Whether you use the stock ratio, or increase the ratio for more lift, it's imperative that the rocker arm fits the heads, clears your valve covers, and its geometry is properly set up to move the valve in the most efficient manner. If the rocker arm isn't checked and fit to the engine, you could induce several issues into your valvetrain, including excessive valve guide wear, rocker-to-valve retainer contact, piston-to-valve interference, damaged cam lobes, bent pushrods and more. While there is a lot to an engine's valvetrain to be considered, we're going to concentrate on the typical "bolt-on" setups, as in fully assembled aftermarket heads, or valvesprings being installed on existing heads that are specified/called out by the cam manufacturer's spec card or tech line. We simply don't have the room here to go through degreeing a camshaft, setting up valvesprings by opening and seat pressures, and so forth. If you're building a truly custom engine, your engine builder will deal with these measurements/adjustments, so for the gist of this story, we'll focus on the weekend wrench installing aftermarket heads or a new cam and spring kit and wanting to get their rocker arms and pushrods correct for their new bolt-on package.
There are two schools of thought when it comes to rocker arm geometry and pushrod length optimization. The easier, and more popular, method that Joe Wrench can accomplish at home during a cam swap, or even just upgrading rocker arms, is called the rollout method. The rollout of the rocker tip across the valve tip is measured and held to a minimum by changing the pushrod length. The second, more involved, method is called mid-lift method. It's also commonly referred to as half-lift centering. This method requires a dial indicator to read the valve's lift so that the midpoint of the valve's lift can be determined to allow measuring the geometry at the mid-lift point. Pushrod length is then determined to optimize this reading. Mid-lift measuring places the priority on centering the rocker tip over the valve at mid-lift. For all but the most extreme racing engines, or those who love to dabble in dial indicator measurements and check every single spec (twice) on their engine upgrades, mid-lift geometry checking is your bag. For the rest of us, you'll get perfectly acceptable results using the rollout method.
So, concentrating on rocker arms once again, why would you want to upgrade them in the first place? For starters, Ford, like many OE companies, used a basic stamped steel rocker arm on the majority of their engines. These stamped steel rockers do not have accurate rocker ratios due to the stamping process. Furthermore, the stamped rockers can flex under higher cam lift specs, effectively reducing the potential of that shiny new bumpstick you just installed. Lastly, the stock stamped steel rockers, often called sled or sliding rockers, have no bearings or roller parts to them to reduce friction, just a ball-type fulcrum to pivot on. The friction robs the engine of power and increases oil temperatures. If you're taking the time, effort, and money to install decent aftermarket cylinder heads, converting to a roller cam and lifter setup, or just want to bump up your stock cam lift a bit with increased rocker ratios, you'll be best served with a quality aftermarket roller rocker design. Most importantly, you need to set the rocker arm geometry and pushrod length accordingly.
8 b. Doing so for the average...
8 b. Doing so for the average home wrench turner means the only thing to really concentrate on is the rocket arm geometry and correct pushrod length.
9 This graphic from Comp...
9 This graphic from Comp Cams shows a profile view of your typical rocker arm, pushrod, and valvespring configuration. This allows us to easily see where there can be critical contact points with the various parts. You want to be sure you have at least 0.030-inch clearance between the rocker arm and the retainer at all lift points to prevent hitting the retainer, which can cause retainer/lock failure and a dropped valve. You also want 0.030-inch clearance between your retainer and valve stem seal; otherwise the retainer will tear your seal and cause oil consumption issues.
10 The key to proper rocker...
10 The key to proper rocker arm fitment/geometry is having the right length pushrod. While it's plausible you could try different length pushrods until you got the geometry right, it's much faster to simply employ an adjustable
11 Of course, if you have...
11 Of course, if you have a long enough pair of calipers you could also measure the adjustable pushrod in this manner as well.
12 Now that you have your...
12 Now that you have your adjustable pushrod in hand you can measure and determine the correct length pushrod for your particular valvetrain package and rocker arms being used. Place the adjustable pushrod in the lifter cup for one cylinder (intake or exhaust) and then coat the valve tip with a Sharpie or dry-erase marker.
13 Place your rocker arm...
13 Place your rocker arm onto the rocker arm stud without the lock nut. Turn/unthread the adjustable pushrod until the roller tip of the rocker arm is just inboard of the center point of the valve, and then secure the rocker with its lock nut finger tight. Rotate the engine several times via the crankshaft to produce a wear pattern on the tip of the valve.
14 Once you remove the rocker...
14 Once you remove the rocker arm, you should see a bright strip on the tip of the valve. This is the roller rocker arm tip's travel across the tip of the valve. The general rule of thumb is you want this strip to be 0.080-inch or less in width. Center the pattern on the valve tip and make the pattern as thin as possible by adjusting the pushrod length and measuring again as needed. Comp Cams tells us that the shorter the travel (width) the better, than being truly centered, and that it is best to favor the inboard side of the valve tip. Once you have an acceptable pattern you can measure your adjustable pushrod and order your new pushrods for the best geometry, performance, and longevity.
15 Once you have your new...
15 Once you have your new pushrods it's time to install them and adjust your rocker arms to button up the valvetrain. Rotate the engine until the exhaust lifter (on the cylinder you're installing) just starts to come up. At this point you can install the intake rocker arm and adjust it. Rotate the locknut until you reach zero lash (the pushrod seats in the rocker/lifter and you feel drag on the pushrod while rotating it), then rotate the locknut an additional 1/2- to 3/4-turn and while holding the adjustment, tighten the set screw down. To install the rocker arm on the exhaust valve, rotate the engine until the intake valve reaches maximum lift and is about halfway back down, then install your exhaust rocker and repeat the adjustment process. Work your way through the engine's firing order, or go cylinder to cylinder, whichever you prefer, to adjust all 16 rocker arms. An easy way to remember this is E.O.I.C. or exhaust opening, intake closing. Note: Mechanical cam lash is adjusted in the sam
16 Finally, if you’re using...
16 Finally, if you’re using shaft mount rockers, they will have adjustable pushrod seats and the adjustment procedures are the same, you’ll just be adjusting the pushrod seat via the internal hex screw and tightening the outer nut to lock the adjustment into place.