Riding mower engine smokes under heavy load

My riding mower started smoking alarmingly yesterday, and I've never seen anything quite like this. It's a 10-hp B&S single, and whenever I hit grass thick enough to cause it bog down substantially, it blew an absolutely enormous cloud of acrid gray smoke. It was a pretty calm day and the second time this happened I was near the road in front of the house. The cloud of smoke remained pretty intact and casually wandered out onto the road. It was so thick, cars were slowing as they approached it.

The first time this happened I shut it down immediately, and each time after that I pushed in the clutch until the engine recovered to normal, so I never let it continue to see whether it was actually going to shut down. And the first time it happened I did check the oil level, and it was full (I had topped it off before starting that mowing session).

I had something similar happen with the same mower a couple of years ago, except it was far less smoke, but that turned out to be the carburetor having shaken loose a bit creating a leak at the manifold, so the second thing I checked after the first occurrence (after checking the oil level) was the tightness of the carb. But it was on tight.

It was a pretty warm day, ~90º, but it's been about that temp most every time I've mowed for the past two months. Start-up seemed normal but this mower does burn 3-4 ounces of oil each hour of run-time.

I do note that I can never seem to get the oil dip stick out with the level clearly indicated so I rely on whether there's oil in the 'Low' and 'Full' holes, and I do tend to err on the side of caution, so it might have been a bit over-full. Is this something that could be the result of too much oil? And of course my chief concern is that this might be an indication of looming serious break-down, worn or broken rings or some such.

Ideas?

 

Probably the oil level. If there is a problem telling how oil you have in the engine because of the markings on the dipstick, drain all the oil out of the engine, then fill it with just the amount the manual says should be in it. Then pull the dipstick and file a small mark at the edge of the stick where the oil shows.

 

3-4 oz/hr is more than normal oil consumption. That is a bout the amount to go from the add mark to full. Sounds like the rings are getting worn. You can check your compression to confirm. Still as long as it has enough compression to run, and you keep oil in it, it should be ok for a while except perhaps under extreme or sudden loads due to lack of power.

 

Unfortunately, the high oil consumption is nothing new. It's been pretty much the same ever since it was rebuilt about 15 years ago.

 

That can happen if not properly broken in and oil type and change after a rebuild.

 

What model engine is on it?

 

I wonder if there may be a problem with the head gasket and getting a blowby in a heavy loaded condition.

 

That's why I was asking the model.

 

Do you think a Magnetic Oil Plug would go very far in minimizing the damage done during the break in period ?

 

In the newer stuff just about everything is aluminum except maybe a cast ring.

 

Cheese, it's a Briggs & Stratton (model) 28V707 (type) 1113-E1 (code) 990515ZD

 

Okay, that's a flathead, so the head gasket leaking and causing the problem isn't an option. I'd go with oil level too full or too much blowby from worn rings creating too much crankcase pressure. If you are using thin oil, go to straight sae30, not 10-30. Fill to the correct level and see if it helps.

 

Just curious cheese, have you seen any and if so how many 10HP Briggs OHV...

 

Thank you, cheese. Sounds more like normal aging process rather than impending disaster, which is a relief.

 

Well, you have the 21r707 for the vertical engines, and then you see a lot of the horizontals like the 205000 series. Most of those are on generators but they are also common repower engines on old cubs, wheelhorses, etc... so yes, they are out there. How often? I don't keep count, but it's not often that I see any 10 hp engine on a mower, period, OHV or not, hence the inquiry.