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On these OHV engines the cam has a ~0.010 lobe to keep one valve slightly open during the compression cycle for compression release and easy starter cranking. Since this is a lobe on the cam and not a "slide out of the way lever" design used on other engine brands, this means that one valve (on mine it is the intake valve) is slightly open for all or most of the compression cycle at all times. This seems like a less than efficient design but it apparently works. The open valve has an aluminum push rod to compensate for thermal expansion differences between the aluminum housing and head and a steel push rod. With a steel push rod at this location the valve gap would open on engine heat up and compression release on a hot engine (and easy cranking) may not occur.