I have been spending a considerable amount of time analyzing the rocker shaft/ cam housing issue.
We had tooling made to bore 47mm housings to 49mm to alleviate the supply issue and now loose rocker shafts are the challenge.
In evaluating the issue it seems that by over-tightening the steel rocker shafts, the bore in the cam housings were expanded by anything from .0005" to 1.5" and beyond. This excludes damage like gouging.
We started with a new rocker shaft and installed the bolt, nut and sleeve on the bench and tightened it to 160 inch/lb. We measured an expansion of .0015".
A quick inspection suggested that the nut and sleeve would bottom out in the rocker shaft as you increased the torque.
We determined that by machining the nut and sleeve you could increase the expansion of the rocker shaft to .0025". In the housings we tested, this very slight increase in expansion was enough to secure the shaft in an over sized housing. YMMV
Shaft depth 7.00-7.03mm.
Standard nut 8.24mm ...machined nut 7.9mm
Standard sleeve 8.04mm ...machined sleeve 7.0
Please forgive the crude machining...this was only a test.
Heads up on new rocker shafts: The Febi rocker shafts have a slot smaller than the OE Mahle shafts that makes using RSR seals almost impossible.