Rocker Arm Grinding Tool Design.

[reclino]

I am going to build a rocker arm grinder. I just purchased a slightly used micrometer adjustable X Y precision stage. On this I plan to mount a diamond dressing tool for grinder wheel and an expanding arbor sized for the 18mm ID of the rocker arm bushing. Then I can hold each rocker by the same datum. I have measured the radius of the rocker arm pad as 33 mm. I will put a bearing for rotation of the rocker at this distance from the pad. I have 18mm of travel, which is just enough to true up the face of the grinding wheel with the diamond. Then I can advance the rocker towards the stone in .01mm at a time grind the face, advance the stage .01mm and grind again. I should be able to "blue print" a set of rockers by removing exactly the same amount of material from all 12. This way at least the rocker ratio will be the same between them.

[Tippy]

Watchimg. Was thinking of this exact contraption today leaving work.

I'll be a guinea pig....

[reclino]

I am concerned that the ball bearing slides are open, I will have to make a boot to protect them from grinding debris. This stage is designed for moving precision optics, so I will have to test to see if it is stable enough once i build on it. It does feel very rigid but the rocker arm will sit up about 2" above the current surface. I will be interested on testing it on some rockers that are complete junk before I try on the spare set of lightly used ones I have.
David

[Tippy]

Can you pivot on a hardened shaft instead of bearings? Shaft and bushing may hold tolerance should hold better I'd imagime.

Curiously watching.

[KTL]

Hint

https://www.youtube.com/watch?v=HxNiWy5of7k

[hcoles]

How do you know exactly where the center for the 33mm radius is? Maybe it doesn't matter much.

[chris_seven]

Originally Posted by hcoles

How do you know exactly where the center for the 33mm radius is? Maybe it doesn't matter much.

I think the arc and its centre position does matter.

We measured a '906' Rocker' with a CMM some while ago.



We used these dimensions for the manufacture of our forged rockers which measure identically in terms of cam lift/duration to the 1965/1966 rockers we wanted to reproduce.

[Tippy]

So the radius is for sure 30mm?

[chris_seven]

Originally Posted by Tippy

So the radius is for sure 30°?

I didn't drive the CMM but the guys who made the measurements seem quite capable.

A rough check on the chord length and angle seems to stack up but small changes in the centre position will affect the radius and the absolute position of the pad.

We made our machining fixture from this drawing and when we checked 'our' rockers installed with an S cam they measured virtually identically to the standard 1966 rocker.

We didn't compare them to the 906 rockers as we are still making the lash caps.

I have never tried to measure one of the later cast rockers.

[reclino]

I was able to put my rocker on a friend's optical comparator. Made some preliminarily measurements of the stock cast rocker at 50x magnification. My radius measured 30.97mm. The pad arc length was about 43 deg. I was not really happy with how I was holding the rocker so I am going to measure again. Also this is a used but good rocker. I don't believe it had been reground but can not verify that.

[reclino]

KTL,
I have seen that YouTube video, that tool is not maintaining the proper arc or position. While that is a perfectly acceptable repair, each rocker is going to be unique. I want a tool that can make all 12 the same, and close to the factory dimensions.
David

[reclino]

So the set of used rockers I bought is a mix of B castings and 🔼 triangle castings. The one I measured today is the B. Definitely cast, rough all over, maybe sand cast, but I am no expert. The 🔼 one I pulled out of the bag to compare is MUCH nicer. Beautiful smooth surface, maybe a die cast part.
The shaft that came with the 🔼 rocker has negligible wear, while the B shaft I can just feel the wear with my fingernail. Is the B an aftermarket part?

[racing97]

My figures cam up with 31.7 for radius on the later 993 type rocker.
regards

[cmonref]

So the radius is for sure 30°?

Looks like the radius is 30 mm ("R30") over an arc of 52 degrees.

[Tippy]

Originally Posted by cmonref

Looks like the radius is 30 mm ("R30") over an arc of 52 degrees.

We have 3 different radii listed now.

I trust a CMM though! That should be dead on unless the rocker moved on the bed.

[chris_seven]

Originally Posted by reclino

So the set of used rockers I bought is a mix of B castings and 🔼 triangle castings. The one I measured today is the B. Definitely cast, rough all over, maybe sand cast, but I am no expert. The 🔼 one I pulled out of the bag to compare is MUCH nicer. Beautiful smooth surface, maybe a die cast part.
The shaft that came with the 🔼 rocker has negligible wear, while the B shaft I can just feel the wear with my fingernail. Is the B an aftermarket part?

Rockers of this type are generally investment cast.

[Tippy]

Sorry guys, I meant 30mm, not 30°. Rookie mistake....

I'm used to imperial.

[reclino]

The 906 rocker I would say is made with a 30deg rad. It is a different part from the cast rocker. I would not just jump to the conclusion that all Porsche 911 rockers share the same radius.

[chris_seven]

The rocker ratio of a 906 rocker is said to be 1.5:1 whilst standard rockers are 1.46:1 but I can believe this is within a measuring error.

The real test must be to compare with other rockers in terms of cam lift.

We have made and fitted about 40 engine sets to this drawing and have checked 3 sets in terms of cam lift.

Depending who has made the investment cast rockers I can believe there is some variation.

The man aim must be to have all the rockers the same even if the lift varies a few thou form manufacturer to manufacturer.

We are running 'our' rockers in several FIA spec 2.0 litre race cars with 906 cams and this was also part of our logic in reproducing the 906 'heel'.

[reclino]

I Measured my rocker again today on the comparator, could not get my numbers to repeat. I may have to find time on a cmm and check it that way.
David