valve rocker arm tip profiling

[Art Smith]

can anyone point me to an old article or paper on the "black magic" of valve rocker arm tip profiling? there's still some of us that are forced to make do with sliding friction on the top of the valve................ and given that, I want all the mid-lift lift the geometry can be coerced into providing for maximum area under the lift curve. I've started poking with CAD but worry about leaving something on the table................

Art Smith
artesmith@earthlink.net

[wyrmrider]

are you asking about the curve of the tip Art?

[Art Smith]

wyrmrider-

Yes AND the methodology of developing/identifying the optimum curve!!

Art
artesmith@earthlink.net

[wyrmrider]

IMho after regrinding cast iron rockers when going to more lift
trying to get a "rolling" action not a sliding action
which means getting lines across the rocker tip tangent to the valve tip as lift increases

has to be a formula somewhere
interesting question
I just did it with graph paper by hand

you have to have the fulcurm height right first
mid lift it to where the middle of your rocker pad is in the middle of the valve at mid lift
then do open and closed three points you have a curve
we ended up making new stands for the early Hemi

[Art Smith]

wyrmrider-

imposing a constraint such that mid-lift is in the center of the valve is interesting; three points will get you a circle/radius every time! class rules impose the value for maximum lift and zero is a gimme !! for discussion purposes, how would you proceed if you weren't worried about friction/valve guides?? I'm thinking the answer is much more aggressive; switching rocker shaft assemblies every time to the track seems like a doable do...................

Art
artesmith@earthlink.net

[The Radius Kid]

I would try looking at the curve they use to generate the profile of an involute gear tooth.That might give some ideas.

[Art Smith]

Kid-

involute gear profile is an outstanding idea to reduce friction; I'm fixated on finding more intermediate lift (area under the lift curve). damn the torpedo's and shallow water; full speed ahead.......................... if there's a wear problem, I'll exchange rocker shaft assemblies after every weekend at the track.

Art Smith
artesmith@earthlink.net

[Vincenzo]

This problem was addressed by Prof. G.P.Blair when he created his 4StHead software package. The solution is not a straightforward geometrical extension of an ever increasing radius, but is somewhat complicated due to the need to constantly review the next radius extension relative to the last.
The attached zip file contains a series of graphical illustrations of the method used

info centredfollower7.zip

[racear2865]

The first order of action is finding the moment of rotation at the ball pivot on the stud. Take a black tip pin and raw a line vertically from the center of the rocker arm downward. Mount a small laser beam so that it points at the top of the line. Rotate engine over. If the line moves where the laser is pointed, you are not on the center of rotation. Continue to move laser down until line does not move. That will become your center of location. Now you can began to check for dimensions in relation to scurb foot on valve tip.
reed

[ijames]

Just thinking out loud here, but it seems to me that the only way you can affect the lift is by changing where the rocker contacts the valve tip. The further the contact is from the rocker fulcrum the larger the rocker ratio and thus the greater the lift, so you always want to be just short of falling off the edge of the valve tip. You have two degrees of freedom to control this, the shape of the rocker tip and the height of the rocker (length of the pushrod) which controls the arc the rocker tip sweeps through. Of course this will maximize side loading on the valve, which has to do bad things to guide and maybe seat life. Don't know how much it would hurt the rocker life, though . Put a valve in a head with a very light checking spring, bolt on a rocker, and start with the conventional setup of tip centered on valve at mid lift, then play with raising and lowering the rocker and see what that gets you, then think about the rocker tip shape.

[wyrmrider]

you can move the pushrod side easier
but
here we are not trying to get more lift from a given lift cam- assuming they are measuring lift at the valve
moving the fulcrum up will get the valve opening quicker but causes problems near full lift
best to getting max area with mid lift then working on your valve job
remember you get maximum leverage which equals maximum lift of valve vs lift of cam at Tangent- everyplace else is less
30 degree seats or perhaps a cutter like DV is using in his BBC revisited thread would help in this low lift situation

[Art Smith]

Thanks guys; that should keep me busy and out of trouble for a while!!

Art Smith
artesmith@earthlink.net

[wyrmrider]

Art
I forget to mention that the rocker arm effectively gets longer fulcrum to stem at mid lift and effectively shorter fulcrum to stem at closed and max lift
so if you keep the same center point as in my 3 point quickie your contact point may come off the valve
so you have to move the center point as the rocker rotates in its arc
so do three points, then 5
trying to keep the contact point in the center of the valve? as in the links, I've never even tried to get that close
one reason why roller tips work

[racear2865]

Be surprised the actual lift as It scoots thru its arc. This is not a roller rolling thru a arc. It scoots the the arc and the shoe is stamped not ground.
reed

[wyrmrider]

Cast iron chryslers are ground
not much you can do with the stamped ones
their curve is only good for so much lift