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Hardening 4140?

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  • Hardening 4140?

    I have made a double throw 1 piece crankshaft out of 4140 for an opposed twin 4-stroke. I would like to harded the crank pins (1/2"dia.) if it won't cause any problems with cracking or warping too much. Oil passages have been drilled in the crank, so it may not be a big deal if it can't be hardened.
    What's the best method to harden them? Is it difficult to just harden the surface?
    I did leave alot of material to be ground.
    Thanks

  • #2
    I'd pay more attention to the knife makers in this crowd than "us hillbillies"..

    oil quenching is what I do, anneal pack it in alum to suck the carbon out.

    A good knifemaker will tell you a color to bring the metal to ie: straw, dull yellow? Bringing "good" metal to too high of a temperature can actually ruin it's properties. Using a molten salt bath is the current trend.

    As a temper'er of metal I am a good electrician.
    Excuse me, I farted.

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    • #3
      I think you'll be hard pressed to do a successful hardening job on a piece like that at home. There are just too many ways it can warp and reasons for it to warp. BUT...
      if you want to try it, I'd heat ONLY the crankpins, one at a time, keeping the rest of the crank cooled off. Quench one crankpin, in oil, then heat and quench the other. Quench vertically, so the pin is cooled on all sides uniformly.



      [This message has been edited by SGW (edited 12-24-2005).]
      ----------
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie

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      • #4
        For that kind of job Some machine shop send 4140 to be hardened to specialised treating business. If they are willing to add your parts to the batch they do a better job than any homebrewmachinist can do. If they don't screw you up, the prices are reasonable.

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        • #5
          Your best bet is to find a 'Heat Treater' ans see if they an inducton harden the journals for you.

          Pat

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          • #6
            If it's a one piece crank you would nearly have to machine it oversize,treat it,straighten it then grind everything to the finished size with a toolpost grinder.That could be quite a chore.
            I just need one more tool,just one!

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            • #7
              <font face="Verdana, Arial" size="2">Originally posted by PhilR:
              I have made a double throw 1 piece crankshaft out of 4140 for an opposed twin 4-stroke. I would like to harded the crank pins (1/2"dia.) if it won't cause any problems with cracking or warping too much. Oil passages have been drilled in the crank, so it may not be a big deal if it can't be hardened.
              What's the best method to harden them? Is it difficult to just harden the surface?
              I did leave alot of material to be ground.
              Thanks
              </font>

              I never did a crank, but have done a lot of 4140 brake die tools. Stand the crank up to heat the end. You don't want the heat running to the crank body. Use oxy-acetalene, carborizing flame (white flame) to heat the areas to be hardened to a very dull red. Immediately hit the heated area with a bast from the air hose. After the crank cools to the touch polish to bright metal. Reheat with a neutral flame the hardened area (gently) until the end starts to turn dark brown or light blue. This will yield high 30 to low or mid 40 Rc. The lighter the color the harder. A light straw color might be 48 to 52 Rc, but this isn't really recommended because 4140 is really a strength as opposed to wear alloy. Dark brown to light blue should give the best results.

              Good luck and Merry Christmas

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              • #8
                Thanks for the replies.
                We are building some truck fender rolling machines at work, so it appears there is some parts going out for nitriding.(Not titanium nitride though. It's that black coating which has a hardness of about 70RC and is a few tenths thick). My boss has no problem with me sending the crank with everything.
                How well would this coating hold up in the cylinder bores?

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