Kohler M12 condition. How to determine?

[jeepdan 321]

Hi everyone,

I'm new to the forum.

I noticed that my 1989 312-8 (that I have owned since new)  seemed to labor much more this summer while cutting grass, and was harder to start after sitting for a week or so.

Engine doesn't burn any oil at all that I can tell.

How can I determine how close it is to overhaul time?

Cylinder leak down test?

Oh yea, after reading through the service manual on this website, I learned that I should have been checking valve lash, something that I have never done.

Dan

[953 nut 51,536]

Sluggish operation could be as simple as a fuel system tune up. If you have been running gasoline that contains ethanol the fuel system will deteriorate. A new spark plug along with new air filter, fuel line, fuel filter and a good carburetor cleaning may be all that is needed.

using ethanol free gas will go a long way toward keeping it running strong.   https://www.pure-gas.org/

[Achto 26,505]

 

If you have never had the engine apart, now might be the time. Before you do a complete tear down, start simple. Pull the cylinder head off and clean all the carbon off from the inside of it. Carbon can cause pre-ignition. As long as the head is off you can pull the valves and lap them and check the clearance on them. Also inspect the cylinder wall for wear and make sure that your cooling fins are clear of obstructions.

[JoeM 7,608]

Adjusting the valves can help, along with a good cleaning and new plug.  Something else to chew on if those items don't cure the problem.  I have found a new magneto worked wonders. I am not sure why, I know they test out and run but seem to make less spark for some reason causing hard starts and sluggish performance.

[oliver2-44 8,836]

As stated above, start small and go through all the fairly simple things. If you haven't had a need to do much maintenance other than oil changes since new in 89 (30 years), it might be a good time to do what I call a minor overhaul.  I'm in the process of doing this on a new to me old C-81 tractor, which  was a non runner.  Pardon me for writing a long list, but I'm documenting this for myself, and for you and others since its fresh on my mind.

 

1. Install new spark plug, start tractor and check it it made a difference.

2. With tractor running spray carb cleaner around base of carb and top of carb throttle shaft to check for air leaks. (if engine speeds up there is an air leak which effects performance)

3. Check fuel pump output (with hose to carb removed , open hose should spurt gas noticeable with each pump) a weak pump can be a symptom of hard to start after sitting a while.  

4, Clean fuel tank & check shutoff valve body and strainer isn't partially plugged (i have found the body of the strainer can get scaled up so I hand ream it with a drill bit, or just replace it)  If you pulled gas tank to clean now is a good time to clean all around transmission and notice any leaks which might indicate a transmission seal needs replacing

5. While replacing hoses   with both hoses off pump, now is a good time to spray carb cleaner into each side of pump, sort of to flush it out. (try to get ethanol resistance hose)

6. With carb still installed) Pull the bottom bowl, if its full of gunk  move to pulling carb for a full disassembly cleaning, if bowl is clean or only has a slight amount of trash pull idle and main jet needle screws and spray carb cleaner through them. (As part of pulling jet screws, count the number of turns inward they will go until they stop so you can reinstall them in the same position) 

 7.Run tractor and see if fuel system work  improved running

8. If not much improvement,  pull the tractor hood, most of this work is on the front of the engine and this make sit so much easier.  (Pull battery cable for safety)

Pull the carb and since it is off do a full disassembly cleaning.  if throttle shaft is worn (wobbles or found during air leak test, install a bushing in the recess at the top of the carb.  Kohler makes a bushing for this but they are a little hard to find in stock. I stack 2 brass thrust washer I get from ACE Hardware in all those little drawers (Hillman part#  58087) Test the throttle shaft fit and if tight hand ream very slightly with a drill bit

9. With the carb off now is the time to get to do head and valve work.

10. Pull head and decarbon head and top of piston

11. Pull valve cover and internal baffel (note position of cover and baffle as they must be reinstalled in the same vertical position to vent properly)

12. Pull valves, and clean (I decarbon them using a wire wheel on a bench grinder)

13. check valve stem diameter for wear and install in valve guide and check for excessive ear (wiggle)

14. Lap valves and check, adjust valve clearance

15. Measure cylinder wear top, and bottom of stroke (and compare to Kohler spec sheet

16. Drain engine oil, fill with diesel or kerosene, crank engine over for a minute to wash everything inside, drain ((I jack tractor to tip it slightly to the side to  make sure all the diesel is drained out), refill oil 

17. Reinstall head, with new gasket torque per Kohler spec sheet now, and retorque hot, after running engine 15 or so minutes

18. With engine tins off, use an air blow jun and blow/clean behind flywheel and all cylinder cooling fins

19. Now is a good time to find the timing marks on the flywheel. I sand and paint the area white, then when dry use a paint pen to mark the Timing mark and TDC mark

20  Reinstall engine tins and battery cable.

I also service the transmission as part of my minor overhaul

With tractor operational

Drain transmission (jack up front of tractor to make sure oil trapped in front of hump drains out

(If oil showed indications of water or excessively dirty (milky, brown or white color, or clear water) 

Fill transmission with diesel or kerosene.  Drive tractor around, or jack up and run through all the gears)

Drains transmission again being sure to jack up to drain area trapped by hump

 Refill transmission with gear oil.

