Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Achieving Proper Rocker Arm Geometry
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Old 08-10-2012, 06:34 PM
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Originally Posted by Grant4060 View Post
I've tried several different roller rocker arms with the mid-lift method and there was a considerable difference. The first try was the steel Comp rockers- If I got the correct mid lift point on the valve end, I was way out on the pushrod side. If I corrected the pushrod side to the 90 degree mid lift position the valve end was way off. My conclusion was that the rocker did not have the correct angle between the pushrod end and the valve end (big block chev). I then tried a set of Jim Miller's rockers I was lucky enough to find. His rockers were correct on both ends, I was able to get 90 degrees at mid lift on both the valve end and the pushrod end! I did need to go way longer on both intake and exhaust pushrods, one more than the other. From memory I think it was around .200" longer, but every engine will vary. My point being that not all rockers are correctly manufactured, so it does pay to try another brand or style if you are not getting the results that Miller describes in his articles. Also, I had to install longer rocker arm studs to provide enough threads for the polylocks once I installed the longer pushrods. Miller explains in his article how roller rockers were incorrectly designed originally, and many have not been changed to this day. Too bad Miller rockers are not easy to come by, I understand that he only now offers a very high end "Pro" rocker on a special order basis (if at all)....
Pester him he reads this site from time to time, he might just get back in the game to shut us up. And yes he is right and yes there are many rockers made with wrong geometry. Nice thing about factory coined rockers with their skidding ends is that you can't see these problems, the visability a roller tip rocker allows you to be come frightened by being able to see what's really going on and it often ain't pretty.

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