These shims can be a quick and easy alternative to resorting to different length pushrods. Excessive preload may be caused by a camshaft change, valve job, head/block resurfacing, thinner head gasket. 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. Shorter pushrods reduce preload while longer pushrods increase it:Īs an alternative to installing shorter pushrods, the lifter preload can also be reduced by installing shims under the rocker arm bridges. Longer or shorter Crower chrome moly hardened steel pushrods are available to enable the correct lifter preload (0.030"-0.060") to be set when non-adjustable rocker arms are used. Yella Terra YT6626 High Performance Roller Rockers for 83-02 Jeep CJ-5, CJ-7, CJ-8 Wrangler YJ & TJ with 150c.i. Stock pushrods are 9.625" long and have a tube diameter of 5/16".
Adjustable roller rockers allow these corrections to be made quickly and easily. The use of high performance hydraulic or mechanical camshafts requires some form of valvetrain length adjustment to achieve correct clearance and geometry.
#Jeep 4.0 l yella terra rockers install#
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. Using longer-ratio rockers typically increases engine torque and HP in the mid range. Increasing rocker arm ratio (stock rockers are 1.6 ratio) increases the valve lift without having to change the camshaft.
#Jeep 4.0 l yella terra rockers full#
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. 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. 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 roller tip on roller rockers eliminates this side loading action. This inside force leads to irregular and rapid valve, valve guide, and valve seat wear in many engines. 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. 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. Stock pressed steel rocker arms are prone to failure in high performance applications.
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.