compressing - it is this that stops the leaking!
Cambox Oil Tightness - Assembly Notes:
It is worth noting, it is never particularly easy to fit rockers after new rubbers and corks have been fitted - it is easy to think you are having to overly force everything together. However, if everything is not a tight fit on first assembly - the cambox will quickly start to leak again once the engine has been ran a few miles. Therefore try and trim and assemble the rubbers so it as much pressure as possible is being applied by the rubbers to the rocker surfaces. As an indication - once the cambox is first assembled, the rocker arms should be very difficult to move by hand, feeling almost 'locked' up. If the rocker arms are very still, they will soon loosen up in operation - but this should help ensure the cambox staying oil tight as long as possible. This also applies to the rocker arm side washers (0062/0062b/0062c) - try and fit washers thick enough that some effort is required to fully tighten cambox rear cover (without damaging threads of course). These will also compress a few thou in use - we sell different thicknesses for this purpose.
Final point on SOHC Cambox's leaking oil - after a period of time the top and bottom rubbing surfaces of the rocker arm centre hub (i.e. the area where the nitrile rubbers press against) get worn and sometimes scratched through dirt getting caught. As long as smooth and reasonably evenly worn, the rubbers should still work. However if scoring marks get excessive, even fitting new rubbers will only provide limited improvement. If this is the case with your rocker arms, it may be necessary to have the rubbing areas of the rocker arms lightly milled. There are some specialist Norton engine restorers who will sometimes perform this task, Email us at email@example.com if you think want more information on this.
Update Autumn 2019: New batch of cork washers just manufactured. Apologies for price rise, but I am told that the price of cork has risen considerably since our last batch were made