Replace shifter boot if cracked/broken/missing

 

Parts Possible Needed

Spark Plug

Air cleaner (if needed)

Fuel hose and if needed new clamps 

(optional) tank shut off valve with filter screen  and rubber tank bushing

Carb cleaner spray can

Carb base and air cleaner gasket

carb overhaul kit

If needed, fuel pump overhaul kit, or new mechanical or electric fuel pump

If carb throttle shaft is worn 2 Hillman brass washers part#  58087 (or you may decide to buy a new aftermarket carb)

Valve cover gasket, mesh filter, red rubber spacer, baffel gasket

Head gasket

Diesel or kerosene

Engine oil

Valve lapping compound and valve suction cup stick

Transmission gear oil

Shifter boot

Anti-seize compound (I like to put this on head bolts and any bolts/nuts in hot area

 

 

Edited November 26, 2018 by oliver2-44

[953 nut 51,536]

7 minutes ago, oliver2-44 said:

Pardon me for writing a long list, but I'm documenting this for myself, and for you and others since its fresh on my mind.

That is an outstanding list of component tests in a very logical sequence.            

[The Tuul Crib 7,332]

6 hours ago, 953 nut said:

Sluggish operation could be as simple as a fuel system tune up. If you have been running gasoline that contains ethanol the fuel system will deteriorate. A new spark plug along with new air filter, fuel line, fuel filter and a good carburetor cleaning may be all that is needed.

using ethanol free gas will go a long way toward keeping it running strong.   https://www.pure-gas.org/

[jeepdan 321]

Thanks everyone for the warm welcome.

Other than yearly oil changes, spark plug, and air filter. The engine has been amazingly dependable. Only repairs that I have had to do, has been a fuel pump about five years ago, and rebuilding the carburetor a few times due to the float needles wearing out.

 

I will start with cleaning, and overhauling the carb,  as it has been probably ten years since I last done that.

And I will remove the head to inspect things, and do some valve maintenance as you all have suggested.

 

I have been collecting parts for awhile to give the tractor an overhaul / facelift. 

Just wondering if I should go ahead and give the engine a complete overhaul also.

 

Thanks, Dan

 

[jeepdan 321]

I decided to remove the cylinder head today to have a look inside.

First off, I found about two inches of the insulation chewed off of the spark plug wire under the shroud, along with a mummified mouse.

 

The cylinder still had very visible cross hatch, but some light scoring on the side opposite of the valves. Not deep. but sharp enough to easily snag my finger nail.

Measuring the cylinder with the piston at the bottom of it's stroke, showed no taper and  only .001 out of round (and that was measuring off of the scored area.

 

Valve lash was still .017 on the exhaust tappet, and .007 on the intake tappet. Not bad for 29 years use without checking them LOL

 

Now for the bad, resting a dial indicator on the edge of the valve heads, I could move the exhaust valve sideways in it's guide .027 and the intake valve.012.

[oliver2-44 8,836]

On the 312-8 I redid for my son a few years ago I had some valve stem/guide wear. Since the cylinder bore looked good I installed new valves and used coarse then fine lapping compound  to lap the seats . I kept the valve old valve guides. That removed over half the side to side play since half the wear was on the stems. It runs great with no smoke from valve guide oil leakage.  Someday in the future when it needs a full bore overhaul I’ll replace the valve guides.  

 

So I would suggest pulling the valves and measuring the stems 

Edited November 28, 2018 by oliver2-44

[jeepdan 321]

Thanks,

I will remove the valves and measure their stems, and the guide bores to get a better idea of what is worn out.

I was just reading the service manual to see how to remove and install new guides if I need to.

Edited November 28, 2018 by jeepdan

[jeepdan 321]

23 hours ago, jeepdan said:

Thanks,

I will remove the valves and measure their stems, and the guide bores to get a better idea of what is worn out.

I was just reading the service manual to see how to remove and install new guides if I need to.

Both valve stems measure the minimum diameter.

Intake valve guide bore is perfect at .3125 ID

But the exhaust valve guide .317 ID at the largest point, which puts the clearance out of spec.

So, new valves and an exhaust valve guide is going make a good start.