How to Check Crankcase Pressure on a Kohler, Briggs & Stratton, Tecumseh Lawnmower Engine



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**Always follow the instructions in your repair manual when doing repair or maintenance work on Outdoor Power Equipment. Manuals can be found at the manufacturers website.**

In this video I show how to check if your lawnmower engine is creating a vacuum in the engine’s crankcase when the engine is running. When the piston moves up and down, the crankcase volume is constantly changing. This change causes the crankcase pressure to change, but because the crankcase breather valve will let gases in the crankcase escape, but not let air in, the pressure in the crankcase should be less than the ambient pressure.

If your crankcase breather valve is not working correctly, it can cause the pressure in the crankcase to rise. Also, a worn engine will let combustion gases escape past the piston and enter the crankcase. This is called “Blow By” and will cause the pressure in the crankcase to rise.

Increased pressure in the crankcase can cause excessive oil consumption as well as other problems.

Thanks for watching!

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11 thoughts on “How to Check Crankcase Pressure on a Kohler, Briggs & Stratton, Tecumseh Lawnmower Engine

  1. That's really interesting. I guess I had a fundamental misunderstanding as to which way blow-by gasses move. I always assumed small volumes of blow-by are normal, and pressures are positive. You've proven my pressure assumption wrong.
    On my Kawasaki 4-stroke Vulcan, I get a small volume of oil from a blow-by relief tube, right from the day it rolled off the assembly line. What creates the suction? If a blow-by tube flows to atmosphere, how does that sit with the notion that pressures are low?

  2. Bear in mind that if the drilled hole is not bone crushing tight with the stem, air can be sucked in affecting the reading.

  3. If the hole in the rubber stopper is drilled even a tad too large, air will be sucked down into the sump between the stoppers inner wall and the metal guage stem, & affect the reading.

  4. Thanks for all the great videos. I have a 2012 Briggs 205cc 900 Series Intek OHV, no dip stick tube. I put the gauge in the vent opening on the valve cover, will that work? My reading was a slow increase up to 3PSI before I pulled the gauge off.

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