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I have a 66 L79 from which I just removed an aftermarket camshaft and installed the correct 350 HP cam. While adjusting the rockers I noticed that a few of them are not sitting on the center of the valve spring. They are visual rotated around the rocker stud. Is this normal? If not what could be the cause?
Since there are no guide plates without screw in studs, the geometry is controlled by the pushrod placement through the hole in the heads. This could cause the rocker to be slightly off center if there is any bending of the pushrod, but it also will probably self center on startup anyway.....you may have rotated the rockers sligtly clockwise when tightening the ball nuts. I suspect it is fine....Craig
I did final adjustment with the engine hot and running. After stuffing down the engien several were off center. I don't know if they are off center when the engine was running.
You will rarely find all of the rocker arm palates perfectly aligned with the valve stem tip. There is no way I know of to correct lateral (i.e. side-to-side) misalignment.
Perceived "fore-and-aft" misalignment may be a function of several things. For one, is the position of the particular valve with respect to camshaft lift. The "alignment" of the rocker on the valve tip changes throughout the lift cycle.
Another factor affecting "fore-and-aft misalignment" is pushrod length. The standard small block pushrods available from GM or aftermarket suppliers have a length designed around "as designed" engine configuration. Many factors affect that, though. These include surfacing of cylinder heads, head gasket thickness, length of valve stems, and more. Generally, a PRODUCTION length pushrod will work "ok" within a certain range of deviation of the above-referenced factors. However, it will be ideal only at the as-designed configuration.
It is possible to determine the precise pushrod length required for a particular engine by using various tools and procedures available for this purpose. Then, custom length pushrods can be ordered from sources like Crane or Comp Cams. Some improvement in engine performance may be gained, too. However, few folks or street engine builders go to this effort.
By the way, there is one way to ensure perfect lateral (i.e. side-to-side) alignment of the rockers on the valve tips IF you're willing to change rocker arms. In this regard, you can use the self-guided rockers that have been standard on Chevrolet small blocks since the mid-80's, or so. In fact, GM long ago discontinued the non-guided style rockers from SERVICE and replaced them with the guided type. These are avaiable under GM #10089648.
Self-guided rockers are a worthwhile improvement. No one will know the difference once installed on the engine, either.
you MUST enlarge the "double D" shaped holes in the older heads to 7/16" dia because if you do not you are trying to align 3 points at the same time,the pushrod hole in the head,the rocker stud and the valve stem tip. also some valves may not have a tall enought tip above the keys to allow the "SAR" arms to fit down over without contacting the valve keys. they are also not reccomended for solid lifter cams,depends on the lash setting
Please take a look at the attached photo. The rear rocker is rotated to the point you can see part of the valve stem. This is with the rockers adjusted properly (zero lash plus 1/2 turn, hot method).
Looks like the pushrod guide hole in the head is worn badly and allowing the assy to rotate to one side. Not uncommon. The only way I can think of to properly repair this is to install a 1969 and later pushrod guide plate. It won't last long at all the way it is.
I was just looking at your pic again and happened to notice that it looks like there are more than just one worn pushrod guide in the head. Hard to see in the pic but I would certainly take a close look at all of these guide holes. The clearance between the pushrod and the guide should be somewhere around .020 or less (just a guess) but it looks like you have several that are a LOT wider than that.
Maybe someone can think of a fix for this but the only thing I can think of involves removing the head(s) and installing the 69 design screw in stud with pushrod guide plate. Unfortunately, this requires machining the stud boss and this must be done at a machine shop.
Yes, screw in studs and machining of the stud boss. (see post below) Also, if these rocker arms have run with this condition for a while, you may have rocker arm, valve tip and valve guide damage as well. Inspect the tips of the valves and the pallet end of the rocker arm for damage and measure the valve to guide clearance. Good luck with your project.
Based on posts in this thread in response to the photo, I need to do something. Do I need to install screw in studs with the self-guided rockers? From the name I would think not. What are my options? From reading this I think they are:
1.) the self guided rockers with enlarge holes
2.) the 69 style guides and screw in studs
Would you provide P/Ns if these options are correct?
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