Lapping Valves
This is no substitute for properly grinding valves and seats by a good
machine shop, but this procedure has proven useful to me on quite a few engines that
were being worked on for other reasons. I hope it works for you too.
Usually the valves are just lapped to insure that they seal as well as
possible. In cases where the seating surface shows some wear, I grind
the valves in a lathe first, but often it isn't necessary.
A close up of the head on the flexible shaft tool post grinder.
This is the most important part of this technique. Driving the valves
for lapping. Anyone who has ever had to do it with the silly suction
cup thingies they sell for this job knows how useless they are. In the
foreground are some special washers that are shop made. They are thick
ones with a hole smaller than ¼". A ¼" screwdriver bit is driven
through the washers to broach them out to a hex shape. Then they are
filed flat. Note also the spring in the left foreground. The washers
are arranged in the same pattern as the valves they will be used on.
the smaller ones on the exhaust valves. I should also mention that the
valves were inserted deeper into the wooden block when they were
cleaned up in the blasting cabinet. This keeps the stem surface in the
guide from getting marked. A wire wheel will do the same job, but
slower. The wooden block assures that the valves will go back in the
same locations.
In this picture, the washers are attached to the valves with "Crazy
Glue"!!! Don't worry. they will pop right off when the job is finished.
In the foreground are some of the things that will be needed.
Same as above from different angle. It shows the spring, two different
grinding compounds that are available from NAPA or others, a handy
container for the compound (the bottom of a beer can), and a Q-tip
applicator.
This is my favorite driver. In use it is reversed often. The spring is
slipped over the valve stem to lift it off the seat each time the
direction is reversed. The compound may have to be replenished several
times as it wears down. ( A valve and seat makes a good mill for the
abrasive) The process is finished when the seat and valve both show a
uniform dull finish in the contact areas. Use very light pressure to
lap and clean up well afterward. You can't be too careful with the
cleanup!
A close-up of the driver. with the screwdriver tip installed backward
to drive the washers. If the washers don't pop off easily, use a little
heat and they'll give up. Excess force could spring the stem.
