My Kohler K321 14HP rebuild thread

[Eugen]

Hi all,
I'll use this thread to document my rebuild of a K321 that came out of my 224.

The story of this tractor
This guy somewhere near Niagara had this 224 on for sale or trade. He said he got the tractor from an older gentleman who just didn't finish the restoration. The paint job was somewhat rough on it, but there seemed to be quite a few new parts on the tractor. He claimed, like many others, that the tractor runs but just needed the carb adjusted - which was new too. Well, when I got it home and played with it...



http://www.vimeo.com/406420726

If that's not convincing, how about this.


http://www.vimeo.com/406707922



Couldn't do anything about it for a while, just too many other priorities, replace the roof on the house and shed, garden, plus the other tractors. Still, took the head off and there were all kind of tell tell signs. The piston said 030 hm... so this block is probably done. The head gasket looked like new but was broken; that means probably the head is warped.

Found some time to pull the engine out about 2 months ago, and went at it, little bit at a time, as I barely can scrape a few minutes for such things. So it's going to be a long story here.

Managed to disassemble the engine, was having trouble making a good measurement of the cylinder with the cheap telescoping gauges I got from amazon. Started looking for something better and managed to score a nice Mitutoyo dial bore gauge from ebay at a really good price. Wow, what a difference in being able to accurately meausure the cylinder, repeatedly! The cylinder measured pretty much everywhere 3.533 which is right on the edge of worn out for 030 over. Some folks offer 040 over kits, but the internet says it's too much over boring for the Kohler K321, you end up with an overheating engine. Not being sure what to do, I was keeping an eye on ebay for a block, and voila, one showed up. Not only that, but it was from a Case 224, and it was STD. Pulled the trigger on it, as the price was not indecent, and shipping price was really good, which is these days a killer if it comes from the US.

This one measures the worst at 3.502 inches. The wear limit is 0.003. I could use it as is, and get a few years out of it, but since it's all ready for boring, I decided it will go to our own member Sylvester Calzone of http://enginebore.com and have it bored 010 over. He will supply the rest of the rebuild kit as well.

What about the crankshaft? The old crankshaft measured closed to 0.02 under already What to do? Went back to the ebay seller that sold me the block, wondering if he has the crankshaft belonging to the block, and he did. That one measured at 1.499

Why am I complicating myself this way? Because it's the first time I rebuild an engine, and intend to keep this engine for as long as I live.

Updates will follow, hopefully soon.

[Chad]

Great start Eugen - looking forward to following this thread!

Chad

Sent from my Moto G (5) using Tapatalk

[Eugen]

Getting a scrub before going to get bored. Was full of grime.

Engine degreaser and hot water

[ssmewing]

The Kohler K-series is a great engine to learn on. It is simple and there are quality aftermarket parts, but there are also crap parts. That is probably the toughest part. But, it seems you have that sorted out already.

You should consider a governor and governor shaft bushing. They do not fail that often. But, you have to totally take the engine apart to change one and you are nearly there now.

Boring is a must in my opinion. I do not know where you measured but, the cylinder does not wear evenly. Flatheads Kohlers develop piston slap. That is where the piston is forced to rock in the bore because of it being a flathead and where the spark plug is located. This results in the piston skirt wearing 90 degrees from the piston pin and the same for the cylinder. The bottom wear of the bore is probably very different in the 90 degrees from the piston pin.

There was a recent Facebook post where a guy had a Kohler with low hours on an overhaul and the piston wore the top edges opposite of the piston pins. That can only happen in a bore that is oval shaped.

[Eugen]

Appreciate your advice Steve!

The Kohler K-series is a great engine to learn on. It is simple and there are quality aftermarket parts, but there are also crap parts. That is probably the toughest part. But, it seems you have that sorted out already.

I'd have gotten the parts from bakt4kids from ebay, but I do want to support our local Kohler parts guy, and he assures me the parts are quality.

You should consider a governor and governor shaft bushing. They do not fail that often. But, you have to totally take the engine apart to change one and you are nearly there now.

Good idea. Hard to find a source for the bushing Kohler part 235476S, but looking.

Boring is a must in my opinion. I do not know where you measured but, the cylinder does not wear evenly. Flatheads Kohlers develop piston slap. That is where the piston is forced to rock in the bore because of it being a flathead and where the spark plug is located. This results in the piston skirt wearing 90 degrees from the piston pin and the same for the cylinder. The bottom wear of the bore is probably very different in the 90 degrees from the piston pin.

There was a recent Facebook post where a guy had a Kohler with low hours on an overhaul and the piston wore the top edges opposite of the piston pins. That can only happen in a bore that is oval shaped.

Yes, boring will be done. The measurements on this block were

	X	Y
Upper	3.5021	3.5018
Middle	3.5015	3.5003
Lower	3.5018	3.5003

[Eugen]

Got the block from Mike today. He says the valve guides are within spec so no need to replace them. Phew!

There was no need for boring, he did a rigid honing married to the 010 piston that came with the kit.

