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I'm not sure that shimming will make it worse,
take it to the extreme i.e. if you shimmed it an inch, the arc of the tip would be passing the valve on the inside, or is my reasoning wrong??

Joe

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that was my thought , but that was ASSuMEing the rocker shaft holdown pedestals were parallel to the valve stems , they angle toward the valves it seems, I don't have a head handy to confirm this.

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I'm not sure that shimming will make it worse,
take it to the extreme i.e. if you shimmed it an inch, the arc of the tip would be passing the valve on the inside, or is my reasoning wrong??

Joe

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If the valve-side lever length is wrong (more common than we would like) re-arranging the heights to cure it will make the geo worse.
The "scrub path" length and behavior on the stem is far more important.

The best path is the shortest, and begins at 0% lift (valve closed) with the roller tip closest to the rocker shaft, and to the stem’s near edge (not the center).

As the valve opens, the roller walks toward the stem center, is centered in its own path (which may not be the stem tip’s center) at 25% lift.

It reaches its farthest point away from the rocker shaft at 50% lift, then reverses direction.

The roller walks back, reaching its path center again at 75% lift.

Full lift is, again, at the closest point to the shaft and its original resting place.

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Yes, that is also a very good point. The factory rocker arm geometry is designed for valve lift of roughly 0.400 inches. Which is exactly what you would expect since that is what the lift was when those heads were designed in the late 50's.

To keep the geometry correct, you have to lower the rocker shaft into the head 50% of the additional lift. So if you go from 0.400 lift to 0.600 lift, the rocker shaft should be lowered 0.100.

The only reason to use shims if if you are running less lift than the original design of 0.400. Most people don't do that.

The problem is that if you lower the rocker shaft it moves away from the valve so then you need a longer rocker arm. Best fix for stock heads is to mill off the pads and use offset blocks like the factory designed for the W2. Then you can lower the shaft and move it into position. But then you need to modify the pushrod holes and all of that jazz.

I think the serious class racers used to do all of this stuff years ago. Not sure if anyone still does it anymore. They probably just send their heads to Jesel for modification if Jesel valve gear is allowed in the class rules.

I wrote up all of this information years ago in a magazine article and then covered it again in my big block book. Not sure why I'm bothering to type it in again here.

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Yes, that is also a very good point. The factory rocker arm geometry is designed for valve lift of roughly 0.400 inches. Which is exactly what you would expect since that is what the lift was when those heads were designed in the late 50's.

To keep the geometry correct, you have to lower the rocker shaft into the head 50% of the additional lift. So if you go from 0.400 lift to 0.600 lift, the rocker shaft should be lowered 0.100.

The only reason to use shims if if you are running less lift than the original design of 0.400. Most people don't do that.

The problem is that if you lower the rocker shaft it moves away from the valve so then you need a longer rocker arm. Best fix for stock heads is to mill off the pads and use offset blocks like the factory designed for the W2. Then you can lower the shaft and move it into position. But then you need to modify the pushrod holes and all of that jazz.

I think the serious class racers used to do all of this stuff years ago. Not sure if anyone still does it anymore. They probably just send their heads to Jesel for modification if Jesel valve gear is allowed in the class rules.

I wrote up all of this information years ago in a magazine article and then covered it again in my big block book. Not sure why I'm bothering to type it in again here.

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so why not just use a longer valve ?

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"Why would you say it all again? Don't get involved with lil guy questions
Let him buy your book and figure it out

You can stay " up here" "
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And we'll be "down here" helping each other because were mopar"



You got something against Andy trying to help someone out!

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And second the hold down bolt vs valve stem angle..

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Good picture , now I see why going up with the shaft will make it worse. Looks like I may have to shelve the HS rockers and go for something else on my 906's

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I've saved a few pictures from threads about rocker geometry in the past... First the rocker arm length that Andy mentioned... It would be nice it the rocker brands were mentioned ....

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