It's All in the Angles
Since our AFR heads were not as thrashed as originally thought, Grubbs started by machining the original 2.08/1.60-inch valves. Each valve was machined with a new 45-degree seat, and the valve tips were cut perpendicular to the seat, a step many machine shops overlook. The intake-seat angles are 37-45-60 degrees with a 0.035-inch intake-seat width since this engine was destined for fewer road miles and more track time. Grubbs says for a higher-mileage street engine, he'd recommend a wider 0.050-inch intake seat. Generally, as the seat width narrows, airflow improves.
On the exhaust side, the top starts at 35 degrees to the 45-degree seat then opens into the throat area with a radius cut. The exhaust seat is also ground to a 0.060-inch width, which is wider than the intake for better heat transfer, since the seat is the ideal path for heat to be moved away from the exhaust valve.
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If the valves had turned out to be junk, the best bet would have been a new set from compa
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JGM's Sunnen SGM-700 machine precisely cuts all three angles into the valve seat simultane
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This is what the new valve seat looks like. Note how the exhaust cutter also improved the
Peart checked each of the springs to ensure they were all within spec.
Assembly Time
There's more to assembling heads than just squeezing the springs between the retainer and the spring seat. To start off, Peart checked the valvesprings with their retainers to determine if they were usable. Valvespring load is an important variable when assembling a valvetrain, so the springs must be carefully matched to the cam. The existing springs were 1.540-inch-diameter dual springs that measured 115 pounds of load with the valve closed and around 350 pounds at 0.500 inch of valve lift with a coil-bind dimension of 1.150 inches. The coil-bind height subtracted from the installed height (1.940 - 1.150 = 0.790 inch) is the amount of valve lift available (minus an additional 0.050 inch for clearance). These are pressures that would work for a strong hydraulic roller or even a milder mechanical roller cam. Along with that, these springs are tall enough to accommodate up to a 0.740-inch-lift cam to be used with the 0.200-inch-longer valves, since a standard small-block Chevy installed height is generally around 1.750. After all 16 springs passed muster, we decided to reuse them along with their steel spring seats, which prevent damage to the soft aluminum heads.
The next step was to equalize the installed height, which turned out to be a tall 1.940 inches. We also noticed that eight of the 16 Crane roller rockers had witness marks on the inside radius of the rocker tip where the rockers had hit their retainers. This occurred because the valve-stem tip was sunk too deeply into the retainer. Instead of using a shorter retainer, Grubbs used a different set of Crane 10-degree locks that effectively pushed the valve tip up by 0.050 inch. This also will reduce the installed height, which became 1.890 inches and raised the closed-spring pressure by roughly 20 pounds.
Peart equalized the installed height between the retainer and the seat for all 16 valves using shims to get all the heights within 0.005 inch. The next step was to check the retainer-to-seal clearance, which was more than enough at 0.860 inch. With a 0.650-inch-lift cam, this still would produce 0.210 inch of clearance.
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The next step was to check installed height, which came out to 1.890, using a height mic t
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With the new valve seals installed, we checked the retainer-to-seal clearance, which was a
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We even went so far as to check the runout on the original rocker studs, since these were
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Here's the damage we found on 8 of the 16 roller rockers from retainer interference. This