Don Terrill’s Speed-Talk

Thanks for replies guys. It is a 4580 rocker Paul and yes my understanding is that the b/t 3.6 is the same cleveland angles. We purchased valves to match our spring and cam requirements however looking at the rocker geometry now it will not work with midlift 1.8.

Steve.k wrote: ↑Thu Nov 14, 2019 9:12 pm...It is a 4580 rocker Paul and yes my understanding is that the b/t 3.6 is the same cleveland angles. We purchased valves to match our spring and cam requirements however looking at the rocker geometry now it will not work with midlift 1.8.

If I recall correctly, that rocker arm is designed for an 18.5* valve train angle. And while I cannot be 100% positive I think the 351C has 11* & 13* valve train angles (or somewhere very near that). All that being said, as far as I know the MEI 4580 rocker arm is the stud rocker that is nearest in having "correct" design geometry for the Cleveland...that is to say, more than any stud rocker of which I am aware for that cylinder head.

But because of the technical conflict between the 4580 rocker arm's design geometry relative to the 351C's valve train angles, the "Measuring Face" atop the rocker body cannot be utilized in this 351C application since the valve train angles are not in tune with the rocker body's Measuring Face as engineered. And so, utilization of the 4580's Measuring Face during installation of the rocker arm on the 351C valve train will not result in Mid-Lift geometry. Instead you must forego use of the Measuring Face and just rely on sight-of-eye (aka "eyeballing"), or draw that silly line from the trunnion-to-roller axle and also from trunnion-to-pushrod cup.

I'll bet that when you find the sweet-spot (ie, the best compromise for the 90* on both the valve side and the pushrod side), you will end up with a much shorter purshrod, and also a lot more rocker slot clearance for your adjuster/polylock. (In fact, at Mid-Lift your adjuster/polylock should end up closer to the center of the rocker slot). Lastly once this is all said and done, let the roller wheel rest wherever it may since its position has nothing to do with valve train geometry nor excesive "side loading" (the roller wheel on the rocker arm's tip was actually put there in place of the shoe so as to minimize side loading and help hold ratio steady throughout rocker arm articulation).

This comparison shot attached of 351-C vs BBC rocker arms on a common shaft may help. Note way-different rocker arm angles at the valve in spite of the BBC rocker being 1.70:1 and the Cleveland being a very close 1.73:1