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

wheel at the valve stem to see if it rotates one direction or rocks back and forth ??? .... just curious , it looks way better than the adjustable pivot

I think I'm going to need to do that. I've also noticed some inconsistent motion on the cam follower roller. It would be nice to see how much that skids on the cam lobe.

- Bill

Like I said in the earlier posts, millions of Jap motorcycles cant be wrong

I say double roller with lash caps is the way to go. Much more of a PIA for initial setup, but once finished, unless mismatched materials, it'd rarely need to be touched.

Of course you lose tuning capability of lash changes, but seems like the the longevity more than outweighs it.

I may have missed it, but whats the weight difference of the foot versus the double roller rocker?


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- 70 Fastback Mustang, 489 cid FE, TKO-600 5 speed, 3.70 9 inch
- 71 F100 shortbed 4x4, 397 cid FE, headers, Street Dominator, 280H, 5 lug Dana 60, 4 speed

The roller is actually a few grams lighter than the pivot foot. I was surprised when I measured that!

Yeah I think it would be a good idea to watch the rotation of the roller tip as well. I'll look at dabbing a spot on the roller so we can see it.

- Bill

one used a selection of lash caps to obtain proper clearance. No loss of tuning!
KS

However, convenient or not, sounds like the way to go in this application.

I have owned some ridiculously fast Japanese motorcycles in the past, and they all use some sort of lash cap/shim.


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- 70 Fastback Mustang, 489 cid FE, TKO-600 5 speed, 3.70 9 inch
- 71 F100 shortbed 4x4, 397 cid FE, headers, Street Dominator, 280H, 5 lug Dana 60, 4 speed

lots of rpm there!

The 943 spring is looking quite good at these speeds with the roller though.

I'm doing further testing with a lighter valve that should shed more light on this. I am looking forward to running beehive springs in the near future!

- Bill

nothing like a little well thought out R&D to to make life less painfull not to mention less expensive. Mike

is there oil escaping out between the rocker shaft and the cap? Nice work there Bill.

Richard.

This rotation is pretty mellow compared to other tests. There is more rotation with the pivot foot probably because the valve stem is twanging back and forth. That would cause uneven loading of the spring.

There's no seal, since the end of the rocker stand is split. I've noticed that on the aluminum head too.