Piston size?

[NIGHTOW1]

Ok dumb question, wanted to order a rebuild kit fot my K241.
pulled head and usually i see a STD or .10 ect on the piston, all I see is the letter A.
can I assume its a std piston?

[Greenstripewideframe]

Your going to have to take it to the machine shop to see what the next size is going to be. Never just replace the piston and rings without having it bored to The next size. It May look fine but I can guarantee it is egg shaped.

[J-Mech]

Yeah, I agree with Cory Keith. You need to find out what size you need before ordering any parts. Same with the rod.

[MO fabricator]

I agree that to properly rebuild an engine you need to bore it to fit an oversized piston.

With that said it is amazing how much use you can get out of a new piston and rings and maybe a wild shot at honing with a three stone hone for a drill. On a hobby machine that you plan to put 10 - 20 hours a year on you are really not hurting anything by putting a new piston and rings in if your bore is fairly decent, and you get rid of the ridge at the top.

In the grand scheme of things you aren't out more than the roughly $100 a piston kit costs and the several hours you spend putting it in. You can still have it bored out and professionally rebuilt later if you choose to. It's also a great experience so I figure I come out ahead doing it this way.

If I can choose between spending $100 on an engine and $400 on a cool attachment or 2, Or spending $500 on rebuilding an engine to like new specs that will hopefully last 40 years I know what I would choose

Just my opinion of course, but it has worked well for me so far. I would not recommend it for a mower or something you are counting on every week. ...Though I did that with a truck once... It was somewhat of a money pit...

On your original question, you should be able to tell with a regular calipers if you are oversized or not. I feel it's safer to measure than go by a code or stamped number anyway.

[NIGHTOW1]

Yea i was just wishing it would be easy lol.

[J-Mech]

I agree that to properly rebuild an engine you need to bore it to fit an oversized piston.

With that said it is amazing how much use you can get out of a new piston and rings and maybe a wild shot at honing with a three stone hone for a drill. On a hobby machine that you plan to put 10 - 20 hours a year on you are really not hurting anything by putting a new piston and rings in if your bore is fairly decent, and you get rid of the ridge at the top.

In the grand scheme of things you aren't out more than the roughly $100 a piston kit costs and the several hours you spend putting it in. You can still have it bored out and professionally rebuilt later if you choose to. It's also a great experience so I figure I come out ahead doing it this way.

If I can choose between spending $100 on an engine and $400 on a cool attachment or 2, Or spending $500 on rebuilding an engine to like new specs that will hopefully last 40 years I know what I would choose

Just my opinion of course, but it has worked well for me so far. I would not recommend it for a mower or something you are counting on every week. ...Though I did that with a truck once... It was somewhat of a money pit...

On your original question, you should be able to tell with a regular calipers if you are oversized or not. I feel it's safer to measure than go by a code or stamped number anyway.

So, I'm going to wholeheartedly disagree. Not just as a mechanic, but because I'm a mechanic, and I rebuild and sell the K series, I've seen this done all too often and it ended badly.

So, a 3 bar hone only scratches up a cylinder. By that I mean, to the naked eye, and maybe even some crude tools, the cylinder looks round. But it isn't. A 3 bar hone follows the contour and shape of what it is given. Also, the walls of the cylinder aren't all the same hardness, so it may cut more in some areas than others. It can do that because the hone flexes and bends to the shape it is given. You can put a 3 bar hone in an egg shaped hole, and you will just have a bigger egg shaped hone when you are done.

Read this write up I did several years ago:
https://www.everythingcubcadet.com/f...cylinder-hones


As far as the cost goes.... again, I rebuild the K series "professionally". I seldom if ever have $500 in the parts and machine work. Now, if I build a custom motor, the labor goes up significantly, (and sometimes the parts) but I'm talking just cost. You can do a factory fresh rebuild (all stock parts, nothing special) for around $350. (That's "stock" as in not custom. But with aftermarket parts, not Kohler. ABSOLUTELY nothing wrong with aftermarket parts if fitted correctly.) That's not a lot of money for a brand new engine. You can say that it is isn't worth the time for a machine that only gets a few hours a year..... but I assure you Keith's tractor will get more than a few hours a month. He runs them. Plus, the guys who's engines I've rebuilt AGAIN less than 10 hours after they rebuilt them because they did it just as you suggested..... yeah, they think it's worth it too. I've redone more than a few that didn't have 10 hours on them. Guys thought they could scuff the cylinder walls, and emry the crank and put it back together. The found out in short order, you can't. *IF* you have done this in the past, I'm going to say that: 1.) You got lucky. And, 2.) The engine was likely in near perfect shape to begin with and likely didn't need an overhaul anyway. Or 3.) It was all so loosey-goosey when it was done it didn't matter if anything was perfect or not.

