Back in the 1979, I was mowing a field for a party and threw a rod.  I had it rebuilt and my father used it for the next 35 years or so.  Fast forward, the motor was tired to say the least and my wife had just started to mow.  I have always listened to my machines when I operate them so I immediately heard a scratching noise and ran over to where she was and shut it down.  It was low on oil, not out of oil, but I filled it up and turned the motor over with the starter and the plug wire pulled so it would not start just to get it lubed again with oil.  I have used the tractor just above idle to pull the cart doing odd jobs and it ran fine, no noises, but I decided to tear it down as I knew there had to be issues.

So on tear down, this is what the condition of the motor.

The bore is fine, no scoring, the piston is fine, no scoring.

The rod bearing surface had a bit of scoring, but the crankshaft rod journal still measures standard and has no scoring.

The counter balance gears look good, the teeth are not damaged, but there is more than acceptable play in the bearings.

The valves I look good and I could not detect any side play so the guides appear to be ok.

The crankshaft has no detectable end play.

There were no shavings, chunks, etc. in the oil pan.

I plan to rebuild the motor with a new piston, pin, rod, gaskets, valves, counter-balance bearings (and new shafts if they are worn), points.

Is there anything any of you can think of that I should or should not do regarding my rebuild?  I've rebuilt a WD45 motor so I do have some experience but I would certainly appreciate any pointers from more experienced rebuilders.  The fact the rod journal was not damaged leads me to believe I was lucky in that the motor had just been started and had not been allowed to get hot and run hot really tearing things up, so I plan to check the crankshaft ball bearings but probably not replace them unless bad.

I'll post pics and updates as I go along and any help will be appreciated.

The Kohler K-singles take well to a basic rebuild.  As Mike noted, you WILL find taper and out-of-round, which is very normal for basically ANY flathead, as the thermal expansion of the block is NOT consistent by virtue of all the asymmetrical iron on one side, and the airflow which comes along with cool intake alongside warmer exhaust... just nature of the beast of ANY flathead, and more prevalent on air-cooled motors for obvious equalization reasons.

That being said, when you warm the block to operating temp, lots of the taper and out-of-round go away.

You noted more-than-acceptable play in the balance gears.  MOST guys that rebuild with the intention of keeping the motor alive, remove the balance shaft assemblies altogether, simply because the largest number of catastrophic failures for these engines, is balance-gears dismantling themselves at speed.  The last three 301's I went through, got the 'grenade gears' removed, and have not given me any trouble doing so.  The balance gears' function is to reduce the primary imbalance inherent into any single-cyl, but the balancing arrangement was not part of the original design, and it's suppression isn't really significant in the application of a garden tractor.  The engine certainly won't 'fail' as a result of the balance shafts being deleted.

The main bearings are robust.  The stock rods are very strong on these, but every once in a while you'll get reports of rods breaking, in every case I've investigated, the broken rod was accompanied by the presence of a brand-new, undamaged connecting-rod nut sitting in the bottom of the pan... meaning, the rod failed because the cap became unsecured.

In more than one of the K-singles, a failed rod didn't go through the block... but the big end DID manage to chip a little off the lower end of the cylinder.  When this happens, take a die grinder and a stone, and soften the edge of the broken area, rinse it good, and proceed with any block machining, then reassemble with new parts and go.  The motor in my Cub Cadet 109 is this way, and has NO issues whatsoever.

The nice thing about these K-series, is that really good aftermarket parts are very inexpensive... last half-dozen or so I did, I used rods, pistons, and rings from STENS.

Clean up those valve guides... I have a little spring-blade reamer that I run through, then lap the valves in.  True the head flat and clean for a good seal. make certain the ACR mechanism (on the exhaust valve lobe of the camshaft) is working properly, and you'll have a good-running motor.

Note-

When you rebuild a K-single, don't be shy about break-in.  Get it started, get timing and mixture set, then take it out to the road, put it in high gear, and make it pull the hill a good minute or two, then let it cool as you go back down, then pull again... give it three good pulls at least, so the rings bed in properly.  These engines really need to be loaded to get the rings to seat... if you don't, they're not gonna seal.

