Inexpensive Tips for Fuel Check Valve Replacement

Fuel check valve repair and replacement can be simple and inexpensive

| July/August 1979


It is a relatively simple machining operation to replace the valve seats with inserts as shown in this photo of an "Alamo" Blue Line cylinder head.

One item that I have found difficult to locate, and missing from many old engines, is the fuel check value in the fuel tank. This tube from the tank to the carburetor inlet served as the reservoir for the carburetor and needed a check valve to hold the fuel in the tube.

A new serviceable unit can be made quite easily. To make check valves you will need the following parts, available from your local automotive parts dealer. These parts are:

(1)  An inverted flare fitting, straight connector, 1/8" pipe to 3/16" copper tubing.
(2)  A 3/16" inverted flare nut.
(3)  A 3/16" steel ball.
(4)  A short piece of 1/4" copper tubing.
(5)  A pipe bushing, 1/8" to 1/4".

These parts need to be soldered in place as shown in the accompanying photo. In order to hold the 1/4" copper tubing in place over the 3/16" inverted flare nut while soldering, I drill a 1/4" hole in place of the 3/16" existing opening in the flare nut. The hole drilled should only be about 1/4" deep and not through the entire nut. The length of the copper tubing should be measured by determining how deep the check valve should extend into the fuel tank, usually about one half inch from the bottom of the tank. In order to solder the copper tubing to the pipe bushing it will be easier to solder if a shim is wrapped around the 1/4" copper tubing where it fits into the bushing. Be careful not to extend it up into the 1/8" pipe thread. After the soldering job is completed, shake the check valve to be sure the ball is free in its cage (the 3/16" inverted flare connector). The majority of these old engines used a pipe fitting on the check valve tube, where it entered the fuel tank. The connection from the 1/8" pipe thread bushing to the carburetor may be any standard tubing fitting, flare, inverted flare, or compression type.

An alternative method may be to use a carburetor needle valve and seat, as shown in the accompanying photo on the right. Grind off the outside or excess material to fit into the fuel tank opening.

Many old engines have become so rusted that it is difficult to grind the valves with any degree of success. Cylinder head and valves are exceedingly difficult to locate. The valve problem can be solved with a little extra effort. The first thing to check is the valve stem for wear and rust. If the stem shows extensive wear, or badly rusted, or the head of the valve has no margin left on the edge of the valve, it should be replaced. Note the badly rusted valve head, stem and lack of margin on the edge of the valve in the accompanying photo. At the left of this old "Alamo" engine valve is its replacement, a modified, discarded valve from a truck engine. If your old valve passed the visual inspection and appears serviceable the next thing to check is valve to guide clearance. You can check the clearance by shaking the valve back and forth when it is just off the seat. There should be very little movement. The movement is excessive if it moves more than 1/16". The clearance can also be checked with a micrometer and a pin hole gauge. However, a slightly excessive clearance may be corrected by Knurlizing the valve guides and restoring the clearance to proper clearnace, approximately .001 inch.