The rocker shaft dilemma

[Henry Schmidt]

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.

[proffighter]

Originally Posted by Henry Schmidt

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.

Hmm... I used Febi rocker shafts and RSR seals (bought both from partworks) without any issue. Tight to mount, but with Dow 55 o-ring grease it went fine.

[kmcteer]

Very interesting information Henry!

In the Cam Tower Reconditioning thread you recommend:

Originally Posted by Henry Schmidt

The simplest way to tell if your rocker shafts have adequate expansion is to use two tools (8mm allen and a 5mm allen socket and an inch lb torque wrench) to properly torque the shaft then remove the 8mm wrench and see if the shaft will turn by applying minimal additional torque. If the shaft has expanded sufficiently, it won't rotate. If it turns, you can add additional torque.
At some point, it should stop turning. If it doesn't, your cam towers are damaged and additional solutions will be required.

I suppose what you are showing here is a great additional solution that could be handled in someone garage with a file and calipers on the nuts and sleeves.

-Kelly

[PeteKz]

Henry, thank you for doing and sharing that research.

[Henry Schmidt]

Originally Posted by proffighter

Hmm... I used Febi rocker shafts and RSR seals (bought both from partworks) without any issue. Tight to mount, but with Dow 55 o-ring grease it went fine.

Simple truth is that for an o-ring to function properly, it has to rest in a given space that allows it to settle on a bottom and compress. That compression requires space.
If an o-ring is overly confined, it won't compress and in the case of a 911 rocker shaft can easily be trimmed away as the shaft is installed.
I'm sure yours worked perfectly but too tight can be an issue.
In this application the groove to o-ring clearance is .008" to .010".

[Henry Schmidt]

Originally Posted by kmcteer

Very interesting information Henry!

In the Cam Tower Reconditioning thread you recommend:


I suppose what you are showing here is a great additional solution that could be handled in someone garage with a file and calipers on the nuts and sleeves.

-Kelly

These little parts are case hardened so a file might be a challenge. I machined these in a lathe and was surprised to find how hard they are.
I have a ton of these laying around so I might just machine a bunch for exchange.

[Sniper]

Thanks for sharing your findings,really interesting approach to solving the shaft retention issue. That slight mod to the nut and sleeve to increase expansion is clever, especially given how minimal the changes are.