That looks, to me, like a joint that is dependent on a critical metal to metal fit. Any manual polishing might reduce the fit. I wonder if there are old tools that were designed to cleanup those surfaces to factory specs. I am surprised that the added lead or copper seals did not help. Thinking outside of the box ... 1)Maybe there are micro cracks. 2)Try a plastic bag, with a hole for flow. Temporary fix for testing. I do that with alcohol bottles to reduce evaporation. That will form easily to the seal shape. Include the threads.
I would clean each surface with 2000 grit emery paper, then use grinding paste on each surface (not the threads) and move them against each other (about 200 times). This is to make a face to face join without blemishes. If that doesn’t work, I would paint the receiving face (avoiding interfering with fuel flow) with high temp. thread sealer. Tony
Duane, I was thinking along the same lines as Tony. Take the upper section of the union off so you can rotate it freely against the lower section and use some fine valve grinding paste to polish up the two faces.
Leakage is very minor after using the viton washer, I like the idea of valve paste, has been a couple times where that would have been nice to use. Wish I had the tools to seat and face valves, I did the valves years ago on a Ford engine. Thank you for the ideas. Duane
+1 with Tony and others who said unions are a metal to metal seal. Thus they need to be clean and straight. If necessary lap the parts so they mate well. Lubricant on the ring threads will help it not bind while tightening. It takes a lot of torque to tighten it enough. IMHO a washer or sealant on the mating surface will cause the union to distort and make it worse.
@IvanN, good idea about lube on the threads, maybe the faces too. You can easily tell it is binding, jerky action. Duane
I would try @Tony Press idea using very fine grinding past(toothpaste can sometimes work) on both mating surfaces then assemble the joint using the nut so that the joint is just able to be turned freely, then rotate the joint much like you would lapping engine valves. The joint matting surfaces hopefully should seal using that process. You may have to repeat the process. If the joint is too damaged, try some exhaust cement and then making sure the joint has been firmly tightened in position, carefully heat it(otherwise you could de-solder the fitting) to cure the cement . Hope that helps. John
I thought I would first try lubricating the faces and threads, no binding, but still leaks. Even the viton washer after sitting the last few days leaked. Next I can get some valve seat paste. Did run it long enough to melt the pot of lead, but had to wipe the leakage away every minute or so. Duane
That type of fitting is more or less the same as used to connect a regulator to a high pressure gas cylinder. They are metal to metal seals and any scratch, hair, dirt or dust will compromise the fit. As suggested above, clean both surfaces with wire wool / very fine emery paper until there are no scratches / dings. No washer should be necessary. Regards John
I had high hopes, but no luck, even snuggling up the nut as I proceed, I can see both sides are shiny, but still leaks. Thank you everyone for the suggestions. Will try some more later then put it away. Duane
I wonder if you have a tiny leak elsewhere near the matting surface but not on the matting surface itself. A high temperature sealant may work.
I have a third furnace coming in the mail today, second model like this one, it was only $25 USD plus shipping. I have ordered a reducer so I can (maybe) at least connect the burner to the valve and at least save the valve. Only variable is the nipple from the new part to the burner which I should be able to change if needed. Nothing was working from suggestions here, so asked the Coleman folks and their suggestions failed too. I tried tinning one side of the union and that did not work. Since I have the reducer 3/8" X 3/4" ordered, I may secure parts, mark location and solder the parts together. Duane
I ended up fixing today after a few attempts. Soldered the top piece that completes the union, then noticed a vertical crack in the nut that binds that piece to the top of the valve. May have developed over the course in attempts to tighten the pieces. Ran a solder bead down the side, don't know how well that will hold. Do have a brass reducer on order to use in place of the top of the union. Need to purge the genny again as the flame goes out constantly now. Duane
