Overhauling a K301 - how big can you go?

Mon Apr 23, 2012 9:22 am

I have a son that wants to overhaul an engine for his 4H project. I've been looking for a K161 to mount on my Troy Bilt Horse but those are few and far between (especially with the 3/4 output shaft).

I do have an "extra" K301 that arrived as part of a package deal that had supposedly been overhauled. I mounted it on a Cub cadet 125 and it immediately began to knock. I took it out and pulled it apart. It appeared to have a .030 oversized piston (not new) and possibly new rings (the reason they they claimed it was overhauled?) and the cap on the rod was loose (bolts not tighted much less torqued properly). The cylinder walls had some crosshatching but only about half. I am assuming this engine has (had) a standard crank and a cylinder thats been bored 30 over and will need to be bored again to make it right. At what point do I go up to a K321 (14HP) cylinder? Most of the rebuild kits that can be found only go as much as 30 over standard for the piston and 10 under for the rod. Will I need to order a K321 rebuild kit or is the only part that I will want from a K321 is the piston while using the rest of the parts kit from a K301?

I haven't taken this to the machine shop yet for proper measurements but I would like some input or ideas on this before I start spending money. I have no place to go with this engine once its overhauled unless I buy another cub that needs an engine so......

Re: Overhauling a K301 - how big can you go?

Mon Apr 23, 2012 10:15 am

I think your limitation will be finding a piston that will fit. I'd take it to a machine shop and let them tell you what they can do with it. I know I had trouble finding a piston for one of the engines I had apart, and ended up not finishing it.

Re: Overhauling a K301 - how big can you go?

Mon Apr 23, 2012 8:00 pm

.030 over is the biggest you can go. Some will say you can put a K321 standard piston in. The cylinder wall could be too thin and split while running.

I had two K 321 blocks sleeved several years ago. Both are back to the standard bore. Cost including the sleeve and installation was around $90 each.

Re: Overhauling a K301 - how big can you go?

Mon Apr 23, 2012 9:16 pm

My son Aron belongs to a 4H Club - Piston Pushers - working on small engine equipment, etc. His K241 needed a rebuild so he brought the bare block to a machine shop that the club advisor has worked out a deal with. No charge to bore the cylinder for engines belonging to 4H youth active in the club.
Check with the club advisor and see if they have made similar arrangements.
Our kids also get a discount at several outdoor power equipment dealers in the area on parts.


Re: Overhauling a K301 - how big can you go?

Thu Apr 26, 2012 3:34 pm

One of the adult members of the 4H club may have the equipment necessary to measure the engine bore. Another thought is to invite a small engine mechanic to a meeting to demonstrate how to measure the important parts of a small engine.

A standard set of calipers with a dial or digital reading will provide enough information on the bore to tell if it's usable. They sell an inside (bore) reading calipers set - fairly expensive.

If the Kohler doesn't pan out, there are tons of Briggs & Stratton engined push lawn mowers out there. You could obtain a "junk" lawn mower for next to nothing. You can usually get a B&S lawn mower engine into running condition quite inexpensively.

Re: Overhauling a K301 - how big can you go?

Fri Apr 27, 2012 10:53 am

Given the specifications of boring and turning a crank those duties will be left to the machine shop. The engines I've overhauled in the past usually run about $40-$50 for all the machine shop work - including grinding the valves and seats - if needed or possible. Basically my son will be learning to tear down then assemble the engine with a health emphasis on the importance of proper torque on specific bolts.

He’s only 9 so I hope his interest in these types of projects grows with him. In 5 or 6 years I’d love to have him overhaul the 351W in my Bronco.

Weren't some of the older K301s build with thicker walled blocks that made turning them into K321s no big deal? Or am I remembering things that didn't happen?

Re: Overhauling a K301 - how big can you go?

Sun Apr 29, 2012 7:21 pm

Worth reading the entire article.

NOTE: Some 10hp Kohler engine blocks have K301 embossed in the casting on the PTO end. These blocks have a thicker cylinder wall and can be safely bored for a 12hp piston (even up to .030" oversize), without making the cylinder wall too thin. They cannot be bored for a 14hp piston though.

The K301 blocks with a 10hp bore can be safely bored for use with a 12hp piston. The K301 blocks are actually a 12hp block with a 10hp bore. There's nothing special about this blocks, except for the thicker cylinder wall. They weren't used in any "heavy duty" specific purpose either. What happened is on the production line at Kohler, when they ran out of 10hp blocks, they grabbed a bunch of 12hp blocks and bored them for use with a 10hp piston to finish the production of a bunch of 10hp engines. And not all Kohler blocks that have the K301 characters are actually 10hp blocks. Some are bored for a 12hp piston assembly (3.375" STD bore) and therefore, are a 12hp block. The ones that are bored for a 10hp piston assembly (3.250" STD bore) have a thicker cylinder wall and therefore, are a 10hp block. To determine which block is which, the diameter of the cylinder bore needs to be accurately measured.

Re: Overhauling a K301 - how big can you go?

Mon Apr 30, 2012 8:57 am

Looks like I was mistaking the charactoristics of the 10hp engine for the 12hp engine.

Re: Overhauling a K301 - how big can you go?

Mon May 21, 2012 3:57 pm

I had a customers gravely tractor that had a 12hp kohler that as at the .030 limit and needed to be refreshed. The bore if i remember correctly was at .032" rather than .030'. It was a few thousands past the bore limit after i cleaned up the bore with the gear driven hyone that trues the bore top to bottom and makes it round. I installed a new .030" piston and rings off setting the ring gaps 180 degrees from each other and assembled it. She ran great. The owner didn't have the $$ for a new block at the time but he was a great customer in the past. I took a chance and got by with it.

Re: Overhauling a K301 - how big can you go?

Tue May 29, 2012 2:13 pm

I have the gear driven hones, one hone goes up to 3'' and the other goes from 2.75'' and up to 10'' with the larger racks. I have used this type of gear driven hone before. I also have roughing stones, medium grit stones and fine grit stones for both hones too. This way i can bore the cyliner to exactly what i want and hold it round and keep the taper of the cylinder down too.

Re: Overhauling a K301 - how big can you go?

Fri Jul 13, 2012 1:51 pm

I been putting my extra mad money into new pistons and rings and i been purchasing used engine blocks on ebay to have them inhouse.

Re: Overhauling a K301 - how big can you go?

Wed Jul 25, 2012 3:01 pm

Here's the kohler engine specs. www.yetmans.mb.ca/kohler/page4_5/page4_5.html

Re: Overhauling a K301 - how big can you go?

Mon Jul 30, 2012 9:25 am

Back to my son's project.

Turns out the cylinder was .020 over bored but was round. The machine shop honed the cylinder and said it was fine. The problem was the crank. It had a fairly new (new?) rod that was .020 under sized but the crank journal was .020 to .025 undersized. I had the shop turn the crank .030 undersized and sent the rod off to A-1 Miller's Performance in Missouri to get their Federal Mogul bearing insert that they use to go .030 undersized. That was in early June, they cashed my check and I've called 4-5 times asking where my rod is. I get the same old line - we're behind and it should be out this weekend. 4H fair starts Thursday - since it didn't arrive over the weekend (like promised again) most likely this engine won't be making the trip.