i doubt anyone is going to be able to speculate without more detail of where the oil is located, under engine? carb side? others side? front or rear? high/low on engine?

"Massive oil leak"....."major oil leak"! As johninmd says, not much info to go on. Though the oil leak becomes a "major", there has to be a point where it is just a "buck private". You may have to watch closely for "that magic moment" when the oil first begins to escape.

Agreed - theres not a lot of good information to work with here.

Based on the info provided - I assume your engine is not smoking badly from the exhaust ?

Is the oil filter tight ? Is the dipstick tight ?

What about putting an old pizza box (card board) under the engine when the engine is off and the oil is topped off.

Let it sit for a few days and see if its slow weeping leak...

You may have to climb under the unit - Or get it up on ramps and see it you can spot the leak with a flashlight.

I had a brand new tractor with a Briggs Intec twin that did exactly that type of leak. It turned out to be a pinched valve cover gasket (mis-installed at the factory). Once the engine warmed up, the hot and slightly thinner oil would push through the gasket and spray on the exhaust pipe. WHOA! Looked massive, was actually a minor leak made to look like a big time problem by all the smoke generated. It was simple to track down once we'd cleaned it up and then sat watching it run. I believe the gasket cost about $1.28 and the repair took 5 minutes.

Still, its hard to believe one could not find where the leak was coming from.

Thanks for the comments. Unfortunately the oil leak starts after the mower is running and I can't find anyone to follow me arond the yard. Sitting on jacks, engage the mower, ran it for 45 minutes and can't get that leak going. dipstick is in, no cracks noted. Have vacum at dipstick, valess wer resone 25 hrs ago. Wonderin if the exhaust is plugged, don't have a leak-down.. Presume that the seal is blown, but not sure of the cause. Any hints would be appreciated. thanks in advance.

Hi, I have the same problem on a Kohler 25hp. Runs great for about 30 to 45 min. I have put in 4 crank seals. Seal are not damaged when removed them. I've Replace both Head gaskets new valve cover gasket have vacum on dipstick,new breather, checked crank end play. I work for Caterpillar Im a engine and Transmission rebuilder, I have not fixed this one yet...I have the same engine in a Kohler generator no problems at all it runs every Monday for 30 min for the last 5 years and longer when power goes out. ??

Replaced new breather reed and gasket? I've seen horizontal twins pump oil due to missing oil cap and dipstick seals. Good word is that you have negative cc pressure.

Hi, it's a vertical shaft, after removing the engine from the mower I wound a crack in the oil pan at the crank seal im going to replace the pan . Thanks

checked head gasket and replaced valve covers and gaskets. iol filter and base tight washed let run with no leaks but when they take and use it it leaks oil . lots of guards to remove . not sure what to do from here its the third time ive had this problem