kohler gen set has excessive air pressure in crankcase, normal?

[BigNormitasca]

Ive got a kohler k321 and i was diagnosing some erratic idling and stalling problkems.  I started hearing suction thru the valve cover breather.  From my experience which is limited to car engines i thought the rings had excessive blow by and the compression gasses were going into the crankcase.  But with the head off the engine im still getting that excessive air pressure coming out of the valve cover.  When i crank it you can hear it sucking air in and feel the air pressure coming in and out of the breather on the valve cover.  Since the engines not making compression with the head off is this supposed to have crankcase pressure like this for the oiling system or something.?  Any thoughts would be appreciatted.

 

[RoyM-WO]

Erratic idling indicates a fuel delivery or air intake leak. Check for a worn throttle shaft as well as mung in the carburetor assuming you are running on gasoline. I am not familiar with propane systems.
A healthy engine will have a slight vacuum in the crankcase while running, air will come out of the breather but should not enter. This what keeps oil where it belongs. Disassemble the breather, the blue metal valve should seal against the holes in the body. If it is lazy turn it over.

 

[BigNormitasca]

I rebuilt the carb . The air pressure is so much that if I crank the engine for a few seconds then stop amd pull the dipstick out oil shoots out of the dipstick tube.  Not like oil that was on the dipstick and fell off but there is actual pressure behind the dipstick that's released when I remove it. And that's with and without the head on the engine.  I disassembled the breather cleaned and replaced it exactly how it came apart.  I will try flipping the blue metal peice over and see how it goes. Because what I did made no change in the problem. Will update shortly.  Thanks Roy

 

[John From Detroit]

How many cylinders?  if it is a single cylinder then yes even with the head off there will be compression on the crankcase side of the piston so it will suck/blow/suck/blow as the piston moves up and down.

I think you need to get up to at least 4 cylinders to eliminate this.

WHY.  Pistons are dual acting. they not only compress on the HEAD end but on the crankcase as well so unless you have one moving up as the other moves down there will be "Breathing" on the crankcase.

 

[kdbgoat]

The K321 has a reed type breather valve. It may be gummed up and stuck closed. Pull it apart and clean it up. Use new gaskets (yes, they are still available), and make sure you pay attention to how it came apart so you can get it back together correctly.

 

[BigNormitasca]

Cleaned and flipped the reed as first suggested and that solved the issue.,  I can feel air pressure coming out of it but no suction going back in.  On another note i replaced the head gasket, rebuilt the carb, and set the points and that generator roared to life and runs beautifully now.  No surging or stumbling.  Smooth and consistent idling.  thanks for the help

 

[kdbgoat]

With regular oil changes, with quality oil, those old Kohlers will run about 2500 hours before needing rebuilding. The hard part of the rebuild is the balance gears. Many with garden tractors just leave them out, but that could leave a bit to be desired when running underneath the floor of an RV.