Blown motor?!

[IanC]

Hey guys, I need a little help diagnosing a possible blown 10hp on my CC 100. I was mowing today and all of a sudden a loud banging sound came from the motor and it died. This motor has smoked since I got it a couple of months ago. I added some oil & MMO before I started it today.After I pushed it back into my shop, I pulled the plug and spun the motor and I felt "compression." I took the starter belt off and spun it hoping the s/g could be the culprit(couldn't be that lucky), it still made the banging sound.
Does this sound like a busted wrist pin? I'm by no means an expert on the inner workings of these motors.
What is the worst case scenario I could be facing? I'm fairly mechanical and feel I could disassemble and reassemble a motor if it needed it. What all work would I need a machine shop do(hone the cylinder, valves,...)?
I really like this tractor and feel it's worth fixing, my wife on the other hand may not be so enlightened on the matter. I gave $400 for it and would hate to have to drop way more than that into fixing it.
Thanks, Ian

[Matt G.]

Pull the head for starters. If you can still feel compression, you might have cracked the piston or something. Wrist pins don't break. Check for continuity between the piston and crank. If nothing seems amiss, I'd drain the oil, pull the motor, and take the pan off. Your problem will likely be obvious.

If you use aftermarket parts, a new piston and rod will run you less than $100. Double that (at least) for OEM. You'll also want a new governor gear, gasket set, etc. while you're in there. I don't know what machine work costs...the bore and crank on my 100 were both within spec yet... I'm going to guess $100 to $200 for machine work if you do all the disassembly/reassembly yourself.

[IanC]

Thanks Matt,
As soon as the wife gets home, I might sneak out to the shop and tear it down. I'll update what I find.
Ian

[Merk]

With the spark plug out can you see the piston go up and down?
I would remove the head to see if the valves go up and comepletely down.
Check the cylinder wall and the top of the piston for scoring on the cylinder wall and burnt piston.

Rebuilding a motor is easy to do. You need a Kohler service manual if you don't have one. The tech area in this site has a manual that you can download. When I rebuild a motor I check the cylinder wall for taper. Odds are the motor will need to be bored, crank journal may need to be undersize .010, valves will need ground or replaced depending on what they look like. Valve guides may need replaced. I would change the governor gear if it is plastic. Check the head for flatness.

I have an automotive machine shop bore the cylinder and grind the valves.

[IanC]

I pulled the head and what a mess!
The side of the piston is blown out. The debris galled the head pretty bad. There is still compression though. The valves are very crusty. The smaller of the two(sorry I don't know which is exhaust and which is intake) is so crusty that it doesn't even come close to closin all the way. The cylinder wall looks pretty good despite all that.
I'll post some pics after I get back from dinner.
Ian

[Matt G.]

The exhaust valve is the smaller one...notice that the exhaust valve is in the port on the engine that leads to the exhaust pipe, and the intake valve is in the intake port that the carb bolts onto

If you don't have an engine manual, this is a good time to download one from this site, or from Kohler's website...don't even think about trying to rebuild an engine for the first time without a manual.

[IanC]

Thanks for the tips.
Here are some pics of the carnage. I pulled the oil pan and everything underneath looked fine to my untrained eye. Like I said earlier, the cylinder looked alright to me also.
To make this even worse, I just got home from the Rocky Mtn IH Rendevous and took this 100 there. I drove it around all weekend, bragging and getting many looks and then this happens.
Will the service manuals tell me what special tools I may need?
Ian

[Matt G.]

Yep, the manual will tell you most anything you'd need to know. I'd completely disassemble everything and measure the wear in the bore and the crankpin, for starters.

[IanC]

Forgot to ask before, the head has some damage on the combustion chamber side. Can this be gound smooth, or is this head junk?
Ian

[Merk]

Do you have a good automotive machine shop near by that will do the machine work on a small motor?

You should use micrometer(s) to measure the bore and crank pin journal.