G80CS Rocker boxes

[mdt-son]

Gents,

G80CS shortstroke engines made 1956-62 had one kind of bare rocker box, p/n 015422, while roadster engines made during these years carried p/n 013958. From then on (1963-66/68) they all used p/n 015422. Externally identical as far as I can tell, and carrying the same casting number (013988),
there must be a difference to the machining of the two (clearance of rockers probably). If someone could shed a light at the difference, I'd be grateful.

As to the innards, the 1956-68 G80CS engine was equipped with rocker shafts (023270) which deviate from those of the roadsters and the trials model (017192). From 1963 on, all heavyweight singles shared rocker shafts 023270. I guess the difference lies in selection of material for the two, and the visual difference will be impossible to spot I guess, unless shafts are marked. Anyone?

For 1956-61, all models shared the same tappet end rocker arms 013948. The following year, the G80CS engine received an inlet rocker arm (tappet side) off the lightweight range (042043) which provided increased valve lift, while for roadsters the factory kept on using p/n 013948. How can we differentiate 013948 and 042043 ?

Another observation is that from 1956 on, the G80CS had a different rocker box cover (015678 vs. 013980 for the roadsters), and this continued to the end. The only difference between them appears to be the finish (015678 was highly polished, while the roadsters had bare castings).

- Knut

[Joker_Bones]

The only one I think I know the answer to is that the lightweight rocker arms are shorter than the heavyweight ones, about an 1/8" IIRC.

[mdt-son]

Thank you J_B. Now we just need the absolute radius of these rockers confirmed.
013948: 1-1/4" (revised)
042043: 1-1/8" (revised)

Anybody?