I'm not coming down on you.... It's just I've seen it too many times before. It just doesn't consistently work out. More often than not, you end up right back where you started, only with less money and nothing to show. For the $350 in parts and machine work, just do it right. You might even be able to get by with less if you don't do "all" the work like I would. Example: All my engines get new valves. Only reason they wouldn't is if they look brand new. Not that I can't just grind the old ones and get by, but I want a motor that will run for 40 years before it needs another rebuild. I mean.... there are a lot of these engines I tear down with standard bores. That's pretty impressive given the age. So, then there's that other question..... Why not??? Why not do it right and never worry about it again? I only like to do things once. Anyway.... Like I said, not wanting to debate it. Not wanting to cut you down. Just want you to know that it is affordable to do it right, and it is worth it.

[Greenstripewideframe]

I skimped once in my first rebuild. I had it bored .020 over but I never gave it a thought to the rod journal on the crank. I used a used rod. A few hours later it had a rod knock. If I'd have only read the tolerances in the book I would have known how crucial it was. So no more skimping for this guy.

[MO fabricator]

So, I'm going to wholeheartedly disagree. Not just as a mechanic, but because I'm a mechanic, and I rebuild and sell the K series, I've seen this done all too often and it ended badly.

So, a 3 bar hone only scratches up a cylinder. By that I mean, to the naked eye, and maybe even some crude tools, the cylinder looks round. But it isn't. A 3 bar hone follows the contour and shape of what it is given. Also, the walls of the cylinder aren't all the same hardness, so it may cut more in some areas than others. It can do that because the hone flexes and bends to the shape it is given. You can put a 3 bar hone in an egg shaped hole, and you will just have a bigger egg shaped hone when you are done.

Read this write up I did several years ago:
https://www.everythingcubcadet.com/f...cylinder-hones


As far as the cost goes.... again, I rebuild the K series "professionally". I seldom if ever have $500 in the parts and machine work. Now, if I build a custom motor, the labor goes up significantly, (and sometimes the parts) but I'm talking just cost. You can do a factory fresh rebuild (all stock parts, nothing special) for around $350. (That's "stock" as in not custom. But with aftermarket parts, not Kohler. ABSOLUTELY nothing wrong with aftermarket parts if fitted correctly.) That's not a lot of money for a brand new engine. You can say that it is isn't worth the time for a machine that only gets a few hours a year..... but I assure you Keith's tractor will get more than a few hours a month. He runs them. Plus, the guys who's engines I've rebuilt AGAIN less than 10 hours after they rebuilt them because they did it just as you suggested..... yeah, they think it's worth it too. I've redone more than a few that didn't have 10 hours on them. Guys thought they could scuff the cylinder walls, and emry the crank and put it back together. The found out in short order, you can't. *IF* you have done this in the past, I'm going to say that: 1.) You got lucky. And, 2.) The engine was likely in near perfect shape to begin with and likely didn't need an overhaul anyway. Or 3.) It was all so loosey-goosey when it was done it didn't matter if anything was perfect or not.

I'm not coming down on you.... It's just I've seen it too many times before. It just doesn't consistently work out. More often than not, you end up right back where you started, only with less money and nothing to show. For the $350 in parts and machine work, just do it right. You might even be able to get by with less if you don't do "all" the work like I would. Example: All my engines get new valves. Only reason they wouldn't is if they look brand new. Not that I can't just grind the old ones and get by, but I want a motor that will run for 40 years before it needs another rebuild. I mean.... there are a lot of these engines I tear down with standard bores. That's pretty impressive given the age. So, then there's that other question..... Why not??? Why not do it right and never worry about it again? I only like to do things once. Anyway.... Like I said, not wanting to debate it. Not wanting to cut you down. Just want you to know that it is affordable to do it right, and it is worth it.

I don't believe we really disagreed there except maybe a few fine points on price. I wasn't trying to say you get a round bore, what I meant was it's amazing how well a piston will work in an out of round and tapered hole.

And I agree it's probably a fairly dumb way to go at an engine rebuild. I see bakt4kids on ebay has a k301 rebuild kit (with piston, rod AND valves) for $114.

