Blown head gasket,

[Doc Watts 9]

While mow today , my C120 started running rough. I shut it down only to notice oil leaking from the head gasket area. What should my first move be ?  This is my first post . Thanks for having me. 

[oliver2-44 10,367]

You will need to pull the head. But start by spraying all the bolts on the head with your favorite penetrating oil  Especially the ones by the exhaust and the little one that bolts the tin to the side of the head. Do this a couple of times a day for a couple of days.  
Clean the area around the head so nothing can get into the cylinder. 

When you start removing bolts loosen slightly, spray penetrant, tighten a little, then loosen. Repeat this until the bolt is turning freely.  Don’t force them, a broken bolt is even a bigger problem. If the bolts by the exhaust down want to move, keep soaking with penetrant and let us know so we can help. 
Most of the time they come out without a problem. 
I like to Buy a head gasket that has a “Ring”  right around around  the cylinder. To me these just seem a little better. 
You should sand the aluminum head flat. There’s a simple procedure on here one of us will post for you. 
Pist a picture of the bottom of the head, the old head gasket and the top of the engine wit the piston at the top. 
While the head is off it’s an ideal time to clean any carbon off the head, piston and valves. Use a plastic or hardwood scraper so you don’t scratch the aluminum piston. 
To reinstall you will need a torque wrench. If you don’t have on most auto parts stirs will loan you one. 
Go to the manuals section and down load the Manual for you engine if you don’t already have one. 
There will be a procedure/sequence to tighten the head bolts with the torque wrench. 
Sanding the head flat and properly torquing it should cure the problem. 
Per the manual you should run the engine to warm it up good, then retorque the head bolts. 

[ebinmaine 70,725]

4 hours ago, oliver2-44 said:

Clean the area around the head so nothing can get into the cylinder. 

When you start removing bolts loosen slightly, spray penetrant, tighten a little, then loosen. Repeat this until the bolt is turning freely

 

Excellent description and Worth reading again so I quoted it.  

 

4 hours ago, oliver2-44 said:

You should sand the aluminum head flat. There’s a simple procedure on here one of us will post for you. 

 

IMHO: planing the cylinder head  IS NECESSARY. 

 

 

 

Here's a video of my Other Half, Trina showing how we use a FLAT CLEAN piece of steel with sandpaper taped to it to plane our cylinder heads.

 

 

 

 

 

I don't rotate them as fast or often as she does but it's a personal preference.  

It'll need to be rotated maybe every 10 to 20 strokes.  

 

We normally start with 180 grit. 

Got to 240 or up to 320 ish. 

Finish off with 400. 

 

 It takes varying time to complete depending on how warped the head is. 

 

5 hours ago, Doc Watts said:

first post

 

[ri702bill 8,968]

Welcome! Once it is disassembled, chase the head bolt threads in the block to allow getting good torque readings upon assembly. Use a good sharp tap BY HAND, don't be a hero and chuck it up in a cordless drill. Extracting a broken tap is not my idea of a fun time. Do look up the recommended head torque sequence in the manual - it defines not only the pattern, but the progressive steps - you cannot go for full torque in one pass...... 

Retorquing the head after it has been run and cooled down is super important - had to retorque a 6 HP Tecumseh thru SIX thermal cycles to achieve a proper torque reading when cold.

The head gasket compresses to seal - if you are able to get one with the afore mentioned "Fire Ring", that has to crush down a bit.... and fights you as you go.

While the head is off - inspect the valves and seats for visible damage. Roll the motor over by hand to allow each valve to open - the exhaust is usually the one that takes a beating over time...

 

Edited June 20, 2023 by ri702bill

[Achto 28,777]

 

Looks like the guys have you covered.

[Pullstart 64,531]

[Sailman 1,299]

Bought a C-120 once that the PO stated something was wrong with the engine, possibly a rod going. It would run but made an awful noise. I noticed a black spot along the head where the gasket appeared to be leaking. Followed the directions from folks on this site as listed above. Planing the head is critical. The thing now starts and runs smooth as silk!

Suggest you adjust the valves and check the points while you are in there, as well as de-carbon.

 

[oliver2-44 10,367]

1 hour ago, Sailman said:

 

Suggest you adjust the valves and check the points while you are in there, as well as de-carbon.

 

Excellent suggestion.

We can help you if needed. The Kohler manual has details on this.

 

7 hours ago, ri702bill said:

Welcome! Once it is disassembled, chase the head bolt threads in the block to allow getting good torque readings upon assembly. Use a good sharp tap BY HAND, don't be a hero and chuck it up in a cordless drill. Extracting a broken tap is not my idea of a fun time. Do look up the recommended head torque sequence in the manual - it defines not only the pattern, but the progressive steps - you cannot go for full torque in one pass...... 

