Rocker shaft question

[mikedsilva]

Do the shafts that the rockers "rock" on, ever wear out?

I believe that the bushing in the rocker itself, is bronze? and hence softer than the rocker shaft... is it possible for the shafts to ever wear beyond spec?

And if so, what is the minimum diameter for a rocker shaft, before I have to throw it away...
thanks in advance....

[Optimusglen]

Rookie here, but here's my take.

Neither the shaft nor the rocker fully rotate, so any wear is limited to one side of the circumference. On my engine these pivots are not directly oil fed, so the majority of the joints lubrication is done by the material properties. This also lessens the chance of debris making it's way to the bearing surfaces. The wear that does occur can be adjusted out when you do a valve adjustment. Is there a spec and a wear limit? I would assume so, but I couldn't tell you where to find it if it's not in Wayne's book.

[chris_seven]

Shafts can wear and if they are not installed correctly they can also fail.

If the shaft 'walks' in the cam housing the shaft can be loaded incorrectly and they will fail from the bottom of the slot.

I think you can describe the lubrication as 'mixed mode' at best.

The wear limits quoted by Porsche concern shaft and rocker clearance with the limit being 0.060mm.



Porsche Motorsport used to offer 'Surface Treated' Rocker Shafts to use with the 906 Style Rockers used on all Porsche Race engines up to the 935 but they have been NLA for years.

As part of the development of new Forged Rocker Arms we started producing similar shafts a few years ago.

These shafts are manufactured using a 300MVAR Steel and have been hardened to around 42HRC and then surface treated using a Nitrotec Process which produces a surface hardness of around 1000HV with much lower levels of friction than a hard chrome plated layer.

The shafts have been precision ground to a very close tolerance to an Ra of around 0.5microns which is recommended for use with the Bi-metallic bearings used in the 911 rocker arm as this surface finish will retain an oil film and improve the lubrication of the bearing.