The aftermarket rockers are often used with a stud girdle. This usually consists of two parallel bars above the rockers that clamp around long adjuster nuts. The effect is minimized flex and stabilized rocker studs, resulting in the valve movement more closely following the cam design. With a stud girdle, the lash may change when it is tightened and loosened. This happens when the rocker studs are not in perfect alignment. So loosen the girdle, set the lash on the valves, and re-tighten the girdle. Then go back and check the lash. If any lash settings are more than 0.002 inch off from before, loosen the girdle and adjust to the variance.
I spoke at length with Mark Campbell, Crane Cams' director of camshaft and valvetrain research and development. He feels that one can spend too much time trying to get the lash setting to perfect accuracy, and that one or two thousandths doesn't make a real difference. We also discussed using lash setting to change cam characteristics. For instance, tightening the lash will advance the cam. Mark said this is an acceptable practice as long as the adjustment doesn't vary more than 0.007 inch from the original specs. If more adjustment than that increases performance, then a cam change is in order.
When To Set The Valve Lash
Set the lash when the cam lobes are pointed away from the lifters. In the absence of a clear glass engine block, we have to rely on the timing pointer on the crank balancer. There are other methods, but they all give a similar result. When the timing pointer points to top dead center (TDC) on the number one cylinder and both valves are closed, the cam lobes are pointing away from the lifter. Set both the intake and exhaust valve lash to the cam specifications.
Next follow the firing order sequence to find the next cylinder. It is a big help if the balancer is marked in 90-degree increments. If it is not, get a timing tape that goes on the balancer. After having found the number one cylinder's position, rotate the crank in the direction the engine runs to the next 90 degree mark. The second cylinder in the firing order will be in position to be adjusted. Do this through two complete rotations of the crank, setting the lash on a cylinder, each 90 degrees marked.
Bumping the engine over with the starter and trying to hit the marks can lead to frustration and the utterance of some ugly words. Try removing the plugs and using a long handle ratchet to turn the engine with the balancer bolt. If there is too much in the way to reach the bolt, such as a fan shroud, then try this: Put a V-belt around a crank pulley or the balancer. Tape it securely to a tube or strong stick. When pulled in the direction of rotation, it will tighten like a pipe wrench. Any way you do it, getting the cam lobe high point position away from the lifter is necessary to set the lash properly.
Use whatever method of adjustment is necessary for your engine type. Stock pinch nuts wear out quickly and stock rockers can have a groove that inhibits proper adjustments. Aftermarket roller rockers are good. Mark your balancer or wrap it with a timing tape for proper orientation. When using a stud girdle, re-check after tightening the girdle. Finally, get some practice and it will get easier with time.
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