Small Engines (Lawn Mowers, etc.): Briggs Stratton 3.5 HP Engine, valve stem seals, briggs stratton

Question
I just acquired a coleman generator (Powermate 1850) using a Briggs & Stratton 3.5 HP engine. I can't read the model number without tearing all the covers off, but I think it may be a model 91202-1016.  That is from the owners manual. It had a broken rod, because the person who bought it didn't put oil in it.  The rod was replaced by a friend of his. The unit runs great, BUT it spits oil out the breather tube and fills the air filter with oil until it starts running out the air cleaner onto the ground after a few minutes of running.  I removed the air cleaner, and disconnected the breather and there is quite a bit of air pressure coming out the tube.  (With oil).  Sure would appreciate any advice that might save me tearing the engine all apart. Compression is running 85-90 pounds with a compression guage.  Is this too low, or about normal?  Thanks in advance for your time/help.  Marc

Answer
Hi Marc,

The compression is low.  Not low enough to prevent running but not the 125 and up, that is normal for a rebuilt engine.  It is probably low because of the leaking, which is causing the crankcase to become pressurized.  I would check the valve stem seals and the piston rings and cylinder walls.

Let me know how you make out.
Michael