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..replacing rod and piston ....

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My first post. Will be installing new piston, rings, and conn rod on an AC 712H(piston fractured). While I have a fair amount of technical background, is there anything specific I should keep in mind while doing this replacement in the 12HP Kohler?

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arjr111
Hi Bob, just replaced the Rod, Piston, and Rings in my K321. Fairly, straightforward job. Some of the pistons (depending on the style piston you buy) need to be facing the right way, mine went in any direction. And the oil hole on the rod, needs to be facing the cam. The K manual gives a nice description of the job. If you have the ring expander, ring compresser, and the ridge reamer (I did not even need the reamer), torque wrench, in both ft and inch lbs. (the rod bolts are inch lb) you should encounter no problems. I also, roughed the cylinder walls with one of the inexpensive honers available from Foley-Belsaw.....Art

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acjohn
Bob, I just completely rebuilt my K241 (10 HP). IMHO it is a waste of money to install new rod, piston and rings without measuring the bore to be sure it is round and to size. If it is worn, it will be oversized in the thrust direction (toward and away from valves). Be sure you go by the book on the piston clearance on the thrust side. Yetman's says .007/.010 clearance on the thrust face. If your bore is oval shaped, you will need to bore and hone to true it up. I had the advantage of doing both myself, so I don't know what a machine shop would charge. I had to go .030 over since the bore was worn .020 over in the thrust direction. I also milled .030 off the head to boost compression. Still runs pump gas and probably pushes close to 13 HP now. Good luck. It is a simple engine and will last a long, long time if you change oil regularly.

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acjohn
Bob, almost forgot, the rod journal diameter should be no more than .0005 out of round. Mine was .0015 so I polished the sides with emery paper (took about 1 hour) but got it within .0003 of round. You will need to size the rod to the crank because the crank will likely be worn. Be careful not to remove too much material as it will knock. Kohler posi-tork rod bolts cannot be retorqued. Do not use plastigage for this reason. Mic the rod and crank until you have the specified clearance. Yetman's (on this site) has all the data for your engine.

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MATTHEW
Hi Bob. I own an automotive machine shop here in Arizona. The only thing that hasn't been mentioned is when you are done honing the cylinder, or when you get it back from a machine shop is to wash the entire block, cylinder included with hot soapy water. use liquid detergent. This procedure will remove all the microscopic pieces between the hone marks in the cylinder. After washing use some oil immediately on the cylinder to keep from rusting. Matt

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