RSR Rocker Shafts

[chris_seven]

I have been looking at the RSR Rocker shafts used with the 'solid' 906 Type Rockers and am trying to learn what surface coating has been applied.

The 906 Rocker doesn't have any bush fitted and runs directly on the shaft.

The 'Motorsport' shaft has a black finish and I was led to believe that the shafts were 'Nitrated'.

From this I assume that they were Tenifer Treated to eliminate any galling.

I have recently seen a comment that the shafts were 'moly' coated and this seems a much better idea.

Does anyone have the correct solution. I would also be interested to know if anyone had fitted a modern GBB type bush in the RSR rocker and then ised a standard shaft?

[cgarr]

We have used the modern permaglide bushings in stock bushed rockers. I guess if you could accurately bore the rockers to accept the bushing it should work just as well. You might see a bit higher lead content in your oil when its analyzed since the bushing contains a fair amount.

[chris_seven]

I was think about using this one:



It is lead free and can run a 5 metres/second at reasonably high loads and boring should be relatively easy.

I am still interested to look at surface treating shafts just to see how it may work.

I have seen some shafts in other engines that are gas nitrided and then polished and DLC coated but this eems a bit extreme.

[cgarr]

Is that a steel shell with on overlayment of bronze?

[chris_seven]

It is a lead free and higher speed version of DU materials.

I spent quite a reasonable amount of time providing data to the manufacturer and the bronze version seems to tick all the boxes.

The maximum radial dynamic load capability is identical to DU with a steel backing.

The bronze backing has a lower static load capability than the steel backed bush but I think the dynamic load capacity is the most important.

There is also a lead free version with a steel backing that is about 50% of the cost of the bronze version.





This one has the same static load capacity as DU and the higher speed rating of the bronze bush and is also lead free.

I guess either would be OK and the manufacturer has probably recommended the most expensive.

[cgarr]

Those look like the ticket! Back when I was researching this years ago the only problem I ran into was getting a small run. All the manufactures I contacted wanted a 10k piece order before they would even talk to me. I only use about 200 a year so I had to use what they had on the shelf.

[chris_seven]

Craig,

These are in stock at my local supplier of bushes and are available in 100 off bags.

They have a size that I think is correct for a standard rocker. 18.0 ID x 20.0 OD x 25.0 Long nominal sizes.

I have been using a smaller version to re-bush the throttle shafts of Solex 40PI carbs and then fitting a PTFE Rotary Shaft Seal and they have worked very well.

If you want a bag I can post them across without problem.

[cgarr]

Interested! PM sent

[hcoles]

sub

[chris_seven]

Replied

[tadd]

Chris:
Forgive me for asking what may be a dumb question, but how are you going to bore a solid 906 rocker? The 'OD' of the solid rocker is smaller than the cast rockers by like half. There just isn't a a lot of material to remove.

Curious cause I've in this boat and the 'new' motorsport rockers are 2.5x the stock. I've also looked at the treatments you've been kind enough to suggest in the past but the set up costs for a small batch are nasty prohibitive.

I've been told that DLC at $25 a pin is the way to go, I just hate to put the wear on the hard to find part...

t

[PFM]

Chris,

You might want to talk with these guys MICROBLUE® | The coating that changes the way lubricants work and possibly skip the bushing all together. If boring the rocker makes it too thin you loose, I like DLC for pins but think this may be more affordable and quite possibly a better fit.

[chris_seven]

Originally Posted by tadd

Forgive me for asking what may be a dumb question, but how are you going to bore a solid 906 rocker? The 'OD' of the solid rocker is smaller than the cast rockers by like half. There just isn't a a lot of material to remove.
t

Tadd, the discussion about permaglide type bushes is a bit of a sidetrack as I don't have any solid rockers to machine.

It is interesting, however, that the 'boss' on the solid rocker has identical dimensions to the early (1965/66) forged adjustable rocker and this was bushed.

I think that the solid rocker is quite strong enough to allow boring for a bush and I have a 3-D model of the forged rocker which I can plug into a FEA programme and try to see what the stresses look like.

Originally Posted by tadd

Curious cause I've in this boat and the 'new' motorsport rockers are 2.5x the stock. I've also looked at the treatments you've been kind enough to suggest in the past but the set up costs for a small batch are nasty prohibitive.

I've been told that DLC at $25 a pin is the way to go, I just hate to put the wear on the hard to find part...
t

The lowest price I have found for the solid rocker is around $500 each. If you add the 'Motorsport' Rocker shafts and lash caps you end up just the wrong side of $7500 + Sales Tax, which is frightening.

