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Small Engines (Lawn Mowers, etc.)/Kohler engine crankcase pressure blows oil seal


I have a 25hp OHV Kohler Command series engine on a Grasshopper lawnmower. The engine has about 1200 hours on it, and runs without missing or using oil. Recently while mowing, large amounts of oil appeared. I shut it down immeadiately. After inspection, I found that the rear oil seal had come out. I disassembled far enough to replace the seal, and reassembled. The engine started right up, ran as normal at low speeds, and I tried mowing again. After about 15-20 mins or so of mowing, the seal blew out again. I DID NOT replace the seal with a new one, just put the original back in place. It did not appear to be worn or hard. Is it possible this is just an issue with the seal itself, or is it more likely to be an issue with crankcase pressure? I've seen where the crankcase breather on these engines can become plugged, but would this cause the seal to be blown out? I am very mechanical, but I just don't have much of anything as far as testing equipment goes. Is there any way to tell if the seal should be replaced? Should I replace it and try again? Or should I disassemble farther and check the breather?

Replace seal and check breather.  A breather is like a PCV valve allowing the engine to form a vacuum so the oil stays inside the engine.  You can make an inexpensive manometer or purchase an inexpensive vacuum gauge and a rubber cork to check the engine vacuum.  It MUST maintain vacuum or it will blow the seals and oil out of the engine.


Small Engines (Lawn Mowers, etc.)

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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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