Valvetrain
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Roller rocker arms

Roller rockers are infinitely stronger than stock stamped steel rocker arms and are more resistant to bending and breakage under high spring pressures at high rpm. Stock pressed steel rocker arms are prone to failure in high performance applications. A high rate of fulcrum wear, flexing, cracking, splitting and breakage are common problems that will result in power loss or possible piston failure due to detonation of the incoming air/fuel charge. The traditional metal tip on standard rockers literally drags across the valve tip as the rocker opens and closes causing high side loading on the valve. This inside force leads to irregular and rapid valve, valve guide, and valve seat wear in many engines. The roller tip on roller rockers eliminates this side loading action.
The use of needle roller bearings at the rocker fulcrum combined with a roller tip at the valve greatly reduces horsepower robbing friction in the valve train to provide a measurable power increase over standard rocker systems. The reduction in friction with roller rockers has additional benefits of reducing the operating temperature and foaming effect of engine oil to provide a cooler running engine.
Unlike stock stamped steel rockers, roller rockers maintain a constant indicated rocker arm ratio throughout the full valve lift because the center line of the roller stays constant and only its contact with the valve stem center line changes.
Increasing rocker arm ratio (stock rockers are 1.6 ratio) increases the valve lift without having to change the camshaft. Using longer-ratio rockers typically increases engine torque and HP in the mid range. After you install longer-ratio rockers, be sure to check that the piston-to-valve clearance is adequate (minimum 0.040") before running the engine.
The use of high performance hydraulic or mechanical camshafts requires some form of valvetrain length adjustment to achieve correct clearance and geometry. Adjustable roller rockers allow these corrections to be made quickly and easily.
Yella Terra

1983-04 Jeep 258 & 4.0L Roller Rockers

5/16" Shaft Type Easy Fit (1.6 ratio) Non-adjustable YT6627
Installation instructions
Fit under stock valve cover

5/16" Shaft Type Easy Fit (1.7 ratio) Non-adjustable YT6628
Installation instructions
Fit under stock valve cover

5/16" Shaft Type Easy Fit (1.6 ratio) Adjustable YT6328
Edelbrock head requires modification
Mopar Performance

Part No. P4529885
5/16" shaft-type, easy fit, 1.6 ratio, adjustable
Cylinder head does not require any machining
Comes complete with a Hesco HESI6VCS 1/2" valve cover spacer necessary for additional clearance. Also requires Hesco Thermostat Housing Spacer #HESTHS to eliminate clearance problems when using a valve cover spacer.
Harland Sharp

Part no. CSP-S40196
1.6 ratio, non-adjustable, pedestal mount, 5/16" bolt.
Fit under stock valve cover. Easy bolt-on replacements for stock rockers.

Part no. CSP-S40196A
1.6 ratio, adjustable, pedestal mount, 5/16" bolt.
Requires a valve cover spacer and shorter pushrods for installation.
Crower

72848-12 Aluminium roller rocker arms AMC 6-CYL, 1.6 ratio, adjustable, stud mount, 3/8" stud
73648-12 Stainless steel roller rocker arms AMC 6-CYL, 1.6 ratio, adjustable, stud mount, 3/8" stud

Crower 88416-12 alloy rocker studs (5/16" base thread, 3/8" stud) required to mount rockers
Crower 70518-6 pushrod guideplates and Crower 70158-12 chrome moly hardened steel pushrods (9.625" stock length, 5/16" tube diameter) required to stabilize valvetrain



Lifter Preload

Stock pushrods are 9.625" long and have a tube diameter of 5/16".
Longer or shorter Crower chrome moly hardened steel pushrods are available to enable the correct lifter preload (0.020"-0.060") to be set when non-adjustable rocker arms are used. Shorter pushrods reduce preload while longer pushrods increase it:

69955-16: 9.550" long (-0.075")
69960-16: 9.600" long (-0.025")
69965-16: 9.650" long (+0.025")

As an alternative to installing shorter pushrods, the lifter preload can also be reduced by installing shims under the rocker arm bridges. The Crane rocker arm bridge shim kit 99179-1 includes two different thickness shims to decrease lifter preload by approximately 0.030", 0.060" or 0.090" depending on the combination of shims being used between the bridge and the cylinder head. Excessive preload may be caused by a camshaft change, valve job, head/block resurfacing, thinner head gasket. These shims can be a quick and easy alternative to resorting to different length pushrods. The kit includes 32 shims (16 x 0.030", 16 x 0.060") for V8 applications.