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jeep_n_john
10-28-2022, 10:08 PM
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)9935
bmorgil
10-29-2022, 06:28 AM
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!
TJones
10-29-2022, 07:37 AM
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??
bmorgil
10-29-2022, 08:03 AM
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.com/showthread.php?3111-A-New-Piston-Choice-for-the-L134-amp-F134