For the fun of it I measured the valve guides and indeed both are somewhere between 0.312 and 0.313 inches.

That's the best I could measure with an old Oldak small whole gauge.

For the cylinder I set the micrometer to 3.510" again, I don't have gauge blocks so I go by the 3 and 4 Mitutoyo standards I got, and hope that 3.5" is also accurate.

Set the dial bore gauge to zero against the micrometer and on with the measurement.

Which looks like around 3.505 to me.

Crankshaft needs grinding too, so that's next.

[Eugen]

So, some of you may have been wondering, if the block was standard, meaning the bore size must have been 3.5" ,then going to the next size piston which is 0.010 over, should have a bore diameter of 3.510". Here's the new piston, in all its glory:

But, in my previous post I had measured the new bore size to be 3.505", not 3.510". That's a difference of 5 thousands. Did I measure it wrong, or did Mike not bore it wide enough? You've heard before that a good shop will not do a bore without a piston in hand. That's because pistons vary quite a bit, threfore the better way is to measure the piston that will be used and add to it the desired piston to cylider wall clearance, which for this engine is 7 thousands.

Let's measure this piston. The diameter of the piston should be measured perpendicular to the pin. However, there doesn't seem to be consensus as to where the measurement should be done. Mike measured it right below the oil ring. Some people measure it about 0.7" below the oil ring, or about half way between the oil ring groove and the bottom of the skirt. Note that the top of the piston diameter is smaller than the bottom.

My measurement shows 3.502" So, according to this, the bore should be 3.509"

But Mike measured it right below the oil ring groove. So, let's measure it there too. I got 3.499". Add 0.007 as piston clearance and we get a bore size of 3.506".

I suppose we can have doubts about the tool used for measurements, which in my case is a China made micrometer. I do have a some faith in it though, because it exactly measures some 3" and 4" Mitutoyo standards.

[Eugen]

Well, well, well. Manual to the rescue. It confused me that I could not find a definitive answer where to measure the piston. Then I did.

So, different pistons require different ways of measurement. The piston I got is the first one shown on this page, with note 2, saying it should be measured just below the oil ring groove. Bingo! And clearance by the manual is 0.007/0.010. Therefore, the bore is at most 1 thou tight, with clearance 0.006 instead of 0.007. I think this is not an issue of concern.

[Eugen]

I realized this morning that my posts here may be interpreted as not trusting Mike's work, but that's not at all the case. Mike is an experienced engine rebuilder and I'm a beginner trying to understand and learn. It's fun to play with the tools too.

[Eugen]

Guys, don't mind my ramblings, but one day someone may find some of this useful. It's no secret that I like technical stuff like all of you, whether it's mechanical, electrical, hydraulics, or computers. I'm really enjoying even the littlest time I can put into this first ever for me engine rebuild. One of the things I found difficult was to trust the measurement done with the cylinder bore with the telescoping gauge. Exhibit one:

So, I got a dial bore gauge, which made the measurement much more repeatable. However, I ran into a problem with that too. The dial bore gauge also needs a micrometer. Goes like this: set the micrometer to the size the bore should be. For a standard K321 this is 3.5". To be really precise you also need accurate block gauges, or at least one of that size. I happen to have a 3" gauge, and a 4" gauge. So I can check my 3-4" micrometer at 3" and at 4", but I'm not sure if it's accurate at 3.5" too, because I don't have a 3.5" gauge. The micrometer has a ratcheting thimble so when you measure something the pressure applied to the measured object when turning the thimble is consistent. That pressure if it were to be simply applied by hand would not result in consistent accurate measurements. So, setting the micrometer to 3.5" without a gauge applies no pressure to the mechanism, therefore I again doubted the measurement.

But I found a solution to make consistent measurements without a 3.5" block gauge. First set the telescoping gauge to the largest size it can go in the cylinder bore in a diagonal manner (wrt horizontal engine block face), tighten the telescoping gauge somewhat then bring the telescoping part of the gauge upwards towards horizontality and a little past it. This is pretty standard. Now tighten the telescoping gauge well and and measure it with the micrometer. Block the micrometer to that measurement. Put the dial bore gauge in between the micrometer and set the dial to zero. The dial bore gauge usually has zero and then plus and minus 5 gradations. The idea is that once set to zero on a size that you want, anything plus or minus is easy to see. Once the dial bore gauge is zeroed in between the micrometer, take it out and measure the cylinder bore. If the needle does not go to 0, your measurement with the telescoping gauge was not done right.

Using this procedure I can say with confidence that the piston to cylinder clearance is 6.5 thousands of an inch. The confidence comes from the procedure above, and from the fact that I measured the piston using the same micrometer. So even if the micrometer may not be able to measure the piston alone accurately, or the cylinder bore alone accurately, the relative measurement has to be accurate. Well, as accurate as the Mitutoyo 3" and 4" standards are, which is way more accurate than it matters on an 50 years old air cooled engine.