Did I kill it?
 

So I overheated the K301 in my 125 the other day while mowing. It started to bog down and blow smoke. I shut it down and saw that it had overheated pretty bad. The gas was near boiling in the tank. So I pulled the shroud off and cleaned some grass out. While I was at it, adjusted the timing to see if that would help also. When I started it back up, it makes a horrible sort of squealing sound as I crank it. It almost impossible to start, but when it does, The squealing speeds up with the engine. Any ideas? I was thinking maybe head gasket air leak?

My guess is that you may have scored the piston. I'd take the head off and take a look at the cylinder.

Also, you may have scoured the Connecting Rod /Crank Journal....:Shocked:

This maybe a tear down and rebuild situation.

YEP!!!

You didn't "kill" it, but it's hurt... Yank it out before it gets worse and gets deeper into your bank account! Kohler cranks cost a fortune!!! (ask me how I know)!

So I pulled the head off today and this is what I found. Definitely blew the gasket but the cylinder walls look great (this is a fresh rebuild with about 50 hours on it) no signs of any scoring or abnormal wear. Now that the head is off, it doesn't make noise when I turn it over any more, which makes me thinks what I was hearing was the air leak coming through the gasket. Given what you guys see, do you still think I should tear it down? Everything sounds good internally.

Another pic of the head and gasket

If the crank assembly is able to be turned freely by hand and you don't feel any significant drag it should be fine. Just a quick question. After the new build, did you re-torque the head after the first 20 minutes of letting the engine run at different RPM's? If not, this might be why you blew a head gasket. I would clean up the carbon deposits on the valve and the head also.

make sure you retorque the head after you run it up to temp. it helps prevent that.

You might want to deck the head again. It shows where you had a blown head gasket, which may be related to the head being warped. Also it would not hurt to take a head bolt and run it into the two closest bolt holes on the block to make sure the bolt can go all the way into the hole to bottom and both holes are the same depth.

Yup, I had retorqued everything three times while breaking it in. The gasket was genuine kohler, and I had decked the head with 320 grit on a glass plate prior to installing. I used copper spray a gasket sealant for good measure also. I guess I'll just have to repeat the process and hope it takes. Maybe the heat was just to much and warped the head.