Originally Posted by Nuckollsinc
Yes thats a chassis dyno 460 bbc 4500 stall th400 4.56's.
They are 3/8" pushrods
One question when checking pushrod length do you need to be at zero lash or set the rocker arm with a feeler guage? I have a solid cam and solid lifters. I did the sharpie test and both intake and exhaust are on the very back of the stem. BUT that was with setting .028 and .030 lash turning the motor 2 times by hand.
This seems to be one of those OMG moments. There is no doubt that with over .7 inch lift at the valve, that it's going to take something other than stock length push rods to satisfy the geometry between the rocker's contact point on the stem and the edge of the stem. With this much lift and 3 coils of springs the wipe area on the valve stem needs to be kept as centered on the stem as possible. But that ain't easy to do. Any off center thrust by the rocker on the valve stem will want to bind the valve in its guide and will if nothing else quickly show up as heavy wear that adds to the clearance space between the stem and guide.
The rocker tip swings in an arc, it does not push straight down on the stem, but rather as the rocker arcs it should start from the intake side of the stem and progress toward the exhaust side. The push rod length is used to establish this pattern. When you leave the zone of typical factory lifts which are mostly around .3 to .4 inch. The cam lobe height, the rocker ratio, different length valves or using lash caps, or changes in dimension of the block and or heads and interfacing gaskets all have an effect, not to mention cams that are in raised positions as is done on many race blocks.
There are two schools of thought on how the rocker sweep across the stem should be averaged out:
1) The first school would have the contact point of the rocker be in the middle of the stem diameter at mid lift. This is fine for a situation where the valve springs are not 3 rows deep and the RPMs reaching above 7000.
2) The second way of looking at this is that high spring pressures will push the valve hard over when the maximum opening point also has the rocker at the outer edge of the stem diameter. In this situation, not unlike yours, it may be better to move the rocker closer to the middle of the stem diameter at max lift to minimize the off center force when those forces are at their greatest. This will most likely drive to a compromise in that the rocker will fall off the intake side when the max lift point is selected in the middle of the stem. So this becomes one of those compromises where you do the best you can. It may be necessary to use lash caps to get the working diameter up to something more useful as well a provide a surface for the lash adjustment to beat upon beside the valve stem tip which will get hammered out in time. Lash caps may require a longer stem valve or retainers with reliefs to accommodate them such that they do not sit on the retainer.
Going a little further on your lift and bent push rods, you have to carefully check to be sure the push rods are not bound by hitting the ends of their guides, same goes for center to center distance of the guide slots, these need to line up with the rocker stud. You also need to be sure the retainer is not binding into the stem seal or the top of the guide. Plus each springs' coils need to be measured at full lift to ensure there is no coil to coil binding on any of them.
To do the push rod length checking you will have to remove the super duper 3 rows of springs to replace them with a much lighter checking spring. To do the actual checking you will need to get some adjustable push rods and go through the drill. Your regular racing springs will simply crush checking rods, don't even try it. For racing you may find it necessary to step up to .083 wall seamless, 4130, 7/16s, Manton rods or something equally insane. Do your checking with the range of lash adjustment you'd normally use on the engine as long as one end of that range or the other doesn't take the contact off the valve stem, the average position is probably good enough. Most builders would probably say not to get closer to the front or back edge of the stem than 1/3 its diameter. This can be grounds for a lash cap, but I wouldn't get the contact point off the stem diameter and solely onto the lash cap.
Check out this Comp site and Car Craft article for some how to hints: http://www.compcams.com/Products/CC-'Pushrods'-0.aspx or http://www.carcraft.com/techarticles...th/index1.html