I finally got around to taking a closer look at the Kohler KT-17 on my garden tractor. As mentioned in my previous post, it smokes a lot while running which means oil is getting sucked into the combustion chamber and burned. Combustion products are also getting mixed in the oil which isn’t good.
I pulled the tractor into the garage and started removing stuff to get to the motor. This gave me a good change to take some pictures of it.
The picture below shows the pulley for the front PTO. It is engaged by moving a lever which pushes the pulley into the clutch plate. When it is disengaged it pushes against a brake pad which keeps it from moving.
I found it best to remove all the shrouds before lifting the engine. After that I disconnected all the wires and removed the four bolts holding it down. Finally, I used the engine crane to lift the motor as it weighs about 130 lbs according to the service manual.
I decided I wanted to be 100% sure that I was getting leakage by the pistons. I realized I could turn my end-of-hose pressure tester into a leak down tester by putting an orifice before the gauge. I was able to convert it by turning a plug with a 0.04″ hole in it and pressing it into the male quick connect adapter. Using another adapter, I screwed the tester into the spark plug hole, brought the piston to top dead center, and let the air flow. I set my tank’s regulator to 30 psi but there was so much leakage my tester read 10 psi. Typically you want leakage less than 10%…I have 66%! I checked the other cylinder with similar results. I could have also done this test with the engine still on the tractor but didn’t think of it.
A leak down test can also tell you where the leakage is occurring. Baring a crack, there’s only three ways out of a cylinder: the intake valve, the exhaust valve, or by the piston into the crank case. I was able to feel air rushing out of the breather and dip stick tubes. Normally, you’d put your ear near the carb/throttle body, exhaust pipe, or oil cap to try to hear the leak.
Getting to the pistons is pretty simple on these engines. All you have to do is remove the nine bolts that hold the head on.
With the head off you can see the piston top and the valves. The carbon build up on the valves is due to burning oil.
I touched the piston and found that it rocked which is a bad sign. The two following pics show the rock caused by pressing on the top and then the bottom of the piston. Rock is caused by a large gap between the piston and cylinder wall.
I moved the piston back down the bore and measured it with an inside micrometer. According to the service manual, the bore is 3.125″ when new. It has a max wear value of 3.128″. I measured cylinder #1 at 3.137 and cylinder #2 at 3.136. That’s 0.012″ and 0.011″ of wear in cylinders #1 and #2 respectively.
Unfortunately, this much wear means I’d need to rebuild the motor to get it running well again. At a minimum I’d need two new pistons kits, the bores machined, and required gaskets. I looked around online and found that a single piston kit which contains a piston, wrist pin, and rings was $150. I’d need two of course. I’m guessing this would put me around the $450 mark assuming I don’t run into any other problems which I probably would. I’m not going to spend that much on this motor and am planning to find another motor for the garden tractor.