Rider smoking

I've got a snapper rider (30" with 10hp Briggs) (rear engine). Today I started cutting my grass when all of a sudden it started putting out whiteish-blue smoke. So bad, it smoked up my neighbors yard. The engine doesn't sound differant at all. It has never done this before. Could you give me some ideas as to what it might be? Whenever I went to empty the grass bag (with the deck dis-engaged) it would stop smoking. Sounds to me like a broken ring or badly scored cylinder wall.

 

It sounds like you are mowing a steep terrace, allowing the oil into the valves which then burns like a stock car race. When you empty the bag on flat ground, the oil is level again and not spilling into the valves and the smoking stops. Does this fit your scenario?

Also, overfilling the oil will cause this even quicker. The oil dipstick must be fully seated in order to read the level. If not, you will get a wrong reading and overfill it.

 

My yard is perfectly flat. With the blades engaged, the higher the speed...the more smoke. Whenever I empty the grass bag...I usually run at top speed...no smoke. The numbers on the engine are m-28A707 t-0122-02 & c-9705232A

 

Well, I'm no lawn mower expert but I'll give it a try. It deffiniatelly sounds like burning oil, so here are some senerios I though up:

-broken piston ring

-broken piston ring land (the sides of the grooves in the piston that hold the ring in place, not something that commonly breaks, but it does happen occationally)

-excessive clearance between valve stem and valve guide allowing oil into cylinder (but unless the engine is very old, you shouldn't have a problem with this)

-pcv (posotive crankcase ventalator) clogged thus not allowing normal piston blowby/crankcase pressure to vent out and thus causing excessive crankcase bressure thus causing oil to be forced past rings and/or valves

-and in the far fetched possibility, the needle valve in the carburetor not sealling (either due to trash on the needle valve seat or a busted float) thus letting gas leak continuessly into the cylinder, past the rings, into the crankcase and mixing in the oil thus raising the oil level to the point that it would leak past the pcv valve (at this point it would probably have a chance to leak around the valve stems and into the cylinder) and continue up the vent tube (being forced by crankcase pressure) into the carburetor and into the engine. But since you said it only smoked under load, I suppose you can rule out this last possibility.

Sorry for being so long-winded, I get excited when I read about engine trouble!!!!

 

It does sound like blowby (excessive buildup of crankcase pressure). The points lugnut and mower17 brought up are valid. Damage to the rings and or cylinder walls would be a pretty good guess. It's pretty easy to take the head off and inspect the cylinder walls on this engine. If the walls look good, then you might check into the PCV system. This is all assuming the oil level is correct and the oil is not gas-thinned.

 

I have the same type problem on my 14.5 model 28707. It seems to be sucking oil from somewhere. Does these small engines have a PVC system and where is it, how does it work.?

 

IF THIS IS A OVER HEAD VALVE ENGINE LOOK TO THE HEAD GASKET IF THE AIR FILTER IS BLACK

 

GmanOle,

Welcome, From your post I will assume your are speaking of a Briggs 280707 or a 281707 Red Hat IC engine. I own one! In either case, your PCV, Positive Crank Case Vent will be located slightly forward and below your carburetor. There is black hose that will run from the carb air cleaner to this breather. This pan type breather is secured by two screws;top and bottom.

The PCV valve has a one way reed valve. This valve will vent crank case gases through to the carb to be burned in the combustion chamber.

On the inbound of the piston this valve closes to create a vacuum in the crank case. This vacuum will prevent excessive oil from entering by the rings and causing excessive oil into the combustion chamber. On the rebound of the piston the crank gases are vented out through the hose to the carb to be burned in the combustion chamber before being vented through the exhaust to the atmosphere.

Without this valve; crankcase pressure would force oil by the rings on the back stroke of the piston and cause excessive oil burning, (blue smoke).

God Bless,
Dave237

 

And it was the head gasket, blown between cylinder bore and pushrod chamber, therefore pressurizing the crankcase and pushing oil out the vent tube into carb intake. I suspect this is a common occurence with this engine configuration. Thanks