SOHC Valvetrain Testing - Adjustable vs. Roller Rocker

Hi guys -

I've been learning a lot about pivot foot adjusters and how they behave at high rpm. If you remember, I reported trouble with the pivot foot adjuster burning up above 8000 rpm:

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The trouble is primarily due to the low rocker ratio (about 1.3 to 1)and the SOHC geometry causing a lot of scrubbing between the adjuster foot and the valve stem tip. At high speed and higher spring pressures, the heat buildup is unbelievable! Within 30 seconds of exceeding 8,000 rpm, oil smoke would start pouring out of the interface. Permanent damage to the adjuster would soon follow. I've now learned that this heating is the direct cause of the valve stem tip failures I experienced in earlier testing.

Barry R. recently got me a prototype T&D roller tip SOHC rocker. I've made up some lash caps and have tried this rocker out on the machine with a lot of success. Here's what the roller rocker looks like installed:

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I have run this rocker several times now with the 943 Spring and the 8440 cam. Where before there was soon evidence of heat above 8,000 rpm, now there is none. Twice I broke a valve stem tip off within 60 seconds of exceeding 8,000 rpm with the 943 spring and pivot foot adjuster. With the roller rocker I have held 8,500 rpm and beyond for ten minutes with no ill effects.

Here's a video of a stock pivot foot rocker running at 8,000 rpm vs. the roller rocker running about the same speed. Both cases are with the 8440 cam and 943 spring.



Notice how the stem tip is wiggling more with the pivot foot adjuster. There must be significant side loads on the valve stem in this case. With the roller rocker, everything looks much more calm and controlled. If you turn up your volume, the sound is even cleaner with the roller tip rocker.

I should say that after filming with the stock rocker at 8,000 rpm, I tore down the head and removed that valve pronto! It's marked as junk and the tip shows signs of distress. The valve I've run with the roller is still in there, having accumulated a good half hour of testing up to 9,000 rpm with no trouble. It's the same type from the same batch as the others.

I'm now confident that the valve failures I've experienced in the past can be attributed to heating from the pivot foot adjuster. Running a roller tip rocker seems to cure this problem. I think it would also be helpful to run cooling oil jets to the interface with an adjustable pivot foot setup, but it would take more testing to determine the effectiveness of that approach.

- Bill