Cam Tower Rocker Shaft Rebore

[Rosco_NZ]

What doesn’t anybody offer oversized rocker shafts to enable the cam towers to be rebored, and cure all those oil leaks????

[914efi]

Good question. Not just about oil leaks but also good retention if the bore is damaged. Is there a speedy-sleeve style solution? Making larger shafts is a fairly simple project but it is still work, and the devil is [always] in the details...

I saw a post about a service boring for larger journal cams, that guy should have good thoughts on this.

[Rick Cabell]

Then you would need to bore the rocker and make new bushings and bore to size, gets expensive.

[914efi]

Will the rocker bushings handle being honed or reamed 0.010" larger? That is probably all that is needed to clean up the bores. The small increase would imply a larger rocker shaft, a sleeve might not work with such a thin wall.

[Rick Cabell]

No it would not.

[Henry Schmidt]

Stay tuned.
We are currently experimenting with two "new" processes that should help with 90% of the rocker shaft/cam tower issues.
I'm excited by test results so far, and if successful, should offer a relatively inexpensive option for overly expanded rocker shaft bores.
It won't compensate for gouged or seriously damaged bores but they both look promising for most rocker bore issues.

[RobFrost]

Do the rubber seals that slot in to rocker shafts not work?

Sent from my SM-S918B using Tapatalk

[Henry Schmidt]

Originally Posted by RobFrost

Do the rubber seals that slot in to rocker shafts not work?

Sent from my SM-S918B using Tapatalk

RSR rocker shaft seals help to seal an imperfect rocker bore.
That said, the issue facing a number of builders is that the bores in the cam housings have been expanded beyond the shaft's locking mechanism is capable of expanding. This leaves many engines with the issue of rocker shaft movement.
This issue shouldn't even be an issue accept for want-a-be mechanics who over torque the rocker shaft.
Stay tuned, we've identified the problem and working on two different paths to resolve the issue.
Now for the real world testing.

[Rosco_NZ]

I will def keep abreast of the Supertech solution. I’m amazed with all the aircooled luv out there it’s taken this long.

[RobFrost]

Originally Posted by Henry Schmidt

RSR rocker shaft seals help to seal an imperfect rocker bore.
That said, the issue facing a number of builders is that the bores in the cam housings have been expanded beyond the shaft's locking mechanism is capable of expanding. This leaves many engines with the issue of rocker shaft movement.
This issue shouldn't even be an issue accept for want-a-be mechanics who over torque the rocker shaft.
Stay tuned, we've identified the problem and working on two different paths to resolve the issue.
Now for the real world testing.

Thanks, that's interesting to learn. How can I tell, when tightening my rocker shafts, if they are are not gripped property and prone to movement?

[David Inc.]

Originally Posted by Henry Schmidt

RSR rocker shaft seals help to seal an imperfect rocker bore.
That said, the issue facing a number of builders is that the bores in the cam housings have been expanded beyond the shaft's locking mechanism is capable of expanding. This leaves many engines with the issue of rocker shaft movement.
This issue shouldn't even be an issue accept for want-a-be mechanics who over torque the rocker shaft.
Stay tuned, we've identified the problem and working on two different paths to resolve the issue.
Now for the real world testing.

When you say over-torque, what kind of values are you saying? I remember reading that some amount of torque over spec is recommended for older engines, but I always felt iffy on that.

[Henry Schmidt]

Originally Posted by RobFrost

Thanks, that's interesting to learn. How can I tell, when tightening my rocker shafts, if they are are not gripped property and prone to movement?

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.
Turbo Kraft has a elegant solution where they replace the rocker shaft nut and sleeve with flanged pieces that locates the shaft to prevent them from coming out.
This solution combined with RSR seals should provide good results.


https://parts.turbokraft.com/collections/911/products/rocker-shaft-lock-set

[Henry Schmidt]

Originally Posted by David Inc.

When you say over-torque, what kind of values are you saying? I remember reading that some amount of torque over spec is recommended for older engines, but I always felt iffy on that.

The correct torque for unmolested rocker to cam housing is 1.8mkp approximately 160inch/lb. or a little more than 13 ft/lb.
I've seen "expert" on the forum suggest 19, 20 and 24 ft/lb which is how we find ourselves in this dilemma. Sometimes "more" is not better.
If you find that 160 inch/lb is insufficient to guarantee retention, add some. How much is where the nuance of craftsmanship comes in.

Let's see how many experts chimes in to say they use X and never had a problem...
Evidence of the excess of damaged cam housings would suggest differently.

[RobFrost]

Thanks again, Henry.

[David Inc.]

Originally Posted by Henry Schmidt

The correct torque for unmolested rocker to cam housing is 1.8mkp approximately 160inch/lb. or a little more than 13 ft/lb.
I've seen "expert" on the forum suggest 19, 20 and 24 ft/lb which is how we find ourselves in this dilemma. Sometimes "more" is not better.
If you find that 160 inch/lb is insufficient to guarantee retention, add some. How much is where the nuance of craftsmanship comes in.

Let's see how many experts chimes in to say they use X and never had a problem...
Evidence of the excess of damaged cam housings would suggest differently.

Very good info, thank you.

[Henry Schmidt]

Use this link to see what we found.
Phase one testing complete.
Next phase to follow.

https://forums.pelicanparts.com/911-engine-rebuilding-forum/1180275-rocker-shaft-dilemma.html