Lashing Out at the Animal: Setting the Valve Lash on Your Race Engine

by Robert Markiewicz in Maintenance & Repair
Originally published in National Kart News January 2007

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Though there are critics on both sides of the fence when it comes to the benefits of the new Animal engine, one thing that neither side can dispute is how much easier setting the valve lash is on the Animal. Anyone who has tried setting the valves on the Raptor will probably tell you that it is not their favorite feature of the engine. Not only is it time consuming, but it also requires special grinders to do the job. Plus, the Raptor requires the head and valve springs to be removed when a lash adjustment is required.

The Animal engine and most other Over Head Valve (OHV) engines only require a couple simple hand tools and a few minutes to successfully adjust the valve lash. Removal of the rocker cover and sparkplug are all that is needed to do the adjustment.

When you adjust the valve lash what you are doing is setting the mechanical clearance of the related valve train components. This clearance is either specified by the engine or cam manufacturer and is dictated by the design of the valve train. Because metal parts grow with heat from the running engine, their clearance is needed to prevent the valve fro being forced open and allowing air to escape on the compression stroke. Other factors that go into the lash specification are related to the manufacturer’s tolerances and the cam design itself. The reason for pointing this out is not because it really affects the average engine builder or racer, but more to show that a lot went into deriving this critical measurement. So keeping it at its specific setting will help maximize your race engines performance. There are two main factors that cause the lash setting to change; the first occurs if the engine or related components were taken apart, and the second comes from wear of the related components. If the engine is taken apart or has had the head, rocker arms, or side cover removed in the tech barn, a valve lash check and possible adjustment are warranted. The main wear component of the valve train is the valve face and the seat. The valve opens and closes at a rate greater than 50 times a second at racing speeds. This constant pounding of the valve against the seat causes the valve to recess into the head. This is not a lot, but when the valve lash is only 3 thousandths of an inch to start with, it doesn’t take much.