Kohler rebuild. Help!

[psychocontractorguy 12]

I'm having problems with a couple of k-motor rebuilds. I've been fighting these for a while now, so I'm looking for help from the gurus.

First is a k301. A friend of mine (a professional mechanic, the most meticulous person I know, regularly rebuilds car engines)completely rebuilt this one from the stump up. New valves, guides, .020 over piston, crank turned .010 under, quality machine work, complete carb overhaul, new governor, etc.

I reinstalled it in the tractor, and it started immediately and ran great. I ran it for about 15 minutes, got the carb adjusted, then let everyhing cool down and checked the oil. Then I mowed for about 30 minutes.....and the engine overheated, lost power, and started smoking.

The second one is a similair story. I tore down a k181, honed the cylinder (which was well within spec) put in a new piston and rings, seals, etc. Started immediately, ran great........and exactly the same thing happened. 

Clearance on valves, end play, bore size, ring gap, etc. all check out.

We both used Stens rebuild parts. I know, I know, they're not as good as Kohler, but people do use them successfully. However, if this is the problem, I'll change my ways.

The other commonality in the rebuild process was the break in oil we used. 15-40. Maybe a dumb move?

Can anyone give me suggestions about how to get these engines fixed? I'm no mechanical whiz, but there are people on YouTube rebuilding these who dont even get the internals clean. Surely, with some help, I can get one of these running!

Please help!

[slammer302 2,155]

the only thing i can think of is timing be off to make one over heat and die out that and the carb being to lean

[MalMac 1,331]

When you loose power and it's hot, when the engine is off, can you turn the engine over by hand? You should be able to easily until you hit the compression stroke. The reason I ask this is because a friend torqued the rod to tight. Also the bore job might have been to tight of tolerance. There is a number of things that could be a miss. The fact you used Stens parts could be, but highly unlikely. They are famous for out of tolerance parts right out of the box. I know lot of people who use them with no trouble. Also is the rod oriented right with in respect to the lube hole. It's for darn sure you got something wrong. 

[rmaynard 15,425]

What I am going to say is my opinion, but I know it is shared by many.

• Always select a machine shop that has experience with small engines, specifically Kohler.
• Always have a copy of the Kohler K-Series service manual and rebuild manual on hand. (available for free download on this forum).
• Always read completely how to rebuild an engine if you are going to attempt it yourself.
• Always follow Kohler's instructions in the manual.

The commonality that I see here is the "professional mechanic". I have known many professional mechanics that I would not let touch the inside of my engine. There is a big difference between a mechanic and a machinist.

When a cylinder is bored, you should always have the replacement piston and rings on hand for the machinist to check specs as the bore is being cut. Without it, he is basically just guessing at a size.

There is nothing wrong with Stens parts. Even if they are slightly out of spec, a good machinist will adjust to compensate for differences.

Kohler recommends using straight SAE 30W, SF or better oil for break-in.

[rmaynard 15,425]

Following up on the comments I made, I would take the engine to a good machine shop as I stated above. Have them spec the engine and see what the problem is. A little money spent to have things checked out is a lot cheaper than a new engine.

[JAinVA 4,619]

Everthing posted so far is spot on.Since you will have to open up the engines again start first with the crankcase and check the orientation of the oiling hole in the rod.It has to face toward the cam.If you checked ring gap on the K81 then I would supect the rod is in backwards.Thirty weight oil may be harder to come by but in an aircooled engine,never use multiweight  dinosaur juice.Luck,JAinVA

[motor12 367]

I just finished a rebuild on a K91, one of the easiest things to forget is the orientation of the rod oil hole. It must face the cam, if not there is a very good chance it will destroy the rod and crank. As a matter of fact when I tore the engine down I discovered the oil hole was not in the correct location and the rod and crank had to be replaced. The cost of a used crank and matching rod cost more than the entire engine. As for the oil I was able to find Pennzoil 30wt at Advanced Auto, it's all I use in my Kohler motors. Good luck.

[psychocontractorguy 12]

The oil hole is oriented correctly on both engines. Rod bolts were torqued to factory spec. 

Rmaynard, the guy who rebuilt the k301 builds performance honda engines. We used Kohler manuals.

I dont know about the machine shop, but the 181 was not machoned, just honed. Are the stens rings too tight for a factory bore, even when the gap is within spec?

[rmaynard 15,425]

A machinist would be able to tell you that by measuring the bore, the piston and the rings.

[psychocontractorguy 12]

A machinist would be able to tell you that by measuring the bore, the piston and the rings.

Right. A machinist with a bore micrometer, calipers, gauges, and the skill to read said tools. My friend and I have all these things, and the list of specs to compare them with. The only thing i can figure is the oil weight issue or part quality, unless someone has some other tip.

[bmsgaffer 2,043]

No one is trying to insult you or your friend, so dont take the comments personally, but obviously something is wrong and you are telling us you did everything perfectly. But I would definately tear the engine down and double check everything mentioned.

I have had three K series engines rebuilt by a local machine shop and while they werent perfect, none has the issues that you describe.


I think the oil may have contributed to the issue, 40 grade oil will be thicker at operating temps than a 30 but i didnt think it was that significant. And the multi grade is generally not recommended in warm weather for  these engines as its too thin on startup (something generally sought after in pressure lubricated engines).
 

Edited June 27, 2015 by bmsgaffer
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[psychocontractorguy 12]

Thanks, bms, I agree that something isn't right.No dispute there. 

How much did your three rebuilds cost? Did you order parts, or did the machinist do a turnkey job? Were you using Kohler parts, or aftermarket?

[rmaynard 15,425]

Please don't misunderstand my comment. I'm not disputing that you and your friend may have all the tools and the list of specifications. But if you do, and you know how to use them, then you would not be asking if the rings are too tight for the bore. If a cylinder has been bored to .020 oversize, and you have rings that are .020 over, when they are test fitted into the cylinder, you should have the proper gap, or slightly tight. Then you grind or file them to get the right gap. You only need feeler gauges to check that dimension.

I have never had a machine shop do a turnkey rebuild. I always do the disassembly and reassembly myself. A complete rebuild for me using aftermarket parts usually runs about $125 to bore and hone the cylinder, $75.00 to grind the valves and set the gaps if needed. $85 to turn a crankshaft. I buy individual rebuild parts as necessary. And as I said, I do all but the machine work myself.

 

[bmsgaffer 2,043]

As i am missing a few tools to do a full reassembly i usually give them a short block and have them "turn-key" it.

I use aftermarket stens or bbt is it? Full cost depends on engine size but my 16hp just cost a little over $400. Parts included.

[bmsgaffer 2,043]

As a side note, if i used kohler parts the cost would more than double.