At first glance everything looks good; a 6B23 (23 Feb 1966) date casting, Comp Cams Magnum Roller Rocker Arms, Erson Cams Guide Plates, all nice and clean. Then I see the poor wear patterns on the roller tips, and how the leftmost rocker is slipping off the center of the valve stem.
I had a similar problem with my stock 289 heads back in high school. The factory mills a rectangular slot in the head to guide the pushrod and thus keep the rocker arm aligned with the valve stem. The problem with that is if things don't line up perfectly then there's no adjustment. If the rocker isn't centered over the valve stem then it wants to slip off the side, putting unwanted side forces on the pushrod and rocker fulcrum. The solution it to open up the factory pushrod guide which is milled in the head and install aftermarket guide plates that mount under the rocker arm studs. This, unfortunately, requires removing the head so the factory press-in rocker arm mounting studs can be pulled out. Then the heads are drilled and tapped for screw-in studs.
Fortunately for me this has already been done, and yet, my rockers are still crooked. Normally, you would loosen the rocker arm studs, slide the guide plates around until the rockers are aligned, and then tighten the studs. But in my case I can actually push the rockers into alignment by hand since there is way too much side play. The roller tip on the rocker can shift side-to-side by around 3/16". Looking at the 4th rocker arm above, the pushrod is nearly touching the left side of the guide, while the 3rd rocker has a large gap between the pushrod and the guide plate.
I twisted a rocker arm to push the pushrod to one side of the guide plate so I could measure the clearance on the other side.
I didn't have a feeler gauge big enough so I had to stack 4 together to fill the gap. Its hard to find an exact figure on what the clearance should be but 0.012" seems like a safe minimum. In my case I have (at least) 0.078" which is 0.066" too much. I measured the width of the guide plate and it looks to be 0.391" which just happens to be 0.016" wider than a 3/8" pushrod, but way too wide for my stock size 5/16" pushrods. So I need to buy either fatter pushrods or skinnier guide plates. Guide plates it is.
I am concerned that the correct size guide plates may not entirely solved my rocker alignment issues. Yes, they are adjustable, but the slots are still a fixed distance apart so both rockers get adjusted the same amount. The intake rocker could end up perfectly aligned while the exhaust is off by a little. They do make 2-piece guide plates that let you align each rocker independently, but they need to be welded together to maintain their alignment.
I'll try the 5/16" one-piece guide plates first before I resort to the bikini (two-piece, get it?)
UPDATE: This problem has been corrected in my post You're Fired!