 Something that produces power from an outside source, electricity, is a MOTOR.

That's why we have steam engines, air motors, outboard motors, database engines, and motor cycles, rocket motors and seige engines.  Then there's cotton gins (short for enGine)  if you're driving a car, you're a motorist on a motorway, and if you're operating a electric locomotive, regardless of wether it's powered via catenary wire, 3rd rail shoe, fossil-fuel turbine, or compression-ignition internal combustion, you're an Engineer.  Then there's the Stirling Engine, both tracton motors and traction engines, Ericcson Cycle solid-state engines, reaction engines, and logic engines, intertial motors, servo motors, and economic engines.

Neither engines nor motors PRODUCE power.  They simply CONVERT some form of potential energy, into to some form of kinetic.  How the term Engine and Motor are used within language is irrelevant, because the attempt at enforcing a linguistic disposition has no effect on how any of them actually work, and it is entirely irrelevant to the content of this thread.

Every language has it's share of voids.  In French, there's a word one uses to identify appreciation for something... that is Aimer.... as in J'aime  (I love).  In American English, we use the word 'Like' to appreciate something, and the word 'Love' to appreciate something substantially more... however, in French, there is not this same parallel- you either love something, or you do not.  Since our word "Like" is a comparision operator that identifies similarity (red is 'like' orange, and a pencil is 'like' a pen), there is a gap in translation.

Note that neither the words Engine nor Motor come from American English.  If they're not used to your liking, you're welcome to exprimez-vous dans la langue que vous preferez.

HudCo wrote: i thought that the 12 horse did not have balance gears but all the ones bigger k14 hp. and up.   i never could get any kohler expert tell me if you could leave the balance gears out but i have had to learn that the hard way over the years that if part of the balance gears system including the shafts it will blow up but no one wants to spend that much money

Yeah, we refer to them as 'Grenade Gears' for good reason.  Generally speaking, the fitment when new wasn't a serious problem, but years of hard work trying to keep the heavy thumper docile results in wear of those shafts and gears, and eventually enough gear lash shows up that the reactions between shafts and crank become enough to hammer them to pieces, and that's when very bad things start to happen... but I'm happy to report that none of the K301 or K321's I've been through have let go after having the balancing arrangements deleted.  Also note that the K241 in my 109 (which didn't have balance shafts, but DOES have the lower cylinder wall edge missing a mouthful) is extremely happy to pull hard at 4200rpm, even though the flywheel isn't steel.  I would not recommend anyone else do it, and I don't do it often, but when I let it roar, the '10hp' advertised output goes right out the window.

I did have a plan on the drawing board for a salt-flats machine... by reversing the transmission gearing, tall skinny, bald tires on independant suspension with disk brakes, shortening the K241's stroke, adding boost, and going with steel flywheel, crank, forged rod and piston, winding it up to insanity...   then I just built my little Cub Cadet 'Loader-Mutt'... which under equal, but different insanity, is in process of getting an Auburn limited-slip differential and Dana 60 Full Floater axles...

  Have 3 New Holland tractors S16 - (Ariens now) one with Vickers Hydrostat other 2 with Sundstrand units in rear , Just bought another Ariens for $300 with mower , 2 stage snow blower, wheel weights and chains - but whoever worked on it last used silicone  for block to pan joint and gasket slipped out so it spews oil from gasket sliding out from block .

Coke, You seem to have a problem with keeping oil in the crankcase... LOL! Don't ya hate when people use RTV for a pan gasket? Not only does it blow out, it also gets in the engine as well and gets slung around messin' things up. Ugh!  I picked up a Briggs engine  and after getting it pressure washed off noticed all the Blue goo hangin' out the sides of the oil pan. Popped it apart and everything was full of Blue goo. It's a wonder the engine didn't smoke or blow. It was everywhere. Ran good after I got the crankcase spotless again. What a job that was.......

Steve@B&B

Are the balance gears a problem in just the Kohlers or do the B/S engines have the same problem? I just went through the 14HP Briggs that's in my 3314V. Everything looked pretty clean and not to worn inside, but should I remove those balance gears whilst' the engine is still sitting on the work bench? I plan on using the Tractor for plowing snow....

Steve@B&B