Hi Graham,
I haven’t tried it myself but had a quick look in the 1956 reprint of the ’38 – 50 manual – so as a starter, the official numbers are:
Page 23 of the manual states 50 1/2 foot pounds for the main bearing caps
Page 26 states “Fit and tighten cylinder head nuts in the order indicated (see
Drawing 5) (first tightening 3 mkg. (21 1/2 foot pounds), second tightening 5 mkg. (36 foot
pounds). These two tightenings are of great importance, therefore a torsion wrench is
essential. Adhere strictly to the sequence of tightening. Invert the engine. It is an
advantage to use stand MR.3300_20 (see Drawing 17A, fig.1). Check by use of gauge or
comparator 2440-T for any distortion in the bores of the barrels. Distortion must not
exceed 0.03 mm. except in the lower part of barrel, up to 20 mm. from bottom, where 0.05 mm.
is permitted. If distortion exceeds these tolerances, remove cylinder head and replace
lower joints on barrels by thinner ones. Refit cylinder head and check barrels again for
distortion. When correct reading of barrel bores has been obtained, do not touch cylinder
head again.”
Chris
Anonymous