I have an Ariens riding mower model 936042-00 powered by an B&S engine 406777-0442-B1. It has always been well maintained but gets a good work out. It mowes about 2.5 acres each cut. Last year all of a sudden it started to use excessive oil. By now it's about a half a quart to do those 2.5 acres. There is no excessive smoke coming from the exhaust or burnt oil smell in the air, there are no oil leaks or drippings on the floor. But both spark plugs barely make it through the mowing session, By the end of the 2.5 acres they are pretty much fouled up to the point were the engine starts having difficulty running. When I pull the plugs they are a mess, they are black and totally cloaked up with oily crud and sod. So I clean them and put them back and everything is fine for another mowing. Engine runs great without missing a beat. I checked the compression and it was a 130 on both cylinders. Does anybody have a clue what could be the problem with my engine?

I'm not much of an expert, but I seen that no one replied to your post-
Make sure no debris is getting through the system to gunk up things-replace Fuel filter, air filter, oil filter(complete oil change), and clean your carburetor. Be sure to use fresh clean gas.
Make sure that your engine is well cleaned with no debris caking the engine fins and air gaps for cooling.
All the extra grass/leaves will make your engine over heat.
(My mower had "air gaps" for cooling that I never knew existed!)
Hope this helps!
 
 

I am absolutely surprised by the lack of responses or comments on this forum. I always considered this forum the premiere number one source of knowledge when it comes to everything "small engines" but apparently I am wrong. I am sure that my engine problem is not something isolated or unusual but a rather common occurrence as engines rake up hours. 36 views and nobody has a clue what it could be. Well, I guess I have to dig into it and find out myself.

I usually get updates for new posts but didn't for this one for some reason...
 
Anyway, from what you post, oil is getting into the combustion chamber.
 
I would suspect gummed up oil control rings OR compression rings allowing
compression to push past them. Crankcase pressure builds and that oil is pushed
into the breather tube and subsequently burned off..
 
I suspect you'll have to dig much deeper specifically at the rings, head gaskets, block wear..
 
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Thank you SRT. Here is what I did so far. I removed the heads and I found both head gaskets to be in good shape. Also the valve stem seals seem to be tight and snug and the valves themselves virtually have no excessive play in their guides. The top of the heads are black with caked on soot and somewhat lesser are the tops of the pistons. (See pictures) If there was a problem with the piston rings would I still have that good a compression on either cylinder 130 +/- 2? Do you think I should put the heads back on and do a leak down test? Would that tell me more? Thanks Rick

I usually get updates for new posts but didn't for this one for some reason...
 
Anyway, from what you post, oil is getting into the combustion chamber.
 
I would suspect gummed up oil control rings OR compression rings allowing
compression to push past them. Crankcase pressure builds and that oil is pushed
into the breather tube and subsequently burned off..
 
I suspect you'll have to dig much deeper specifically at the rings, head gaskets, block wear..

This site is acting crazy.
 
On my "alerts" for new posts, it shows (copied below) your response but NONE on this site...
 
Quote:
 
Thank you SRT. Here is what I did so far. I removed the heads and I found both head gaskets to be in good shape. Also the valve stem seals seem to be tight and snug and the valves themselves virtually have no excessive play in their guides. If there was a problem with the piston rings would I still have that good a compression on either cylinder 130 +/- 2? Do you think I should put the heads back on and do a leak down test? Would that tell me more? Thanks Rick
 
End quote.
 
A leak down test would show how well the rings, valves, etc  are sealing, (of course).
I suspect their sealing just fine (compression shows us that), but does not tell us anything about the 
oil rings.  
 
You've done / checked about everything on the top end and ruled that out.
 
Besides the time to pull the engine, you'd only need a side cover gasket 
AFTER pulling the side cover, pistons and rings out.
 
I'd check that as your that deep and it really isn't much more to do
(as you seem to be fine with mechanicals)...
 
...

Yeah, I guess something is screwy with this site. On my last post I went into "Edit" to add the pictures and when I posted the edit it said "Approval pending" and it still says it now even though I can see my post pictures and all. So you say, I need to pull the engine in order to remove the pistons? And since it is a vertical shaft engine do I need to drain the oil? I will have to if I have to pull the engine, I guess.

I removed the flywheel and now I can see that my idea of accessing the piston rods through the top is a no no. The top is all one piece. Looks like the engine needs to come out unless I can figure out a way to remove the sump from the crankcase by jacking up the mower. This is my story, always the worst case scenario. Oh well!

The parts diagram for your engine:
https://jackssmallengines.com/jacks-parts-lookup/manufacturer/briggs-stratton/briggs-stratton-engine/400000-699999-series/406700-to-406799/406777-0442-b1
 
And yes, you are correct, the engine has to come out and the sump cover removed(oil drained too).
If you don't have shop manual, use the parts diagram to see how things go together, etc.
 
Once the cover is off, you can remove the cam and have access to the connecting rod bolts. 
Pistons will then come out after that.
 
Do some "You Tubing" to get an idea what your getting in to.
 
 
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