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Thread: Hole in Piston (OR NOT)

  1. #1
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    Hole in Piston (OR NOT) ????

    Well, Started disassembly of my spare engine. Mainly after the cylinder head as I have a broken bolt on the water pump thermostat housing and having difficulty getting it out. Anyway, As I took the cylinder head off, the cylinders in my spare engine did not look to bad. However, I noticed what appeared to be a hole in each of the pistons. Looked odd, as it was a very neatly hole like it was drilled into the piston exactly in the center. (see Photo). The hole was in each piston. Later, I looked at my 2nd spare engine which already had the cylinder head off and there were holes in those pistons. In reading a thread from someone else who was working on there 47 cj2a, his pistons had a hole in them also. So maybe it is not actually a hole, LOL. Can anyone explain what this is, Never really seen this before (I admit that I work mostly on Motorcycles, LOL)20221028_181720 resize.jpg
    Last edited by jeep_n_john; 10-28-2022 at 10:17 PM.

  2. #2
    Super Moderator bmorgil's Avatar
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    Not really a hole John. Those pistons with the centering hole are probably original equipment. The pistons were manufactured originally in a method that utilized the centering hole to cast and finish the piston. Changes in manufacturing techniques eliminated the hole.

    That cylinder and piston look pretty good. A little oil fouled but all in all, not too bad!

  3. #3
    Senior Member TJones's Avatar
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    Quote Originally Posted by bmorgil View Post
    Not really a hole John. Those pistons with the centering hole are probably original equipment. The pistons were manufactured originally in a method that utilized the centering hole to cast and finish the piston. Changes in manufacturing techniques eliminated the hole.

    That cylinder and piston look pretty good. A little oil fouled but all in all, not too bad!
    Bob is that centering hole where they put them on a lathe to cut the ring grooves or to true the pistons up??

  4. #4
    Super Moderator bmorgil's Avatar
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    Yup that's it TJ. Everything was "indexed" off the centering hole. 5 axis CNC machining has changed everything. A good machine shop can crank out pistons. Check my post just now on new pistons.

    https://willysjeepforum.kaiserwillys...-L134-amp-F134
    Last edited by bmorgil; 10-29-2022 at 08:06 AM.

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