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How To: Exhaust Pipe Nut

October 4, 2012


The fun part about restoring old machines is rebuilding or recreating items.  That should be clarified a bit better:  I think that it is fun to make replacement parts.  Your mileage may vary.  But the latest project in the shop, the 1913 Veloce, has given me a lot of opportunity to make parts.  The nut that holds the exhaust pipe onto the cylinder head needed replacement, due to numerous abuses by previous owners who possessed hammers and screwdriver-chisels, but who didn’t have the correct wrench to fit the grooves in the nut.  99.75 years of moisture hadn’t been kind to the steel either.

veloce exh nut 1

As you can imagine, some parts for early machines are available from vendors, but many are not. I couldn’t find this one didn’t from the limited sources.  But I already had a $3 bar of steel and all the necessary tooling, so I went about making one on a Tuesday afternoon.


veloce exh nut 3This is Step 3: setting up to cut the six 3/16” grooves in the outer edge of the nut.  Step 1-2 aren’t shown, but they were to turn the part to the correct outside diameter, drill a 1/2” hole in the center, and pressfit a 1/2” rod into the part.  That rod was gripped in the spin indexer, which is a cheap and simple way to rotate a part by any number of degrees on a mill.  You can get them for about $45 on sale from Enco, MSC, etc.


veloce exh nut 2

This photo shows the part, the spin indexer and the milling cutter.  The part was held in the vice, one groove was cut to half depth, then the vice was opened.  The indexer was indexed 60 degrees, and repeat.  Another repeat set of cuts to the full groove depth and we were ready to get back on the lathe.

  veloce exh nut 4

Step 4:  bore for the internal threads.  I use an end mill in the tool holder when boring a lot of material, it is more rigid and faster than using a boring bar.  The paint pen marks on the part and chuck jaws are used to mark where it fit in the 4 jaw chuck.


veloce exh nut 5

Step 5:  Cutting the threads.  I have a new favorite tool, this ID threading tool holder.  The carbide tool is formed to a 60 degree triangle, just like a male thread.  There are three faces, so the tool can be removed and rotated if the cutting edge breaks.  Previously I used carbide boring tools with a thread form ground into the tip, but they were fragile and more expensive than one of these 3x tools.  This toolholder will pay for itself pretty quickly.  I don’t recall the thread diameter, 1.9something inches with 24 tpi.


veloce exh nut 6

The exact thread diameter wasn’t terribly important to me, since I could check the fit with the mating part –in this case it was the cylinder head.  Doing this makes threading jobs on the lathe go much smoother.  Machining to a print showing the dimensions is great, but old parts can be tough to measure and draw, and ultimately all that I care about is the fit to the part, not if it was exactly a nominal dimension on a drawing print.  The remaining steps aren’t shown, but they were to cut the part to length, face the cut side, and chamfer and then round over the external edge.


veloce exh nut 7No more hammers and chisels to tighten and loosen the nut.  This adjustable spanner wrench was a few bucks at a flea market 10 years ago.  They are also for sale new from various tool vendors.  This type has a flat end, there are also types with pin ends for that type of nuts.


veloce exh nut 8

Comparing the new and old nuts.

Now ready for deburring, polishing and nickel plating.


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9 Comments leave one →
  1. Rick Yamane permalink
    October 4, 2012 8:55 am

    Nice job Pete. Cutting threads is a intimidating task for a lot of folks. Female threads intimidate me.

    • October 4, 2012 9:20 am

      Hi Rick. Single-point cutting of threads can be a bit scary. But if you double check the setting for the tpi, and only cut say .005″ per pass, it goes ok. The hardest part is stopping internal threads up tight against an inner shoulder. I stop the lathe short of the shoulder, then use the Jog power button on the lathe to bump it around the last few turns.

  2. Doug Lyon permalink
    October 4, 2012 9:13 am

    Beautifully done! I had the one I made for the Precision in and out of the chuck half a dozen times as I didn’t think to allow sufficient material to do what you did. I’m sure I could hear my old metalwork master grinding his teeth as I did it! I also took out the first thread by the flange to allow a little wiggle room on the pipe flange as I found it really pinched it up when tightened and it would jam a little, especially on the pipe seam. Only fellow sufferers can appreciate the hours that go into something apparently simple like that! Well done!

    • October 4, 2012 9:24 am

      Hi Doug. It is very satisfying to make a part, even if it looks simple when it is done. I’m sure that a local CNC machine shop could have done this for me, at say 1 hour or shop time and maybe $150. But it is so rewarding to do it myself. Plus I know that it fits perfectly and I learned a little bit in the process. BTW, I’m still finishing up the bike. If all goes well, and I earn enough $$ this fall/winter, I hope to see you with the Veloce at Epsom Downs in March for the Pioneer Run.

  3. Jim Abbott permalink
    October 4, 2012 9:23 am

    The old nut looked fine to me… Jim A., Tucson, AZ

  4. Bob Braun permalink
    October 4, 2012 9:44 am

    Time to hone my machining skills or develop new ones. It is pretty neato to be able to make an exhaust nut in one’s shop.

    I have ( slightly ) damaged a few thread-in Ducati 350 exhaust nuts in my early days. Later I figured out how to use a pipe wrench over a heavy leather ex-hippy belt to protect the fins and turn the nut. Worked great. A proper wrench would have been better but I had never seen one except as a picture in the manual. At least I had a manual.

    Your article is a keeper.

    Bbo in Canada

  5. John Quirke permalink
    October 7, 2012 11:10 am

    Well done Pete. It’s another road I have been down in front of you so I can appreciate the time and patience involved. Who knows I may even be at Epsom Downs again this comming year with you. Have you got your Pioneer cert yet

    • October 7, 2012 6:32 pm

      Hi John. No Pioneer Certificate yet. I was hoping to finish the restoration before I applied with the Sunbeam Club, but I’ll probably just send them photos of the bike being half-finished.


  1. How To: make an exhaust pipe « Occhio Lungo

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