Rocker Shafts

[chris_seven]

It has always surprised me that many people seem to build competition engines using refurbished rockers and rocker shafts.

The idea of polishing or as shown in a recent U Tube clip treating a rocker shaft with a stone just doesn't appeal.

If you reduce the diameter of the ends of the shafts by polishing the fit into the cam carrier will be affected and make them more prone to leaks or 'walking'.

Stoning the rubbing face that contacts the bush will affect roundness and I am not convinced this is a good idea.

As we have manufactured forged adjustable rockers and as we have just ordered the dies for the '906' style rocker it seemed a good idea to reproduce some rocker shafts which would have good wear resistance.

I believe that RSR Rocker Shafts were surface treated and had a Black Finish and were also expensive, they were almost certainly needed to work with the 906 style rocker which didn't have a bush and ran steel against steel.

We have had a batch of shafts made to a very high standard in terms of fits and surface finish.

We have used a high spec steel which is suitable for nitriding and have applied a Nitrotec surface finish.

We hardened and tempered the material prior to machining.

After machining the parts were 'stabilised' at 610 degC to allow any movement due to the presence of residual stress to take place.

They were then ground to final size and Nitrotec Treated at 590 degC and inspected for size.

Nitrotec is a nitriding type of process developed in the Eighties and have many benefits that seem to be the right choice.

Surface hardness is 800-900HV

http://www.mamesta.nl/files/Nitrotec_E%20hst.pdf

[gled49]

I believe the original black surface treatment was a Parkerizing for oil retention against the non bushed rockers. Please chamfer groves so they won't tear up shaft bores. Gled

[chris_seven]

Parkerising is basically a phosphating treatment (mainly Manganese based).

Traditionally it uses and Acid Bath (Good for Hydrogen Embrittlement) at 180degC and does produce a porous surface to hold oil to prevent corrosion.

It is typically used for blacking guns.

Nitrotec is entirely different but also produces a very Oleophilic surface but with an underlying hardness and wear resistance that is vastly superior to phosphating.

The diffusion layer produced also assists with wear and fatigue resistance - possibly more than is required but the process is very cost effective in terms of wear resistance to cost.

With regards to chamfering the grooves, I am not totally confident that this is a good idea and will need to think about the effect on shaft retention.

As we will be producing rockers part of our thinking is to make slightly oversize shafts (and rockers) so we can hone cam carriers with damaged bores and try to salvage them btut this may not end up being very cost effective.

[304065]

Chris, great idea about the oversize rockers. Could you make one end bigger than the other so the rockers can only be installed one way? That would make installation foolproof for in-car R&R and might help with the walking.

Turbokraft makes these, perhaps you have seen them.