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Piston Expander. "Koetherizer"

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  • Piston Expander. "Koetherizer"

    I posted this on "another"forum in response to others and thought it might prove interesting on VFF
    "I have a piston expander called a Koetherizer. Invented by Emil Koether in the Early 1930's. You clean the piston internally by blasting with walnut shells in the right hand chamber of the machine. Then insert the special squeeze bolt through the gudgeon holes, tighten the bolt against its ballrace thrust washer and nut, squeezing it until it has expanded to the size you want across the thrust faces, using a micrometer across them. Up to 0.005 to 0.007 and maybe more can be gained depending on the design and weight of the piston. Then put the piston, still under compression with the squeeze bolt in place, into the steel shot blasting chamber and blast all around the inside, using the automatic piston rotator mechanism to blast every part at about 100 psi with compressed air and steel shot. This relieves the compression stresses in the aluminium alloy, so the piston holds the new shape and size after the squeeze is removed. The original operator who did many thousands of piston still comes to relieve new modern racing pistons for friends who race modern cars, for better longevity at high revs. Mainly as a favour to old friends. There was a category “piston expansion and automotive” in the NZ classified ads years ago in the newspapers, that dealt with Koetherizing and “micropeining” using tiny swinging hammers inside pistons. Koetherizing was said to be more gentle and kinder to pistons.
    SAJ in NZ
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    Last edited by SAJ; 03-07-2019, 03:46 AM.
    SAJ in NZ

  • #2
    That is quite the thing I have never heard of anything like this myself thanks for sharing this info.


    • #3
      That is pretty wild.
      I suspect a piston knurling machine would end up with similar results
      Wonder how the Koetherizer kept the pistons cam-ground or round, whatever the case was


      • BNCHIEF
        BNCHIEF commented
        Editing a comment
        That would be quite interesting to see in action for sure wonder if George Miller knows about these?

    • #4
      No this is some thing new to me never heard of one.


      • #5
        I have seen this done years ago by very few extremely talented and experienced professional senior vintage mechanics.

        My Uncle did it to one of my Model A engines in 1958.

        I heard it was common practice years ago, even prior to the much later Model A's. So much done back then that was never written nor heard of today.

        Worn split skirt Model A pistons were placed in respective Model A engine cylinders and moved sideways to check for gap clearance.

        Next the bottom halves of piston skirts, (below the bottom of the circumference of the wrist pins), were carefully reopened with the wedge point of a screw driver and retested in the same cylinder.

        Below is just one U. S. Patent for one type of tool.

        Control click on Download PDF to see where just this one patent was filed in 1934.

        A few other similar type U.S. Patents for expanding split skirt pistons were also granted later.


        • #6
          KNURLING piston skirts is very common & holds oil in the Knurling.
          Dad & Dog


          • BNCHIEF
            BNCHIEF commented
            Editing a comment
            True and what i know about.

        • #7
          Before and after the above no. 5 reply 1934 piston expander tool, with accompanying U.S. Patent number US2167287, there were several other piston expanders designed.

          Filed in 1928:

          Filed in 1933:

          Filed in 1940:

          Lots of vintage automotive shops expanded worn and slapping pistons in the 1930's and during WWII when money was tight and labor was much cheaper than parts.

          Also, not heard of or recommended today, when one had a smoking oil burning engine, carbon began to build up in ring grooves to where rings would not expand and contract with up and down movement within the worn tapered cylinders ....... lots of bypass and smoke when rings were stuck in the closed position at the top of the cylinder with a larger diameter.

          It was cheaper to remove rings, clean out carbon, reassemble and get a few thousand miles before buying new rings and/or re-boring and/or obtaining new pistons.

          When Model A restoration hobby began much later, times were much different where many could afford buying and paying for one or more extra hobby cars and purchase new rings, pistons, and other parts ...... the old former vintage ways of the "One Make-Do Car" were all cast aside and forgotten.
          Last edited by H. L. Chauvin; 03-08-2019, 12:40 AM.


          • #8
            Dave, the Koetherizer piston is cammed whether or not it started out as round. This is unlike knurling, which can leave residual stresses in the skirt. What method is best I have no idea, but I am aware of many hundreds of engines running around with pistons expanded about 0.005 on my machine. Coupled with the expansion is often a honing to restore roundness in the bore and removal of the ring ridge.
            I will definitely use it myself on the next engine I do - almost no skill is involved one you have watched a few dozen done. Just an ability to mike- up, maybe turn out and shim ring grooves, and possibly resize gudgeon holes if required on really worn subjects.
            my spelll chequer repeatedly changes "gudgeon" to "bludgeon" which looks hilarious!
            H L it resizes non split skirts as well as split. Only one of your 3 tools seems to do this. I have not seen the hand tool that forces lines into the skirt, but I have several roller burnishers to do the same job while the piston is still in the bore but each has only a limited size range in adjustability. And again they leave residual stresses in the alloy. One of the other properties of the Koetherizer is sress-relief in a new piston without re-sizing it, which is what the racing boys are after.
            SAJ in NZ
            SAJ in NZ


            • #9
              SAJ really appreciate the info here amazing how much one does not know having been around old cars and racing.


              • #10
                Looks just like a regular frumsteader to me
                28 Tudor
                57 Tbird
                2kMR2 Spyder
                62 Willys Pickup

                Wise man once told me you don’t know what you don’t know


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