Valvetrain geometry

[deckert]

Engine build is 390 to a 418.
Roller cam/lifters with Harland Sharp /s4006bke rockers
Heads are Edelbrock/60065
With this setup above, I need to shim my rockers up .225" to get my rockers perpendicular to the valve which puts the roller tip in the valve center at mid lift. My valve train, with shims, is setting like the middle image in the attachment.

Here's a response I received from one company: The problem people often run into with this application is they are trying to set up the geometry different then the way the original engine geometry was designed.  The Ford FE engine was originally designed to have the tip of the rocker start on the inboard of the valve stem and sweep to the outboard side at full open lift.  I have looked at several different heads and factory rocker assemblies and they all do the same thing.  Start on the inside of the valve and sweep to the outside. I have a set of the Edelbrock heads here and when I put the rocker assembly on it and the factory head they have the same geometry.  In the past few years what I have learned is people try to setup this rocker assembly with a mid lift or SB Chevy type geometry.

Should the rocker roller tips travel from side to side on the valve tip or should the rocker be perpendicular and have minimal travel on the valve tip?

I have no idea if the 'reply' is correct but it left me wondering whether I should just go with the flow or set the geometry to minimize travel on the valve tip? My personal opinion is to minimize but I'm curious what/how others view this or what was your approach/solution?

Dan

[jayb]

My opinion only, but on less than a really high RPM engine with a lot of valve spring, it may not matter that much.  Having said that, if I was going to make an adjustment to the stand height in order to optimize rocker geometry I would do it as your attachment recommends, so that the roller sweeps back and forth across the valve as it opens.  I can't say that I've ever looked at a factory rocker setup to know how the factory geometry worked...

[blykins]

IMO, if you're gonna take the time to go through the motion, I would focus on minimizing the sweep across the valve stem and make that the highest priority.  The second priority would be trying to center it as much as possible on the stem.  With a little bit of work, shimming, or milling, you should be able to get about a .050-.060" pattern on the tip pretty easily. 

Minimizing the sweep means that you're are netting the most lift that you can. 

What I see passed around the most is that the pattern *has* to be centered on the tip.  Rarely does it happen that way and that's certainly not a priority. 

[mike7570]

Here is the rest of the article:

http://www.eatonbalancing.com/blog/2007/12/

[deckert]

The build will be used as a daily driver in a '71 F-250/CS with a T-18/4spd & 4:10's. I just wanted something with a tad more umph than the 'ol 390 had and sounded/ran better .

But the shim height for the rockers really made me wonder what other people did with ED heads & HS rockers? I find it hard to believe I'm the only person to hit this snag/issue? FWIW, I've spent a whole lot of time trying to find a solid answer with no luck so far.

Hindsight being 20/20, I just should have ordered the 445 from Barry and been done with the BS but I didn't want that much HP for my truck. I'll have what I want after all the BS but it's been a PITA.

Dan

[WConley]

I would agree with Jay and Brent.  I think the stock FE geometry was set up with the rocker low at zero lift, sweeping out to max lift.  This provides a slight packaging benefit by allowing a lower valve cover and /or more room for internal PCV baffles. 

IMHO with a roller tip you're splitting hairs trying to get the perfect geometry that Ted Eaton suggests.  There's not going to be a whole lot of side loading going on, as you'd see with a non-roller stock setup.  The lift that you pick up with all of that shimming work would be minimal.

I wouldn't sweat it.  Pay more attention to setting up your springs with proper tension and getting to within 0.050" of coil bind at full lift.  THAT will pay off in spades with better valvetrain control for long life in your daily driver.

[gordonr390]

So the take away here is that a 3/8" valve stem doesn't wear or create harmonics near as much as would a 5/16" or 7mm valve stem would?

[Ford428CJ]

Here is mine. Centered on the valve stem.

[gordonr390]

Here is mine. Centered on the valve stem.

Nice work "Ford428CJ". I build race V-Twins that use shaft mounted rockers. By using special fixtures to figure stem length and rocker height this work takes time to figure out for sure, but is well worth not having possible issues with spring failure and guide/valve wear. A properly setup rocker geo also doesn't require roller rockers. In Harley world a stock hardened rocker arm has less deflection than a roller that is not hardened.

[Ford428CJ]

Thanks Gordon! I had to shim my rockers up to get the  correct geometry. Little time-consuming but well worth it.