lawnmower overhead valve adjustment

Most of todays modern engines above a 3hp have overhead
valvesand will need adjustment after about three or four
years of usage you will find out.
A common symptom will be that the engine will be hard to
start,or will slowly turn over as if the battery is weak or the
starter is dragging.This indicates the intake valve is closing
to soon,which means the rocker arm is to loose and must be
adjusted back to specifications,usually .003 of an inch.This
is done with a feeler guage and usually a 10mm open end
wrench and torx screwdriver of the right size.

Normally its the intake valve that wears out of adjustment
and causes the above symptom.
Valve adjustment is not that complicated, so if you try it
yourself and get into some sort of problem,usually the shop
can straighten it out in about 20 minutes.
Valve tolerances are .003 intake and .005 for exhaust for
most small engines Ihave came accross, at least briggs and
stratton.with overhead valves.Tolerances for engines with
valves enclosed are different.

To adjust you will need to remove valve cover,remove spark
plug,insert a screwdriver into spark plug hole,hold it straight
while you turn flywheel with your hand clockwise you will
feel piston pushing screwdriver out, as soon as you feel
srewdriver is all the way out.If you hold pressure on
srewdriver when piston reaches top of cylinder you will feel
screwdriver start downward.
Immediately stop turning flwyheel and turn back a little until
screwdriver is pushed back up,find the point when it is all
the way up and just a little turn of flywheel would start it
down

Now you have found what is called engine top dead center
and this is where everything is lined up to adjust valves.
Kohler engines usually are not adjustable,mostly briggs and
tecumseh and some of your japanese engines will give you
these valve problems.

Now with valve cover off,you will see the rocker arms.They
are similiar to rocker arms on japanese engines of four
cylinders or more.At top dead center where you just
positioned engine the rocker arms should be loose, but not
to loose.Take the feeler guage,open the blades out and find
the one marked.003 and insert it between the intake valve
and rocker arm,if it just fits,its within the tolerance,but if it fits
loose and there is a lot of play you will have to loosen nut on
rocker arm, and usually inside the nut is a torx screw that
you will loosen alsoand back out just a bit, now with feeler
guage between rocker and valve tighten nut until the feeler
guage is snug,but not stuck,that puts everything within
tolerances.
The exhaust valve is done the same way except you use
the.005 blade on the feeler guage.Note, if the feeler guage
fits snug, no adjustment is needed.Getting the engine to top
dead center as explained above is the most important part, if
it is not at top dead center you cannot adjust the valves
properly, because everything will be out of time.

Believe it or not a lot of four wheelers suffer from not having
the valves adjusted and the above tolerances will work on
them also, if the camshafts are not worn out.Usually a
tapping sound can be heard,overlly loud that is.