A Simple Method for Making Replacement Needle Valves

| December/January 2000

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.


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