Head removed from my Kohler 12 horse

[troutbum70 858]

Removed the head from the Kohler 12 horse yesterday, I am no expert with these. So looking for thoughts on what I found.

[bc.gold 3,406]

48 minutes ago, troutbum63 said:

Removed the head from the Kohler 12 horse yesterday, I am no expert with these. So looking for thoughts on what I found.

 

Judging from the carbon footprint would venture a guess the valve guides are needed to be replaced. The larger valve is intake, air and fuel mixture - incoming mixture keeps oil vapours cool enough their not instantly turned into carbon.

 

If the piston rings were worn then oil would enter the combustion chamber on every downward stroke, on the power stroke when the cylinder gas's are at their extreme temperatures the oil being burnt would fully carbonize the entire piston top. Especially noticeable around the entire circumference of the piston.

 

Check your valve guides for wear and make sure the PCV ( positive crankcase ventilation ) valve is working properly.

Edited May 15, 2020 by bcgold

[squonk 43,837]

Clean the gunk on the edge of the piston nearest the exhaust valve and look closely. I just took a 16 HP apart and the piston edge had barely started to melt 

[Pollack Pete 2,273]

How was it running prior to the head being removed? Burning oil?Reason for removing head??

[bc.gold 3,406]

23 minutes ago, squonk said:

just took a 16 HP apart and the piston edge had barely started to melt 

 

Engine running lean  fuel mixture, cracked piston would be from detonation.

[troutbum70 858]

Sounded ok sitting but lacked for power when going up hill, done a leak down test and intake valve had a very noticeable leak. Done valve adjustment as both were tight, but did not help valve leak. Carb also needs serious attention, throttle shaft is pretty loose. When engine was running the carbon monoxide being given off was horrendous. Don't know much history on this tractor as I just purchased it back in the early February, and previous owner could not tell me much. He had had it a couple years but did not use it much, maybe these things are why hi hi.

[pfrederi 18,681]

25 minutes ago, troutbum63 said:

Sounded ok sitting but lacked for power when going up hill, done a leak down test and intake valve had a very noticeable leak. Done valve adjustment as both were tight, but did not help valve leak. Carb also needs serious attention, throttle shaft is pretty loose. When engine was running the carbon monoxide being given off was horrendous. Don't know much history on this tractor as I just purchased it back in the early February, and previous owner could not tell me much. He had had it a couple years but did not use it much, maybe these things are why hi hi.

 

 

Carbon Monoxide is odorless.  was it oil burning smell rich gassy smell???

[troutbum70 858]

No did not smell like burnt oil, never saw any smoke coming out of it. What I have ran it it has not used any oil. I work in my basement so did not dare to start it/run in there, wife would always have terrible fit because of the smell.

[Stormin 9,985]

Definitely needs a decoke and valve grind. If it wasn't burning oil, then rings and bore sound ok. What is the head gasket like? Top looks ok but what is the bottom like?

[prondzy 3,889]

8 hours ago, troutbum63 said:

Removed the head from the Kohler 12 horse yesterday, I am no expert with these. So looking for thoughts on what I found.

You have an oil burner that's due for a complete rebuild/oversize piston. The clean "C" shape on the piston is from oil getting by the rings and resting there while not running.  The white exhaust valve is also an indicator of burnt oil.  I vote a rebuild if its going to be a worker,  but it will still hold on for quite a while if only used for light work.  Clean the carbon and install a new head gasket.

[troutbum70 858]

Started to clean up top of piston, found a small hole right in the center of the piston. Does not go clear through piston, I am guessing it does not belong there. Included couple pictures of the head gasket. Is there a way to tell if it is the original piston? 

[tunahead72 2,546]

25 minutes ago, troutbum63 said:

... Is there a way to tell if it is the original piston? ...

 

Keep cleaning the top of the piston.  If it's a Kohler piston, you should eventually see a pretty clear marking there, either STD for standard, or a number indicating how much over the standard size it is, like .020".

 

I have no idea what the hole means, it looks too perfectly round and centered to be an accident or a result of some kind of damage.  I'd say it was deliberate, but I don't know why.

 

[troutbum70 858]

That's what I was thinking should be some kind of stamp in top of piston, I would think if the hole was made from carbon build up on head it would not be so perfectly  centered and round. Almost like it was drilled, it is not very deep.

[oliver2-44 10,727]

I’ve had pistons with a center hole like that. It looked like a tapered hope that a lathe center would go in when machining the piston at the factory

[troutbum70 858]

Okay so maybe the hole will cause no problem, was hoping to not do a complete tear down. Maybe have valves ground, clean valve seats and put back together. MAYBE