this is an exert taken from said article of what I was getting at


Pushrod Length- Incorrect pushrod length can be detrimental to valve guide wear. Most sources say that centering the rocker contact patch on the valve stem centerline at mid valve lift is the correct method for determining the optimum pushrod length. This method is wrong and can actually cause more harm than good. The method only applies when the valvetrain geometry is correct. This means that the rocker arm lengths and stud placement and valve tip heights are all perfect. This is rarely the case. To illustrate this, think of the valve angle and the rocker stud angle. They are usually not the same. If a longer or shorter valve is installed, then the relationship of the valve tip to the rocker stud centerline has changed. Heads that have had multiple valve jobs can also see this relationship change. Note, the rocker length (pivot to tip) remains unchanged, so the rocker contact patch will have to move off the valve centerline some particular distance for optimum geometry to be maintained. The optimum length, for component longevity, is the length that will give the least rocker arm contact area on the valve stem. In other words the narrowest wear pattern. This assures that the relationship is optimized and the rocker is positioned at the correct angle. This means that the optimum rocker tip contact point does not necessarily coincide with the valve stem centerline, and probably will not. What is the acceptable limit for being offset from the valve stem centerline? That will depend on the set-up. A safe margin to strive for is about +/-.080" of the centerline of an 11/32 diameter valve stem. This means that no part of the wear pattern should be outside of this .160" wide envelope. As the pushrod length is changed, the pattern will change noticeably. As the geometry becomes closer to optimum, the pattern will get narrowest. If the narrowest pattern is too far from the valvestem centerline, then the valve to rocker relationship has to be changed. In this case, valve stem length will need to change."

 

thanks for the link. I'll have to check to see if I'm within the posted specs when I get home. I remember checking tip travel and it was within trickflows suggetsed .08 but I didn't check how far from center point I was. I know that using a 6.75 pushrod put me very close to the edge of the valve though.

 

Sometimes due to rocker and head specifications, as well as minimum tolerance differences, it can be impossible to get everything perfectly centered. Your goal shouldn't be "get the rocker dead center on the valve". What you should be doing however, is trying to get the thinnest possible witness line. Which is why an adjustable PR length checker is so important.

By starting with the TFS recommended 6.7" with your length checker, then extending the checker by .025 at a time, you will begin to see the thickness of the witness line begin to change. If the line gets thinner, as you go longer... continue to adjust it, while checking, until the line begins to thicken again. Once the line gets thicker, you know you have just passes your optimum PR length. adjust back to the last length you used, measure it and order your PR's.

Keep in mind that your intake and exhaust length may not be the same... so remember to check both.

 

ok cool I'll check it that way when I get home. So just curious. Is it better for me to be far from center but a smaller line or close to center but a bigger line? Because from checking last time I realized I ant get both. Should I just go for the smallest wear mark or try to get it somewhere in the middle? I'll psot some pics of different lengths that I try.

 

read the exert I posted, = smallest witness mark is best and still within the +/- .080 of the stem centerline

 

Thanks a ton guys got everything looking good! actually ended up being 6.55 which is weird because trickflow says 6.75. But its not going to magically change once I put the valve covers on. I checked and double checked and thats what the engine wanted. haha