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Vacuum Advance Pipe Trick

In my effort to restore my 1960 MGA to stock, I acquired one of the original vacuum pipe assemblies, Moss #163-620, that goes from the vacuum unit to the rear carburetor. I intended to use this to replace the rubber tube/pipe set-up that was on my car. Of course, my vacuum unit is the newer type with a slip-on connection and the old style nut and compression fitting will not work with the new unit.

My goal was to install the original vacuum pipe so it looked as stock as possible. Here's what I did:

  1. Remove the rear spark plug wire and the heater hose on the heater valve to clear access to the vacuum unit.

  2. Use a die to put threads on the connecting end of the vacuum unit. I used a 10-32 die. Angle it carefully so it is perpendicular to the vacuum connection. To get a good grip on the die, I wrapped a fat rubber band around it (works for opening pickle jars too) and used a pair of heavy pliers to turn it. Thread the connecting end at least three-quarters of the way down its length.

  3. At the distributor end of the pipe assembly is a brass nut that is held onto the pipe with a compression fitting. The pipe slides freely through the nut, stopped by the ferrule. The interior diameter of this nut is too large for the connecting end of the new vacuum unit. Find another thin nut to match the hex size of the large brass nut (3/8"), and tap it to 10-32 to match the threads on the vacuum unit end.

  4. Hold the new tapped nut onto the end of the large brass nut on the pipe. Make sure the pipe still has room to move up and down inside the nut. You will need to screw the new nut all the way down onto the end of the vacuum unit in order to get a good seal, so the pipe may have to be cut to make space for the vacuum end, as it threads up into the nut. I used a jeweler's saw to cut the pipe without crimping it.

  5. Now solder the new nut onto the end of the brass nut on the pipe. I used silver solder and a small propane torch. Use only enough solder to mate the nut and fitting or you may ruin the threads in the new nut.

  6. Polish the new nut assembly and screw in place until the pipe does not move freely.

As an alternative to all this work, buy the rubber adaptor, Moss #371-805. You'll spend about four hours less than I did on this project!

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