Fuller & Johnson Restoration Moves Forward

Peter Rooke makes progress on his 1917 1-1/2 HP Fuller & Johnson Model N with fuel mixer, igniter and muffler fixes — Part 3 of 4.

| August/September 2014

This is the third in a four part series on Peter Rooke’s restoration of a 1917 Fuller & Johnson 1-1/2 HP Model N. Read part 1, part 2 and part 4 for the full restoration process.

Fuel mixer

The stem of the fuel mixer was broken off, leaving part of its threaded end stuck in the cylinder head. I stripped down the mixer and cleaned out the inside before squaring up what was left of the thread and recutting it with a 0.750-inch NPT die. There was not enough thread length to refit the mixer using this short section of new thread, as the large head on the fuel adjustment needle would rub against the cylinder head. I had to make an extension collar to screw onto the remains of the mixer and then into the cylinder head.

I placed a length of 1.250-inch diameter steel in the lathe chuck and drilled through with a 0.750-inch drill to a depth of 1.40 inches. I turned 0.750-inch of this length to a diameter of 1.050 inches before cutting a 0.750-inch male NPT thread on it. I started this thread using the threading tool on the lathe before finishing off with a die. I cut this bar to a length of 1.30 inches and reversed it in the chuck.

Next, I screw cut a 0.750-inch NPT female thread to a depth of 0.340-inch to match the length of the remaining thread on the mixer. I bored out the remainder of the new collar to 0.80-inch to match the bore of the mixer tube. I trial fit both parts to ensure that the mixer was correctly aligned in the vertical when screwed in tight. I also made a check to ensure that it did not foul the pushrod. This showed I needed to lengthen the lathe cut thread by 0.010-inch to ensure the mixer lined up correctly.

Once the fit of the new extension piece was correct, I rounded any rough edges with a file and then fit it to the mixer, using Loctite to hold it in place. I covered the part of the new thread that fit in the cylinder head with tape for protection and later, when all work on the mixer was finished, I rusted the collar and any exposed thread on the mixer to match the original using reverse electrolysis (learn more at Reverse Electrolysis Primer).

The tip of the mixer needle was badly worn and pitted so I had to replace it. It was difficult to measure the old taper, and I found I also needed to recut its seat. I used a 40-degree included angle for the new needle. After measuring the length of the old needle, I sawed off the corroded one and drilled a 0.1875-inch hole in the threaded section of the head.


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