A Simple Method for Making Replacement Needle Valves

By Staff

R.R. 2, Box 1, Site 7, Carvel, Alberta, Canada TOE OHO

A problem frequently encountered in old engine restoration is
that the needle valve has been damaged or broken off or is missing
altogether. A great majority of mixer needle valves are threaded to
?’ either NF or NC. Threaded stock (Redi-Rod) in ?’ size,
both NF and NC, can be obtained for a nominal sum from bolt supply
or specialty hardware stores.

Measure the distance from the needle seat to the outside of the
mixer body using a piece of wire for a depth gauge. Cut a length of
threaded stock about 1?’ longer than the foregoing to allow for
tapering, the spring, the knob attachment and probably an
‘oops.’ Mount the piece of threaded rod in the chuck of a
1/8‘ or ?’ drill (it doesn’t
matter if the threads held in the chuck get ratcheted). Clamp a
length of 1 x 2 or angle iron to the grinder table at a suitable
angle to provide a guide for tapering the needle against the side
of the fine grinder wheel; the actual angle of the taper is not
overly critical but the taper should be about twice as long as the
diameter. Form the taper by running the rod in the drill against
the side of the rotating grinding wheel. The drill can be hand-held
using the clamped bar for a visual guide. Be patient-do not grind
too much material at a time or the point will burn. After the taper
has been satisfactorily ground, it can be polished by running it
against very fine emery or sandpaper (about 300 grit). On most
needles there is a length of smaller diameter immediately behind
the taper; this can also be formed on the grinder by running the
rod very carefully against the face of the wheel. It is a good idea
to do a couple of trial and error fittings into the mixer body to
get a size that just fits without binding. It is often necessary to
first run a ?’ tap into the mixer body to clean the
threads.

Once the needle has been formed, run it into the mixer body by
hand to get the final length, which will include the length of
extension required to accommodate the knob and the spring
available. Drill a vertical hole, equal to the length from the
point of the needle to the base of the knob, in a block of wood.
Place the needle in the hole and slide the knob over the extending
threaded rod; this will keep the knob perpendicular to the needle.
A heavy fender washer makes a good knob; it can be sculpted along
the rim with a hand grinder and given a guide mark with a cold
chisel. Fasten the knob to the needle by welding or other suitable
means such as brazing, metal epoxy or even soldering. (Don’t
forget to put out the fire in the block of wood.)

Finally, grind off any spatter or excess length, put the spring
in place and install the needle in the mixer body. Given a couple
coats of paint, your replacement needle valve will be hard to tell
from the original thing and should work equally well. One thing to
keep in mind, of course, with any needle valve adjustment is to
never run the needle down hard against the seat-stop turning as
soon as the slightest increase in pressure is felt.

Gas Engine Magazine
Gas Engine Magazine
Preserving the History of Internal Combustion Engines