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
Last edited by 1red66911; 10-11-2017 at 02:52 PM. Reason: adding pictures
1966 Porsche 911
1960 Chevrolet Corvair Monza 900
2000 911 C2
1979 Crossle F-35 F/F
1969 Lynx Mk 2 F/V
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
Early S Registry member #90
R Gruppe member #138
Fort Worth Tx.
Not to mention the shorter valves
Good point !!
Early S Registry member #90
R Gruppe member #138
Fort Worth Tx.
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.
Jim Alton
Torrance, CA
Early 911S Registry # 237
1965 Porsche 911 coupe
1958 Porsche 356A cabriolet
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
1966 Porsche 911
1960 Chevrolet Corvair Monza 900
2000 911 C2
1979 Crossle F-35 F/F
1969 Lynx Mk 2 F/V
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