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304 stainless for model engine valves??

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  • 304 stainless for model engine valves??

    An internet averse buddy is building a 9 cylinder radial-don't recall which one, he bought plans and is building from bar stock. Think bore/stroke is around 1"

    Valves will be roughly 1.25" long, .1875" stem, .4375" on the big end. Plans recommend "stainless steel", but don't specify an alloy. We're thinking 304 but could use some advice.

    Thanks,
    Scott

  • #2
    Valves

    21-2N and 21-4N are the stainless alloys typically used for valve applications. Carbon steel valves usually have a hardness of 35-55 Rockwell C, so a stainless valve would have to be of an alloy and temper to perform in a similar way.

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    • #3
      Originally posted by SVS
      We're thinking 304 but could use some advice.
      304 she's a whore, 303 she's for me.

      304 work hardens if you look at it, not much fun to machine especially something intricate like a tiny valve. 303 is free cutting and quite nice to machine. 416 is also free machining.

      gene may be spot on for the demands of full size, full service engines...outside of my area of expertise....but I think for a model you have a more latitude. I've used 303 for valves and as i understand it is common practice for model engines
      .

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      • #4
        Just as an aside, I make the valves for my engines two piece with the stem of drill rod and the head silver soldered on and then machined to size. This allows the use of suitable material for the head without the need and difficulty of turning a big chunk of material down to the stem size.

        And, 303 definitely.
        Jim H.

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        • #5
          JC- +1 in the two piece valve. Goes much faster in the long run.
          I also have put a couple of holes on the face of the valve and make a tool with equally spaced dowel pins to help lap the valves in.

          Sid

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          • #6
            I have made valves by both methods, machined from solid and fabricated by silver soldering the head and stems together. I have had good success with both methods. I use 303 stainless all of the time. There are some purists who would would make them as in full sized practice, by cutting, hardening and grinding. It all depends which way the builder wants to go. With miniature engines that only get run for demonstration purposes, in most cases, spending hours doing extra work is unnecessary, at least that is my opinion.
            My 302 v-8 engine has somewhere in the neighborhood of 50 hours of running time on it and I have never had to redo the valves or seats.
            gbritnell
            http://youtu.be/fRVYYtdhG_8

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            • #7
              Originally posted by sid pileski
              JC- +1 in the two piece valve. Goes much faster in the long run.
              I also have put a couple of holes on the face of the valve and make a tool with equally spaced dowel pins to help lap the valves in.

              Sid
              I just cut a slot with a small slitting saw and use a screwdriver to lap the valves.
              Jim H.

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              • #8
                From what I understand free-machining 416 is hardenable. But if people are already using 303 with success, it's probably not worth the effort.

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                • #9
                  Originally posted by gbritnell
                  I have made valves by both methods, machined from solid and fabricated by silver soldering the head and stems together. I have had good success with both methods. I use 303 stainless all of the time. There are some purists who would would make them as in full sized practice, by cutting, hardening and grinding. It all depends which way the builder wants to go. With miniature engines that only get run for demonstration purposes, in most cases, spending hours doing extra work is unnecessary, at least that is my opinion.
                  My 302 v-8 engine has somewhere in the neighborhood of 50 hours of running time on it and I have never had to redo the valves or seats.
                  gbritnell
                  http://youtu.be/fRVYYtdhG_8
                  The purists should make them out of 2 separate pieces. We used to make exhaust valves in the plant that I worked at and they were made in 2 pieces. The head was cold formed and the stem was just a piece of round stock. Don't know what the materials were. The 2 pieces were friction welded together. Both pieces spun at a high speed then pressed together until they were white hot, then the machine was stopped in an instant. Weld finished.

                  Brian
                  OPEN EYES, OPEN EARS, OPEN MIND

                  THINK HARDER

                  BETTER TO HAVE TOOLS YOU DON'T NEED THAN TO NEED TOOLS YOU DON'T HAVE

                  MY NAME IS BRIAN AND I AM A TOOLOHOLIC

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                  • #10
                    Thanks guys, I'll tell him 303 or 416 if he's really ambitious.

                    John had been doing all this intricate work on a 20"x100" 60's era Italian lathe. We went to a sale in December and he bought(stole) the nicest inch/metric 10ee I've ever seen....Needless to say his model making productivity has gone up tremendously.

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                    • #11
                      Anybody ever tried to use a drywall screw as a valve? The shape is about right and they're definitely not soft steel. Maybe they'd be no good at combustion temperatures, I don't know. I once made some air valves using them and it worked fine.
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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