906 rocker arms...Value??

Competition Engineering (Lake Isabella, Calif) has finished the rebuilding of my early 1966 2.0. engine. During the rebuild, he came across the 906 rocker arms that were installed at the factory(?). The owner of Comp. Eng., Walt, suggested that back in the day they sort of grabbed any thing existing at the time to assemble the engine. Walt cleaned and polished the rockers, set them aside and installed a more suitable valve train.

Do you have any insights to my question? Thanks ...Skeeters

Attachment 437395Attachment 437396Attachment 437397Attachment 437398

How about a photo?

Hard to believe they were so short of parts that they grabbed rockers that required lash caps to set the clearance. Something the average dealer ship or shop back then wasn't likely to have. Be glad to take those nasty useless things off your hands,,,,so you don't clutter up your trash can :D

Not to mention the shorter valves :)

Good point !!

Ditto on short valves, about 2mm shorter valve stems.

How about those photos?

Are the rocker arms you're talking about by any chance forged steel with bronze bushings?

The earliest 911 engines used these. I don't know when rocker arms changed to castings without bushings but it's quite likely they were used early in the 1966 model year. Do you have an originally Solex-carbureted 901/01 engine?

The only source I can find right now is the caption on a photo in Bruce Anderson's Porsche 911 Performance Handbook. It's page 77 in the second edition.

According to Bruce's caption, the 906 (and most racing 911s) used a forged rocker arm without a bushing and adjusted valve clearance with a lash cap.

906 Rockers never had bushes and the factory original had oil grooves machined into the lower half of the bore. They were used with a 'Motorsport' Rocker shaft which had a surface treatment to prevent galling and the heel and nose were hard chrome plated.

This design of rocker was used right through at least until the 935 although the number of different thickness lash caps increased in the last few years.

The Forged Steel Adjustable Rockers lasted until the 1967 MY when they were replaced by investment cast rocker without bushes. This lasted until 1969 when the cast rocker finally gained a Glyco steel backed bush and Rocker Shafts stopped suffering from serious adhesive wear.

The change to Investment cast steel rockers took place all over Europe at around this time and was simply driven by cost. I believe Porsche also took advantage of the brittle nature of these casting to promote the idea that they made this change to save valve trains when engines lost their timing.

I also believe that the reality is that the original Mercedes inspired tensioner was poor which was the cause of cam timing problems and the cheaper rocker was just a stroke of luck.

Trying to control the impact strength of a cast steel is notoriously difficult and in 1967 virtually impossible and if you measure the force needed to break a cast rocker it is still significant.

The 906 Rocker was being manufactured in the UK for a number of years but this supply has now dried up.

They are available in Germany from Capricorn Motorsport at 600 Euros per rocker + Lash Caps. If the hard chrome is in good order the value of these rockers is quite high.

We have just produced the first batch of forgings to also reproduce this rocker and we are also machining the lash caps to the original spec.

The 906 Style Rocker has been specifically banned for Period F Appendix K Race Cars and due to this fact we have reproduced the original 1965/1966 Forged Rockers and have been supplying them for about 6 years now. and they are widely used in a number of race engines.

With have increased the length of the heel so that this rocker runs comfortably on a 906 Cam.

We have also been re-manufacturing the Surface Treated 'Motorsport' style Rocker shaft for several years.

It is a Solex-carbureted 90101. Chassis #303636

Added pics to original post

Those are standard, early forged rockers- not 906.

Jon B.
Vista, CA

Quote:

---

Originally Posted by 1red66911

Added pics to original post

---

Just as Jon B. said, those are forged early 911 rocker arms with bushings and screw valve adjustment. Here's a quick iPhone snap of the picture in Bruce Anderson's book:

Attachment 437399

The 906 rocker arm on the right is quite different.

As to what they're worth. Stoddards wants $151.76 for part # 930.105.043.05 and Sierra Madre Collection wants $133.41 for part # 930.105.043.02 which might be an earlier version or just a matter of when they got the website data.

Both of those look to be cast steel with bronze bushings.

I suppose forged rocker arms with bushings would be worth more than cast but I don't think there's much demand. Were I you. I'd put them in my engine (which is exactly what I've done with mine).

I have a singleAttachment 437430

My mystery has been solved. Thanks for all the input. Skeeters

The early race rockers didn't have oil groves. By the ST/RSR there were oil groves, don't know when exactly when groves started. The race rocker shafts I've used for 20 yrs are just parkerized standard shafts. That is what we determined the coating was. G

Quote:

---

Originally Posted by 1red66911

My mystery has been solved. Thanks for all the input. Skeeters

---

I do find it impossible to believe that Walt told you those were 906 rockers. It does beg the question though: If he used later, cast rockers which cams did he install in your motor?

Quote:

---

Originally Posted by gled49

The early race rockers didn't have oil groves. By the ST/RSR there were oil groves, don't know when exactly when groves started. The race rocker shafts I've used for 20 yrs are just parkerized standard shafts. That is what we determined the coating was. G

---

If you 'Parkerise' a standard rocker, and I would agree that this is probably the surface treatment used, it is quite possible that the shaft won't fit into the cam carrier.

There is a typical growth of around 5-9 microns on each surface which is around 10-18 microns on diameter. I thunk it would be necessary to 'process grind' the shafts before Parkerising.

This process can also result in high strength steels suffering from Hydrogen Embrittlement and the parts should ideally be baked shortly after Parkerising.

We use diffusion based treatment which is developed in a PVD Chamber, it produces an oleophilic surface layer of around 1000HV. We process grind the shaft we make before tretment and growth is controlled to a much tighter tolerance than Parkerising can produce.

We did consider Parkerising but the control of coating thickness was tricky.

Chris, you're way too technical for me. We take good used shafts chamfer the groves, polish them, parkerize them, install them in 40 year old semi worn housings and run them with 40 year old lash cap rockers. I've been running and refreshing my armature motors for decades. I'm sure there's better ways to do it than ours.

We charge around $25.00 for our new shafts with a more modern coating and we are now trying to develop a shaft without grooves and with a properly designed 'O' Ring seal in the end so we can seal worn cam carriers.

We did some very basic FEA modelling and the groove doesn't really impact on the 'swell' of the shaft.

If they work it may be a reasonable fix for leaky shafts and easier than the RSR Seals.