Proper Technique for Adjusting Crane Roller Rockers for the LS Series Engines.
Written by Roger Vinci
We have had several questions from individuals installing our Crane Gold Race LS1 Rocker Arms about why we wrote the instructions the way we did. Our premise was that most of the time, these rockers would be installed on the engine with the engine in the vehicle. The most important of these considerations is that the stock LS1 valve springs have relatively low seat pressures (70# new and frequently 55-60# after 20-30,000 miles of use). Our instructions call for a procedure of turning the crankshaft 2 to 3 full revolutions, incrementally, and adjusting any loose rockers to zero lash. Here is where the confusion occurs.
Zero lash should be determined by carefully lifting up on the front of the rocker arm.. at the roller tip and letting the rocker fall against the valve stem. The loose motion, or lash, causes the rocker to click against the valve stem. The adjusting nut should then be adjusted clockwise, by finger, a little at a time, until the click or loose motion is just removed. Do not turn the nut any tighter for this will depress the pushrod into the lifter. When in doubt, back off the nut and repeat the procedure. When all 16 nuts have been zeroed, the engine must be rotated, from the crank pulley bolt, or with a strap wrench. I recommend rotating about 1/4 to 1/2 turn at a time. You will need to rotate the crankshaft a full six turns to ensure all of the rockers have cycled completely before you have finished the next phase of the procedure. When you check for zero lash again, you will see that some of the rockers are loose because the cam has rotated and those lifters have moved toward the base circle. Simply repeat the rocker arm lash checking and adjusting procedure again. Remember! Only tighten the nuts "by finger" on the obvious loose rockers, and only enough to cause the tip of the rocker to lightly rest on the valve stem. Next rotate the engine another 1/4 to 1/2 turn. Check lash and adjust again. Repeat the lash checking and engine rotating until you no longer have any loose "clicking rockers", you are finished with step one. Again, please note that sometimes the engine must be rotated several times before all the loose rockers are at zero lash. Now, that the "0" lash procedure is complete. you will not rotate the engine again. Step two requires you to tighten the adjusting nuts on all 16 rockers 1/4 turn. Wait about 5 minutes and repeat. That is, rotate the rocker nuts another 1/4 turn. Wait 5 minutes and rotate the nuts 1/4 turn again. You must rotate the rocker nuts, in this manner a full 1 and 1/2 to 1 and 3/4 turns, so keep an accurate count of the number of times you make 1/4 turn adjustments. You must wait 5 minutes between each 1/4 turn rotation to prevent the depressed valves from contacting the pistons. When you have finished the adjustment procedure, tighten the jamb nuts by holding the adjusting nut with your wrench and adjusting the Allen screw until it contacts the stud, with an Allen tool. Then rotate the tools simultaneously clockwise about 1/8 turn to complete the adjusting procedure. The Allen screw should never be torqued more than 20ft lbs. At this time it is a good idea to take a compression test to insure that all cylinders have equal pressure. A low compression cylinder probably has a rocker that is too tight. It is real easy, now, to readjust the rocker before installing the valve covers etc. All of this is necessary to allow the “relatively weak” stock valve springs to “bleed down” the hydraulic plunger in the lifter to allow proper lifter preload adjustment. If this procedure is not followed, valves could be “hanging open” when the engine is cranked over. This could result in bent valves. We realize that this procedure seems unnecessary or “overly-complicated” at first glance; but it works and, in the long run, minimizes installation aggravation. The use of higher seat pressure springs can reduce the waiting periods from 10 minutes slightly, during rocker arm installation. If the rockers are being installed as part of a complete rebuild, we recommend adjusting lifter preload to .060 -.100.” Extensive testing has shown this preload to provide the best power and performance, as well as minimizing valve train noise. When the engine is started for the first few times an audible clicking valve train noise may be heard. Run the engine for about fifteen minutes. Vary the rpms up and down during the procedure. After this run in time, the lifters, pushrods, and rockers should fill with oil and the noise will subside. The tech department at Crane will gladly help you through this procedure if issues occur. 866-388-5120
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