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  • How To Set Valve Lash

    To many racers and enthusiasts, the concept of valve lash is regarded as a dark art. It seems like some mystery craft that is best left to engine builders and mechanics. Yet, proper valve lash can actually be set by anyone. Not only is it vital to the health of your engine, proper valve lash may also give you an advantage on the track.

    Valve lash itself is the mechanical clearance in the valve train from the valve tip to the rocker arm in an engine setup that uses solid/mechanical lifters. Excessive lash will cause a great deal of noise in the engine and wear in the valve train, while lashing too tightly may hang open a valve, thereby not allowing the cylinder to run. Instead of making compression, air will blow through the valve. Thus, proper valve lash is critically important.




    To set lash, COMP Camsģ uses the method known as Exhaust Opening, Intake Closing (EOIC). This is just one method, although there are plenty of others. This process works on any pushrod engine.First, with the valve covers and spark plugs removed and the rockers on, screw the polylocks of the rocker arms until they are finger tight. Then, rotate the engine until the exhaust pushrod on the cylinder that youíre working on begins to move upward. As you rotate the engine you will be looking for any rocker arm movement. This is the process of exhaust opening. At this point you can adjust the intake because the intake valve will be closed, ensuring that the lifters are on the camís base circle. Should you adjust lash while the lifters are not in this position, you run a high risk of hanging open a valve.



    Next, place a feeler gauge between the valve tip and rocker arm. Tighten the adjuster nut of the polylock until the proper lash is found. When you get to your preferred lash, hold the adjuster nut in place and set it with the inner screw using an Allen wrench. The polylock adjuster nut adjusts the amount of valve lash, while the set screw locks it in to place. Finally, tighten with an adjusting torque wrench until it clicks at 20 foot pounds of torque. This tightens the adjuster nut to the inner set screw and ensures that they do not come apart. The lash on most engines is set anywhere 0.012 in. to 0.022 in. Check your cam spec card for exact valve lash settings.

    To set lash on exhaust, rotate the engine again and wait until you see the intake valve open to full lift and start to come back up. Again, simply watch for rocker arm movement. You can then set lash on the exhaust the same way as you did with your intake valve, and continue the process for the rest of the valves in the engine.





    Aside from setting valve lash to ensure optimum engine performance, some engine builders and racers also use valve lash as a tool for tuning at the track. Tighter lash gives an engine more bottom end torque, while more lash creates more top end horsepower, which is typically made in high RPM. However, lashing too tightly can hang open a valve, while excessive lash will decrease the duration of lift, in essence making a cam smaller. It is a fine line to walk, but one that may ultimately pay dividends.

    Valve lash can be set with a box end wrench and Allen wrench, but there are specialty items available to make setting valve lash easier. Visit www.compcams.com to find the Valve Lash Adjusting Torque Wrench, and, if you are setting lash with the engine in your car, check out www.powerhouseproducts.com to find a Remote Starter Switch that will help you bump over the engine.

    Ultimately, while setting valve lash may often be seen as a job that is only suited for a small percentage of people, in reality it is a relatively