SOHC Cambox rubber pad set, cut/planed from hard wearing oil resistent rubber (Nitrile), to the same width and thickness as originals, these are fitted both above and below the rocker arm central boss in all SOHC cambox’s.
Along with the cork side washers, it is these being worn that normally results in these cambox’s leaking badly. An original single piece rubber pad (new old stock from the 1940’s I believe, I bought some many years ago from that great Norton exponent Phil Heath) was used as a template to ensure the correct width. This original type was supplied longer because each one was cut into two, i.e.one rubber for each rocker arm. As shown in the 1948 catalog, I supply two separate ones of similar length, both of which are slightly longer than required, which can be carefully trimmed to your required depth. (They should be trimmed so they protrude just proud of the cambox slot, so the rocker arm has to be forced – carefully, into the cambox). The smooth end should be abutting the rocker boss and your trimmed end opposite.
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 firstname.lastname@example.org if you think want more information on this.