The small tappet oil filter which is so important for the protection of the whole of the upper engine. Note the spring on top of the filter gauze which keeps it pressed against the canister base and stops debris bye-passing the filter.
The speckling inside the canister is surface corrosion - presumably caused by infrequent use and even more infrequent oil changes.
The drillings in the canister lip and lid are asymmetrical to ensure that the parts are assembled correctly.
Note the banjo screws - these are the later variety, with a single hole of 0.075", used to restrict the oil supply to the rocker assembly. See Depot Sheet HD329 of 15/1/37. I intend to convert these to twin holes of 0.156" diameter and have already re-installed a high pressure spring in the primary oil pressure relief valve.
Inside view of the tappet oil filter lid. The inlet is on the left and feeds through the hole, at left of centre, to the outside of the filter gauze. Filtered oil is pumped up through the centre hole and into the rocker assembly.
The two female threads for the banjo screws should have been converted to steel inserts to obviate the risk of stripping during re-assembly. See Depot Sheet HD357 of 4/10/37.
Note that the two upper (outer) mounting holes are 1/8" closer together than the lower pair.
The filter gauze. The bottom is at the bottom of the picture - MAKE SURE THAT YOUR IS INSTALLED PROPERLY !
When I first services my engine this filter had been inserted up-side-down and there was no spring. The oil flowed through the canister without any filtration and pumped dirty oil into all of those tiny rocker drillings. Despite no filtration the gauze was still two-thirds full of sludge. One can understand how the cam followers got into such a state.
Six of the seven camshaft bearings; the rear one (not shown) is a flanged cap. Each bearing is stamped, with its position, on the machined face. Alignment of each half is confirmed by the reference number stamped on their adjacent edges.
The scouring on the wearing surfaces looks far worse than reality and the bearings retain a tight fit on the camshaft journals. Nevertheless, this demonstrates the damage that could be done by dirty oil and incorrect assembly of the tappet oil filter.
The machined step on either side of each bearing mates with a rebate in the casing of the cam follower casings to ensure rigid location.
