Inexpensive Tips for Fuel Check Valve Replacement

Fuel check valve repair and replacement can be simple and inexpensive


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.

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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.

If there is excessive clearance, over .005, or about an 1/8" movement of the valve the next step is to replace the valve and ream the guide to fit. It is not necessary to buy serviceable valves. They may be obtained as discards from any local garage.

We should know something about valve stem diameters first. Common valve stem diameters are:


Common Fraction










10 MM







The sizes obviously vary as much as .004 from the size given.

The valve head diameters are relatively easy to measure and locate. Check your supply of old valves by measuring either the stem diameter or head diameter first. Sort them and then select the right valve for the engine you have. The head diameter does not have to be accurate closer than 1/8" or possibly 1/4" oversize.

After locating the replacement valve you wish to use, the next step is to ream the valve guide to fit the new valve stem with the proper clearance. If you have access to this equipment you can do the job. As a suggestion, I would check with local high school automotive shops or career center shops that might do the work for you.

After the valve guide clearance has been repaired the valve stem must be cut to the right length. Measure the old valve and grind the replacement valve to the proper length. Note the valve in the photo with stem ground slightly on one side so it can be center punched and drilled. The stem end can be drilled with an 1/8" drill. There is a trick to it, however, you must have a sharp drill, a drill press, and slow speed. You cannot ignore any of these items. I find it necessary on some drill presses to stop and start the drill motor while applying pressure to make it turn slow enough. Obviously the valve stem had to be secured in a vise or "V" block. A cotter key can replace any of the old style keepers on the valve.

After the valves have been ground and the valve guides reconditioned, the valve seat may be ground. This may pose a problem, too. The seats may be so wide and rusted that the valves seat below the cylinder head surface. Your local automotive parts store has the answer to this problem too. Replace the valve seats with an insert. Inserts are available in any diameter needed. They are even available in .015 or .030 inch oversize. Determine what size you need and have the insert installed. This job is a little tricky and you may want the auto parts store machine service to do it for you. You may also discover that the career center automotive shop may be able to do it for you. Keep in mind, the order of servicing is important to the extent that the valve seat must not be ground before the guide is restored.

Contact Bud Motry at 20201 Arthur Road, Big Rapids, Michigan 49307