I have just completed a mechanical service of the PBT on my R-4B, to remove and replace the old, hardened, grease and to polish out some scoring on the cam and pivots). I am about to re-assemble it all, but I have a question.
The cam adjusting screw will affect not only the position of the slug plate, but also the spring pressure on the cam. Small differences in the slug plate position can be mechanicaly compensated by corresponding adjustment of the positions of all four slugs. This means that it is possible to set up the PBT with a range of different spring pressures, no doubt with some effect on the 'feel' of the PBT control and, probably, on the wear on the cam plate and pivots. Does anyone know how Drake did it (eg 'take up the slack on the thin end of the cam, and add one turn of the set screw....'. Otherwise I will take the safe route and keep it 'as is' ! Terry, G3VFO