Retorquing the head after it has been run and cooled down is super important - had to retorque a 6 HP Tecumseh thru SIX thermal cycles to achieve a proper torque reading when cold.

The head gasket compresses to seal - if you are able to get one with the afore mentioned "Fire Ring", that has to crush down a bit.... and fights you as you go.

While the head is off - inspect the valves and seats for visible damage. Roll the motor over by hand to allow each valve to open - the exhaust is usually the one that takes a beating over time...

 

Excellent

[ineedanother 1,394]

12 hours ago, ri702bill said:

 don't be a hero and chuck it up in a cordless drill.

[ineedanother 1,394]

6 hours ago, Sailman said:

Suggest you adjust the valves and check the points while you are in there, as well as de-carbon.

Valve adjustment might be intimidating until you do it once and see how simple it is. You will need to pull the carb to pull that cover though. I check the clearance before I de-carbon just to see the difference a carbon buildup makes. You'll likely need that set of valve cover gaskets but they're cheap. Get them when you order the head gasket so you can combine the shipping. 

[ri702bill 8,968]

39 minutes ago, ineedanother said:

Valve adjustment might be intimidating until you do it once and see how simple it is. You will need to pull the carb to pull that cover though. I check the clearance before I de-carbon just to see the difference a carbon buildup makes. You'll likely need that set of valve cover gaskets but they're cheap. Get them when you order the head gasket so you can combine the shipping. 

All good advise... IF you find you need to "Adjust" the valve clearances ( I am assuming the larger 12 HP engine adjusts the same as an 8 HP), you will need to remove the valves. Too tight, the stems can be ground, too loose means a new valve....

If you are in that situation, might as well yank the motor, remove the oil pan, and clean it out. Not something you do on a regular basis. Then order a complete gasket set...

[ebinmaine 70,725]

44 minutes ago, ri702bill said:

Adjust" the valve clearances ( I am assuming the larger 12 HP engine adjusts the same as an 8 HP), you will need to remove the valves. Too tight, the stems can be ground, too loose means a new valve....

No no sir. 

 

Big block Kohlers have screw turn adjustable valves.  

No replacement necessary.  

 

 

[Sailman 1,299]

All you need is a feeler gauge and 2 wrenches. Adjusts just like an old Harley engine....

7/16 wrench I think, but not for sure. 1 to hold the nut in place and 1 to turn to adjusting screw.

You do need to remove the carburetor, and replace the gaskets on the cover. Make sure you pay attention to the order of parts under the cover and orientation of the reed valve. Really an easy job to do. Tappet clearance (per kohler manual) on the K301 (12 hp) is .008 -.010 on the intake and .017 - .019 on the exhaust. Be sure to adjust cold. 

Section 3 in the attached manual walks you through everything mentioned in this thread.

Kohler_Engines_Service_manual.pdf

[Doc Watts 9]

Thank you all for your suggestions. I’m going to take my time at this . I don’t want to make a mess out of the situation. This C120 sat in the woods for 15 years at  a hunting camp. I rewired it changed the fluids cleaned it up and and it ran like a dream . Been using it for a year. Thanks again. I’ll let you all know.

[oliver2-44 10,367]

If you are going to do the valve adjustment you might check eBay or Amazon for a complete gasket set.  It might be less costly than ordering individual gaskets if you haven’t ordered them yet. 

[Wild Bill 633 866]

I would also suggest new cylinder head bolts.

[Jon Paulsen 291]

...and maybe a bottoming tap to chase the threads... especially if they bolt come out nasty. After 15 years of rain and winter weather, those head bolts may be their own project. Go slow brother. 

[ebinmaine 70,725]

26 minutes ago, Wild Bill 633 said:

I would also suggest new cylinder head bolts.

Excellent suggestion.

 

 

11 minutes ago, Jon Paulsen said:

those head bolts may be their own project

Quite true. .

 

ALWAYS TIGHTEN  just a tiny bit first. 

Then LOOSEN it the same amount.

Repeat this a few times and you get a feel for how the bolt is gonna come out. 

 

[Handy Don 13,340]

42 minutes ago, ebinmaine said:

Repeat this a few times and you get a feel for how the bolt is gonna come out. 

 

Nice and easy.....or rough. (Thanks, Tina!)

[Sailman 1,299]

You can get all the gaskets from I Save Tractors....head gasket, valve adjustment cover and carburetor gaskets.

[Wild Bill 633 866]

7 hours ago, Jon Paulsen said:

and maybe a bottoming tap to chase the threads...

FYI, ARP has thread cleaning chasers.