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kawasaki blow by

C

cole in mo.

Well-known Member
Neighbor has this JD 425 mower with the Kawasaki 20hp horz liquid cooled engine. Its got 170lbs compression on each cyl, but its got very excessive pressure in the crankcase. Its got so much it blows the dip stick out, and if you remove the filler cap, it blows oil all over your hand. The tube going to the air cleaner is open, and oil blows out of it too. I can see if the compression was low, (bad piston or rings) why that would happen. But with the compression good, what is causing the excessive pressure?
 
I would need to see the engine diagram.

If overhead valves, I would suspect the PCV valve first.

Then, I would suspect the head gasket is broken.

Briggs OHV have the same symptoms when the head gasket blows thru. Compression goes into the crankcase.
 
Its overhead valve, and I would suspect a blown head gasket to cause high pressure in the crankcase too, but with 170 lb's of compression in both cyl's, its hard to figure that's the problem.
 
Try doing a cylinder leak down test. Remove the rockers so the valves will be closed, adapt an air fitting in the plug hole and pressure up the cylinder. Listen for air leaks. If air blows into the crankcase, its rings or head gasket.
 
Got in a hurry, need to clarify...

With the valve covers off, and the cylinder pressured up, if the head gasket is leaking into the crankcase, you should be able to feel and hear it blowing into the push rod area.

Also, there will be "some" leakage past the rings. A little hiss is normal, not major blowby, or difference between the cylinders.
 
Backed the valves off, pressured the cyl's, can hear very little going past the exhaust valves on both sides, but nothing to notice from the crankcase.
 
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