I may be wrong but I believe you start with the lifter on the base circle of the cam (no lift) then you want to slide in your pushrod tool as well as a rocker on top of that. Then you want to find the pushrod length that has the tip of the rocker a little farther than half way across the tip of the valve. That way, when the rocker pushes the valve down, it will center on top of the valve. Make sence? If not just ask another Q? hopefully someone with a little more experience will come by and validify my statement.
Tyler
BTW where abouts is Richardson? Im in Big spring, I doubt you know where that is as it's a small town West TX
With the valves closed the roller tip should be before the valve tip center, when the rocker pushes the valve the roller will go to and pass the valve tip center and then back as the valve closes. You want a pushrod that places the roller tip so it travels the same distance before and after the center. You can use a felt tip marker to get a pattern on the valve tip or just get real close and eyeball it. Better to have the pattern closer to the rocker arm than away if you cant find the exact pushrod lenght, shorter pushrod. I use manley pro swedge and trickflow one peice pushrods, manton makes some nice stuff also.
honestly i don't. i have read this forum around 10 times and i still don;t get it. i am more of a visual or hands on learner. ill just keep reading though, unless someone feels they can really dumb it down for me
:SNSign:
Put some grease on the valve tip then put the rocker and push rod on and ajust it. Then turn the motor over one time so the valve opens and closes. Then remove the rocker and it should of left a pattern on the valve tip in the grease. It will just be a clean mark in the grease. If this mark is in the middle of the valve tip then your fine. If it is close to one edge and not the other then you need different push rods. I'm not sure if shorter moves in in or out but I'm sure someone who know will chime in. You really only need to check the exaust and intake on one cylinder.
Hope this helps.
Go here: http://www.mid-lift.com/intro-mid-lift.htm
After reading each page, click on the illustration to go to the next. You will get the complete picture on how to get proper pushrod length as well as how the valve train works.
Basically, the rocker tip moves across the valve stem (inline with long axis of the rocker). You want to choose a pushrod length that MINIMIZES that travel. The less travel, the more the rocker is pushing vertically on the valve, which produces all of the lift on the cam lobe. Any pushrod length other than optimal will reduce lift. Excessive travel on the valve tip is to be avoided.
Much of the Miller Engineering site is dedicated to solid lifter valve trains. A simplified method for finding pushrod length would be:
QUOTE from Jim Miller in email I received:
The simplest way to check geometry is close valve, base circle cam position; and using an adjustable pushrod set the trunnion (or shaft) centerline half of the net valve lift BENEATH the roller pin centerline, as measured evenly across the top of the valve spring retainer. NET means after lash is removed - or
allowing .020" compression for hydraulic tappets.
...when the rocker's pivot point (trunnion) is set correctly, it will be below the roller pin half of the net valve lift, when checked in the closed valve position.
This is the same illustration on the "INSTALLED GEOMETRY" page, which you can find in the MASTER INDEX.
UNQUOTE
If you study the website above, you will understand what this means. Reading it cold ... you prolly won't get it. Reading the MEI site is very illuminating and I recommend it to everyone who wants a better understanding of valve train geometry.
Very interesting read at the MEI site. If I understand the theory correctly I should use a different length for intake/exhaust on my split duration/lift cam. However the difference between 1/2 the net intake lift and 1/2 the net exhaust lift is only .0192". I will probably just split the difference. I am curious how closely the Car Craft tech article method will match the Mid-Lift technique. I may try both just to see.
mustbereel: Mine came out to 6.320 and 6.340 - I also had valves with slightly different tip lengths (spring package from Ed Curtis - not AFR springs) to change things up. I used Smith Bros. (Bend Oregon) pushrods. When I called them, they said that those would be custom lengths. They recommended 6.300" and 6.350" and thought that I wouldn't have a noticeable difference in performance witha hydraulic cam. The exact optimum length with a hydraulic cam isn't easy to determine anyway for a number of reasons (i.e., inside 0.050" or so), according the MEI. They just recommend adding the 0.020" to the measured length to account for lifter preload.
If any one should buy MEI lifters, you will find their tech help to be very good. I exchanged several emails with Jim Miller and he was always helpful - and VERY knowledgeable, of course. I bought mine on ebay for a good price. My tuner remarked (when I told him what rockers I used) that those were the best there were. Their stand-based rockers are awesome, but I just didn't need them with a 6500 RPM/hyd. cam'd motor.
BTW, the Car Craft article is shooting for minimum travel across the valve stem, if I remember correctly. If that is achieved, it should produce the same results as mid-lift.