I agree with your comments about DLC treating the shaft as all wear would concentrate in the rocker but the wear rate is likley to be very low.

I would also worry about the DLC coating cracking on the ends of the shafts where the hoop stress causes slight deformation to lock them into the carrier.

I think nitriding the shafts is likely to be a better solution and more likely to tolerate the local deformation.

If the solid rocker were bushed it would run on a standard shaft and maybe this is the best solution.

There are some rockers available that are billet machined and this would be seem to be a relatively cost effective solution but when I discussed them and sent photographs to an FIA Historic Eligibility Scrutineer and he said he would reject this type of rocker for use in Appendix K cars.

Having said that billet machined rockers are being sold for $360 each + Sales Tax.

Originally Posted by PFM

MICROBLUE® | The coating that changes the way lubricants work and possibly skip the bushing all together. If boring the rocker makes it too thin you loose, I like DLC for pins but think this may be more affordable and quite possibly a better fit.

Mmmm! Good old Snake Oil. Please excuse my cynicism but I always worry about this type of claim when not backed up with any real explanation of the mechanism that produces these amazing results.

[tadd]

Chris:
I'm sure you know what these look like, but I just thought I'd add this incase I'm calling this the wrong thing incase these are 935 or something.

Forged solid shim '906' rocker and cast rocker. Bushing looks to be 0.035". Thinnest outside on the forged rocker is 0.093", so it would be 0.050ish once opened up for a bushing.

If you say they are strong enough bored, then that is what ill do since that really is the best solution with the permaglide material cgarr uses.

t

[chris_seven]

I agree that the 'boss' on the cast rocker is different but I think the boss on the 65/66 adjustable forged rocker is quite similar in size to the 906 type rocker but does have a bush.

The lead free bushes I was going to use to replace the old bushes in the adjustable forged rockers are 18mm id x 20mm od x 25mm long. I would imagine the Permaglide bushes are a similar size.

One issue I have with most of the 906 Type rockers I have seen is that they have been 'polished' and mucked about with.

The original profile seems to be much 'sharper' and better defined.

[Flieger]

I read Hans Metzger's book Porsche and Me just recently. It was a very good book. His first major task at Porsche was to derive a formula relating valve lift to cam profile to make it easier to manufacture the cams for the F1 engine which used finger followers. The formula had something like 30 variables including the forward and backward derivative of the valve lift. The formula worked, checked with hand calculations (!) and a computer and it was subsequently used on all Porsche engines which used finger followers or rocker arms, including the 911.

So now I realize that modifying the rocker arm pad profile is not something to take lightly!

[hcoles]

Originally Posted by Flieger

I read Hans Metzger's book Porsche and Me just recently. It was a very good book. His first major task at Porsche was to derive a formula relating valve lift to cam profile to make it easier to manufacture the cams for the F1 engine which used finger followers. The formula had something like 30 variables including the forward and backward derivative of the valve lift. The formula worked, checked with hand calculations (!) and a computer and it was subsequently used on all Porsche engines which used finger followers or rocker arms, including the 911.

So now I realize that modifying the rocker arm pad profile is not something to take lightly!

This gets me thinking that having the rocker pads "buffed" and still retaining the exact lift as a function of crank position may not be trivial. There are places that do this and I've had my rockers processed at one of them in San Jose CA. I don't know how the buffing path is controlled, I'll bet it is just a displaced curve path from a known stock rocker which may not result in what we ideally want. Let's see if one or more of these machinists will explain this to us.

[chris_seven]

I think it is safe to say that if material have been removed from the rocker face then the lift and potentially the effective cam profile will have changed.

The question is whether or not enough change has been made to measurably affect performance.

I am sure it was common practice to re-plate and re-grind hard chromed rockers but this should mean that the original profile was maintained.

A cam-follower mechanism has a two degree of freedom cam joint that connects the input
and output links. The relative shape of the cam and follower define the displacement
function of the mechanism.

The geometry of the follower is usually simplified to a point, line or circle, and combines
with the displacement function to define the cam profile.

Even if the profile has been maintained in terms of the arc it is possible that the rocker ratio has been affected and it would also be worth checking to see if all the rockers had the same effective ratio.

[hcoles]

I think that the ratio for all rockers if a small amount if material is taken off and lift should not be too much of a problem for the adjustable rocker.
Does anyone here know the geometry of the pad? Is it an arc? What is the radius? Where is the center of the radius, assuming it is a simple arc.
A more basic question - is the cam profile two circular arcs connected with two lines?
Yes agreed - perfection is not needed if there is no negative effect on smoothness or performance. How close to each other do they need to be in terms of lift vs. rotation or area exposed vs. rotation whatever measure is appropriate.