HANDS ON
HINTS FOR HOMEBUILDERS
A classic stuck exhaust valve: Notice the rocker arm is not touching the valve stem,
and the valve is stuck in the open position. This open position kills the power in
that cylinder, and that is 25 percent of the power of the engine, which makes a lot
of difference in a small four-cylinder Continental.
Stuck Valve Fix
BY BARRY DAVIS, EAA 389226
SOMETIMES CALLED “MORNING SICKNESS,” a stuck valve is nothing to
fool around with. Usually the first signs show up in the morning or
the first crank-up of the day when everything in the engine is warming up at different rates. Sticking valves never get better and won’t
cure themselves. A classic stuck exhaust valve will remain open, killing the power to that cylinder. There are a couple of ways to fix this,
one of which is to take the cylinder off and have it overhauled.
Another is to pop out the valve, clean the guide of built-up carbon,
and then replace the valve. It is easy to do and can be done quickly.
With the spring compressor in place and the bunched up rope holding the valve in place,
compress the springs and remove the valve keepers and springs.
First take off all the spark plug wires and
all top plugs so the engine cannot fire, as you
will be in close and moving the prop. With
that cylinder on top dead center, slide the
rocker shaft to one side and remove the
rocker arm. Remove the spark plugs from
the stuck cylinder and turn the prop so that
the piston is farthest away from the valve.
Start packing small rope into the cylinder (it
could take 12 feet or more), then gingerly
turn the prop so the rope is jammed up
against the head of the valve. This will pop
the valve out of the stuck position and keep
the valve from moving in while you are
compressing the valve springs and removing
the valve keepers. Don’t force anything!
I fabricated a simple tool from 1/4-inch
threaded rod and some angle iron I had
lying around the shop. Thread the rods into
the screw holes normally used for attaching
the valve covers and use a couple of nuts to
keep the angle in position. Use an old-fashioned valve spring compressor and
compress the valve spring to remove the
valve keepers. Remove the valve springs and
set aside, keeping the orientation in the
correct position.
