K301A vs K301AS & 'rebuild kits'
 

My 125 has a K301A on it that is quite tired. It runs pretty good, but I'm pretty sure I hear a lower end knock and it seems like it burns almost as much oil as it does gas, and considering its age and the fact that I'm pretty sure it's the untouched original engine, I'm pretty sure the cylinder bore is 'not exactly round' at this point.

I have a K301AS that my Grandfather also had, and while know that the 'A' denotes a shallow oil pan, my google searches haven't given me much on the 'AS' (everything pretty much comes back to the 'A'). I assume that means shallow oil pan and something else. What's the difference between the K301A and the K301AS?

First, is there any reason the K301AS couldn't be rebuilt and dropped into the 125, and assuming there is no issue there, what are my options for pistons to rebuild it? I'm sure I'm going to need a larger piston of some sort as it's most likely going to need some material removed to make it round and square again. I would imagine there are a few 'stock' oversize piston options intended for rebuilds. Or might it be possible to bore it out for a stock K321 piston, which would (almost) certainly true up the bore)? J-Mech, do you sell any 'rebuild kits'?

Any other suggestions for rebuilding this?

Well, lets start with the first real question. What does that "S" mean. If you open up your Kohler K series service manual, on page 1.3 you will find a description for each of the characters in the model. The "S" means electric start. Not starter/generator. Electric start, like a QL tractor. So.... will the K301AS work in your 125..... not as it sits. Can you take both engines apart and use the external parts off the 125 engine, yes you can. You will need the rear bearing cover, flywheel and all the engine tins. Basically, you would just use the block and internals.

Can a K301 be bored to a K321. NO IT CANNOT.

You don't ever rebuild a motor without boring it, and grinding the crankshaft. Said this at least 1000 times on here. Plan on it. Do it. Don't consider doing less than this. Plan on grinding the valve seats, and putting new valves in too. Might need valve guides. Plane the head. As of recent, I've been decking all the blocks too. Seems like so many I'm tearing down now have that same low spot up by the exhaust valve. Same area the head is always low, and it blows head gaskets in that spot first.

Yes, oversize/undersize pistons and rods are readily available. Easy to get, and easy to find. I use this guy: http://www.ebaystores.com/The-Mans-O...=p4634.c0.m322 I already linked you to his page with Kohler parts. Now and again, if I need something he doesn't carry, I buy from isavetractors.com. Sometimes I check price between the two, but usually they are really close. If you order from the guy on ebay, shipping is usually free.

As far an any other suggestions for rebuilding this.... YES. I have a K301 ready to assemble that I was waiting on someone to need so I can set it up for whatever "code" they needed. PM me if you are interested.

Boring the block was never a question - it was foregone conclusion. The only question was (and is) how much. I had asked about boring it out to a K321's bore because I had read a blurb somewhere about someone apparently doing it - I'm guessing it's one of those things where it 'technically' can be done, but it's not a good idea for one reason or another. Either way, since you said no, I'll plan on boring it the least amount possible to get the proper clearances for whatever piston size is required (To be honest, if you had said 'yes, that can be done without issue', then I probably would have gone that route - 2 extra HP plus just order the parts hand have it machined to properly clear that piston and it's done vs having to first determine how much material needs to be removed to true it up before I can order the parts). If it can be trued up and properly clearanced for a .010 over piston, then that'll be it. Same goes for the crank - there is some rod material on the crank, but not a whole lot, so hopefully a .010 under sized crank will do the trick.

Thanks for the tip on decking it.

And thanks for the offer on the engine you have - I want to try my hand at a full rebuild on this one. WAAAAY back in high school, in one of my classes, we took apart and 'rebuilt' lawnmower engines at one point. Mine ran and didn't blow up lol. Since then, I've done a lot of automotive motor work - engine swaps, head gaskets, etc on v6's, v8's, gas, diesel, pushrod, OHC, DOHC, etc - just never a full rebuild including the rotating assembly (and there are several people that won't let anyone but me touch their vehicles as I've put new life into their vehicles a few times FWLIW). Pretty much all top end work. Now, if I get this rebuilt and it goes horribly south, then I'll come see you about rebuilding the other block.

Next time I'm out at my grandmothers, I'll have to see if there are any more CC engine parts laying around - I know there's another motor that my grandfather had taken apart, but I don't recall what model it was. If I can get the parts to rebuild the K301AS as a K301A without having to first take apart the existing K301A, that would be ideal. In a perfect world, I'd like to get the engine I have apart fully rebuilt and ready to do a straight swap in one swoop.

No, not really. Oh, there's a lot of "technicality" about it.... the cylinders aren't thick enough. Not to hold very long anyway. Not saying someone didn't do it, I'm saying don't because if you do get lucky and have a cast that is thick enough, it won't last long. Not all engines are cast the same. Some are thicker than others. Only blocks that can be bored bigger with certainty are the K161's which can be bored to the larger 2 15/16's bore if they are the 2 7/8's bore. SOME of the K241 blocks can be bored to the K301 size, but not all of them. Outside of that, not a good idea to go much bigger than the standard oversizes unless you like boring into cooling fins, or paper thin cylinder walls.... or cylinders that look good, but sheer off the top of the block at the base of the jug after some hours of run time and load.


Better read the book real good. Air cooled motors aren't car engines.

Jon- I thought you were using bakt4kids for parts

That is him. His store is called “the mans one stop shop”

I am..... that's who I linked to. Store name is "The Man's One Stop Shop" maintained by ebay seller bakt4kids. :beerchug:

Edit: Mike beat me

https://www.onlycubcadets.net/forum/...ad.php?t=54042
(Please read my above thread about "smoking K301 after rebuild")
Bought that kit from him, last correspondence from him was questioning my abilities for rebuilding a motor. Given the right instructions the first time would have produced a non smoking motor. Never again!!