Next step, troubleshooting Kohler SP27

Tank Driver

LawnSite Member
Hoping somebody recognizes the issue here and can give me the next logical step..

Exmark Lazer Z 72"
Kohler CH740-0045, 700hrs

Mower had been running ok, there was a sense that it was losing a bit of speed over time but it was only used about an hour per week so hard to tell if it was just my imagination.

One day there was a sudden smoke cloud, oil was getting onto engine. Oil Loss did not go below dipstick minimum during incident.

(Cyl 1 spark plugs dry sooty, Cyl 2 plug normal. About twenty hours on those since spring replacement.)

Assuming it was an original head gasket biting the dust at Cyl 1, the revised kit was installed on both, and a shattered intake stem seal was replaced at cyl 1. The head of cyl1 was caked with carbon while 2nd looked good, but I did not attempt to scrub it down (I try to "fix" as little as possible in troubleshooting process to minimize variables).

Test run continued the extreme rate of oil loss. Checking under flywheel, found the crank seal had blown itself out. Replaced.

Next test run found oil leak stopped, I did about 30 minutes cutting, then power rapidly deteriorated. Assumed this to be bad coil acting up from heat, decided to refresh the ignition system- Kohler said use 2570703S Mdi Module Conversion Kit. Installed, engine runs but not cured.

Finally did a compression and leakdown tests, expecting failure at Cyl 1 in some manner. Results:

CYL1: compression 70, 100, 130, topping out at 170.
leakdown 22% @ 75psi

CYL2: compression 60, 90, 110, topping out at 140.
leakdown 25% @ 75psi

For both cylinder tests i listened around exhaust, heads, dipstick, etc and heard nothing notable.

Was surprised to see CYL 1 pass the leakdown, compression number makes sense for all the carbon.

Running on cyl 1 only, the engine is sputtery and vibrating. Pulling opposite sparkplug, cyl 2 runs buttery smooth and maintains higher rpm.

As a quick test for the heck of it, I siphoned out the 87 octane (probably 86 or 85 given a month or two age) and added 93 to test whether it plays nicer vs the high compression at cyl1. No noticeable effect.

I'm leaning toward pulling the cyl1 head and cleaning it up to bring compression back down to normal range.

So now the question- Is there anything in the air fuel delivery design that would disproportionately affect one cylinder over the other, that I also need to look at?


LawnSite Senior Member
Near TMI
Did you look over intake manifold for leaks? Carb problems could be causing the issue also. Maybe try an unlit propane torch around intake gaskets when it starts acting up to see if engine runs better. You may end up removing the #1 head to clean up carbon but it will be easier to troubleshoot if it’s running correctly before removing the head. Good luck.