Valve train geometry

[70MC]

Its been said that you want the smallest wear pattern in the middle of the valve, for your geometry to be correct. What i'm seeing on my s.b.c. is that the smallest wear pattern is just off center toward the exhaust. With a 8.050 pushrod my wear pattern is in the center of the valve, with a 8.100 pushrod i have a wear pattern that is about .020 smaller but is about .020 off center toward the exhaust. What would be considerd correct, or best, wider and in the middle or a little narrower and slightly off center?

[speedtalk]

This situation sucks.

When you look at a SBC the rocker stud and the valve, angle towards each other. So, when the valve gets longer, the rocker should have a relocated roller - towards the stud. Unless you want to have custom rockers made, I'd put the pattern in the middle.

[maxracesoftware]

>>What would be considerd correct, or best, wider and in the middle or a little narrower and slightly off center? <<<

out of those 2 Choices , i'd go with the "least" narrower contact patch

but like Don stated => it would take a custom set of rockers to get geometry perfect sometimes !

you need the "LEAST" sweep on the pushrod side as well, its worth more HP/Torque gains on the pushrod side

and better valve guide life on the valve side

Pushrod side= HP/Torque
Valve side= Longevity/Life..less wear/tear

[joe]

Also be aware that having the rocker tip move from the inside of the valve tip to the outside is better than the other way around . It doesn't load the guide as much.

[ozrace]

Also be aware that having the rocker tip move from the inside of the valve tip to the outside is better than the other way around . It doesn't load the guide as much.

Joe
If the rocker does a normal arc from a normal starting position, it has to initially move from the inside to the outside , and then return from outside to in - hopefully reaching the fartherest point in it's travel at mid lift.
I can't see how it could ever move from the outside to the inside only unless the geometry was an absolute mile off.

[joe]

Let me define inside and outside too ensure there's no confusion . I call the side near the valve cover rail the outside and the inside is near the stud . It is typical for the rocker tip too start "out" and move "in" on a sbc you can visualize it . remember that the stud and valve stem point toward one another . When the valve moves DOWNWARD it gets farther from the stud . When the rocker axis ,on the valve side , is 90o too the stud the tip is as far out as it can travel in it's arc.
These things are both difficult to describe and visualize. I hope I haven't created more confusion !

[joe]

I was right the last post only added too the confusion ! The roller tip is always the same distnce from the axle shaft (trunnion) , but where the arc meets the valve tip is the topic here ! I gotta remember that !
It would be so much easier if you could look at these drawings I've made !
If the roller rocker tip , on the cams base circle , is closer too the inside of the stem tip; and the rocker ,over the valve spring , is at a greater angle than 90o when the rocker swings thru its arc it will move towards the center of the valve tip , thus moving *inside out*

[ozrace]

I understand what you mean Joe, but I have never seen the geometry that far out (where the rocker starts already past 90 degrees). That would certainly be very hard on the valve and guide, and would have a very wide pattern, as you are moving the rocker in one direction only.
Having the desirable narrow pattern requires that the roller tip starts above 90 degrees - move firstly out, and then back to the starting point.

[joe]

YES we're in agreement when I said "greater than 90o" I meant from the bottom of the stud . one more time.


The rocker stud and valve stem are perfectly parallel (we'll assume) the rocker arm tip is , lets say 120o when measuring angle from lower half of stud .The rocker tip is thus nearer too the inside of the valve stem . When the pushrod goes UP and the angle becomes 90o (at about half lift ) the roller tip is now FARTHER from the stud centerline and thus closer to the valve stem center . Now the roller tip moves back toward the inside of the stem (relatively) as the angle has become less than 90o . Then the pushrod goes DOWN reversing this turn of events .
(these figures are for demo only actual angles will vary)

You know this is kinda like those pics you see where you can picture either a couple kissing or a vase in between , once you've visualized the one it's hard too see the other image without changing your thought process !

[TALON4169]

Good Morning gents

Is this picture/diagram of use http://www.compcams.com/Technical/Products/Pushrods/

Mr Terrill this forum is a great site.

Jim

[speedtalk]

Mr Terrill this forum is a great site.

Thanks Jim and welcome to the forum. Please consider signing up. It does make the site easier to use.

[Guest]

Good afternoon

I am registered...just can't seem to log -in? I tried to re-register and the software told me the e-mail address was already registered. I can't find the confirmation e-mail with my password etc. Maybe I'll get a chance to figure it out tommarrow.

Jim

[talon]

Okee Dokee

I believe I got this register and log-in ok now.

Sorry

[Stocker]

What about stamped steel rockers , that have no roller ?
Mike...

[Racer7088]

I always wondered where Comp got that drawing! you'd have to shorten the push rods way up to get it to where the tip only travels across the valve to the exhaust side all the way down! This situation needs a longer pushrod to start shortening up sweep.