It's probably smarter to spend the time disassembling down to a bare block and taking it to a machine shop with your oversized piston and have it bored and feel good about having given it your best shot.

So $200 should buy the rebuild kit and pay the machine shop? Unlike a lot of you guys here I'm not retired and the closest machine shop is roughly an hour away. The one I would go to almost 1.5 hours away. So till I take off work twice and make the trip twice, I would have $400 plus my time in the rebuild.

A few years back when my 129 was still pulling mower duty the rod grenaded. (Still full of oil. Not sure what went wrong). Didn't hurt the block at all. I pulled the head and decided it was worth a shot at a new piston and rod for roughly $100. No need to pull the crank or much of anything else except the oil pan. I stuck it together without even touching the valves and only missed one weeks mowing. Broke it in on the 2 weeks growth of grass. I added an hour meter and put 44 hours on it mowing the rest of that year. About then I got a ztr and the 129 hasn't seen mowing duty since. It now has 49 hours. My only input was the cost of the rebuild kit and about 3 evenings of my time, no taking off work. It worked out very well for me. And I still have a stock size bore (plus a few thousands I'm sure, but I didn't write down any measurements) So I feel certain I can still get it professionally rebuilt later on if it gives up on me.

With that said it was not the first engine I worked on, and I really enjoy working on engines so I might have a skewed perspective.

Anyway I guess I did my part for the winter entertainment now

[J-Mech]

I see bakt4kids on ebay has a k301 rebuild kit (with piston, rod AND valves) for $114.

That's who I use!

So $200 should buy the rebuild kit and pay the machine shop?

No, more like $350, as I stated before.

Unlike a lot of you guys here I'm not retired and the closest machine shop is roughly an hour away. The one I would go to almost 1.5 hours away. So till I take off work twice and make the trip twice, I would have $400 plus my time in the rebuild.

Only a few here are retired.
Finding a good machine shop is hard. I do not have my own boring bar at present. Hope to one day, to save time and make more money, lol.
My crank grinder is 45 miles west of me. My engine machine shop is 45 miles south east of me. Frustrating to have to drive in opposite directions to deliver and round things up. Good news is, I ride a GL1500 Goldwing, and I can fit two Kohler blocks in the trunk, and several crankshafts. Obviously.... not usually in the winter though.

A few years back when my 129 was still pulling mower duty the rod grenaded. (Still full of oil. Not sure what went wrong). Didn't hurt the block at all. I pulled the head and decided it was worth a shot at a new piston and rod for roughly $100. No need to pull the crank or much of anything else except the oil pan. I stuck it together without even touching the valves and only missed one weeks mowing. Broke it in on the 2 weeks growth of grass. I added an hour meter and put 44 hours on it mowing the rest of that year. About then I got a ztr and the 129 hasn't seen mowing duty since. It now has 49 hours. My only input was the cost of the rebuild kit and about 3 evenings of my time, no taking off work. It worked out very well for me. And I still have a stock size bore (plus a few thousands I'm sure, but I didn't write down any measurements) So I feel certain I can still get it professionally rebuilt later on if it gives up on me.

Rods just fail. That's why I don't suggest using one over, even if it looks good. And by that I don't just mean using a used rod.... but also machining a used rod to accept a bearing. There are bearings available for insert, and you can machine the rod to accept them. Cost is about the same as a new rod, or just a bit more.... but it's not worth it. Only with a billet rod, and only in certain engines (pulling) is it worth the hassle. Plus, a billet rod will last through several rebuilds.

I'm sure it can be rebuilt. You can bore them to .030" over, and then you can sleeve them. So, being standard bore isn't critical at all.

44 hours is enough to know it should stay together, but I don't think it will last 40 years. Maybe if you only put 5 hours a year on it, lol. I put over 100 on my 1811 this year.... and I have other tractors that I use too. Not bragging. Just sayin, lol.

[MO fabricator]

I don't expect it to last 40 years either. I'm cool with that I'm amazed at how many hours some of you can put on you tractors. Maybe If I had more attachments? And a bigger place... Anyway sorry to nightowl for putting a bunch of stuff on your thread...

[J-Mech]

I don't expect it to last 40 years either. I'm cool with that I'm amazed at how many hours some of you can put on you tractors. Maybe If I had more attachments? And a bigger place... Anyway sorry to nightowl for putting a bunch of stuff on your thread...

Nothing to be sorry about! That's how we learn (and share). Talking through problems!