Barrie
The Weller Engine was for the period very advanced, there were quite a number of changes relating to the camshaft drive & clearly in the PVT era lubrication of the main bearings, The most restrictive part of the engine was the low fundamental crankshaft resonance which restricted the ability to safely rev over about 4500 RPM, however as we know it made up for it with the torque & lightness of the engine.
It is disappointing that little was done to overcome the crankshaft resonance issues which were well know back in 1907 when Rolls experienced crankshaft failure on the six cylinder engines, six cylinder engines all suffer from resonance issues & the third harmonic, Rolls overcame this with there friction crankshaft damper which was positioned in the crankcase at the front of the engine. I believe other engine makes such as Riley also used this solution!
AC came up with the damped flywheel which is questionable & in the Post War period the front bonded disk damper, this mainly i believe was to deal with the fundamental crankshaft resonance, but it is doubtful if it had any effects on the harmonics, unfortunately these bonded dampers also deteriorated with age & exposure.
As we know the CL version of the engine basically specified the thin wall bearings & increased the main journal size marginally, this was a clear improvement over the thick wall white metal bearings as they are able to handle higher loads as the bearing bond stress was reduced.
The unfortunate thing was not to take the opportunity to specify even larger journals Main & Big end so a stiffer & higher resonance crankshaft could be designed so allowing the engine to Rev safely & more freely above 4500 RPM, this would have allowed the Weller engine to be more competitive against the much developed BMW/Bristol engine.
The other aggravating issue was the wet liner sealing which became much more difficult when Asbestos was banned, a key cause if leaking has been the movement of the liners particularly at the lower liner seal, a key requirement is the ensure the liners are not allowed to move once installed as the water seal can be broken!
The engine is well thought of by quite a few people & is used extensively in GN &Frazer Nash cars in competition.
The engine design still has good potential, obviously in older series cars!