Kohler M12 Rebuild Questions


Old 08-09-06, 08:49 AM
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Join Date: Aug 2006
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Kohler M12 Rebuild Questions

This is my first rebuild...

Reason for rebuild - piston rod came apart...(into a million pieces)

I have the engine apart (crankshaft removed, piston removed).

The piston head looks to be in good shape, any reason not to continue to use it?

The crankshaft looks to have part of the rod bearing melted to it, is this crankshaft salvagable? How would one go about salvaging it?

How do you remove the crankshaft bearing from the shaft? Is this even necessary?

Thanks in advance.
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Old 08-09-06, 10:20 PM
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By piston head, you mean the top face of the piston, correct? (not cylinder head?). Just for clarification. If the piston has sustained damage or wear, it will likely be on the skirt. Often, the broken rod impacts the piston skirt and cracks or bends it somewhere. The piston also wears on the sides, at the wrist pin, and in the ring lands. Without a micrometer, you'd only be guessing as to whether it's in-spec or not. As old as it is, and from my experience with that series kohler, it wouldn't hurt to replace the piston now while you have it apart, unless it doesn't have many hours on it and is in excellent shape.

It sounds like the rod smeared onto the crankshaft. This can be fixed, assuming the crank journal underneath the smeared on aluminum is in good shape. This aluminum is often removed by soaking the crank in acid. You might just want to take the block and parts to a machine shop. Let them mic the piston, check the ring lands, cylinder, valve guides, and see what they can do with the crankshaft. They can mic it for you too, and see if it's in spec. These engines are good, and expensive if you can still find one, so it's probably worth the extra time and effort required to get it right.
Old 08-10-06, 02:43 PM
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Join Date: Apr 2004
Location: Upstate New York
Posts: 3,224
This is definitely an engine worth reconditioning. Bear in mind that if the bore is out of spec, you can get an oversized piston/rings and if the crank has sustained damage, you can get an undersized connecting rod. Machine shop service would be needed to bore and turn the crank down, if needed. You would be wise to buy a manual for this engine as it has all the specs you need to help in determining whether or not machine shop service is needed. Kohler's manual is part number TP-2203-A. Check with your local dealer for such.

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