Rocker Box

[assessor]

I have an 1950 G80S with an aluminimum rocker box. I noticed that it has a vertical split near one of the boltholes probably caused by overtightening.. I could probably repair this as it does not leak but I am wondering if this should be aluminium or iron for the year as I may as well replace it with the correct one if it is iron. Can anyone advise please? Also should this model have a alumininium or iron head as the head on mine is ali.

[SPRIDDLER]

I think you'll find that rocker box covers were always aluminium.
I'd be surprised if tightening the rocker cover bolts has cracked the cover - it could have, but usually the 5/16 BSF threads in the ali head strip first as a result of excessive tightening to try to cure an oil leak between cover and head. 10 to 12 ft/lbs is plenty (i.e a short ring spanner, not a socket and a ruddy great bar!). (Added later) - Also make sure that these tapped 5/16 holes in the head are clean as gunge at the bottom of the 'oles will cause the studs to feel tight before they have applied sufficient compression to the gasket - thus allowing oil to leak from the joint.
According to Roy Bacon's reference book the ali head was introduced for the '51 model.
The new models were introduced when the factory started up again after annual factory (August) shutdown, therefore a machine made and also registered between Sept and Dec '50 could have the spec'n of a '51 model (i.e iron head changed to ali). It may of course have merely been fitted with a later replacement head at some time.
Edited by - SPRIDDLER on 01 May 2009 3:31:18 PM