"My best guess is that the sudden stop cracked the piston and that allows some oil to seem past when it sits for awhile. The other possibility I've thought of is a bent connecting rod which is causing bad piston alignment and messed with the ring sealing."

Naw. Are you sure you aren't overfilling the oil? Parking it with the cylinder down hill, otherwise, the oil level should not be high enough to get into the cylinder.

Walt Conner

Agree with Walt-
Next time you park it after mowing, slide a 2x4 or similar under the wheels on the spark plug end of the mower to raise the cylinder slightly and see what happens.
Start up smoke really isn't anything to worry about. It's the smoke that continues after a couple minutes of running.
On my Honda, if I'm AT the full mark, I get a few seconds of start up smoke. Been doing that for 21 seasons now.

It was slightly over filled with oil. Not much, but apparently there's a point where it will puddle in the cylinder and then seep past the rings. Tipped it over on the side to drain out a bit, and on subsequent startups, no smoke.

Very old post here but why not?

My old briggs tiller has smoked on startup since out of it's box new. I never let it bother me at all as I never have to add more oil. Why not return anyway though, It smokes?

Because it is a known fact any mechanic will back that startup is the worst thing on any engine because everything is dry since all the oil runs down into the pan. Dry starts wear more metal/plastic off moving parts more than any other time ones running! I must say "plastic" too as today's small engines have a lot of it inside.

Now' smoke on startup means you have oil inside the cylinder/head area. That means "something" is being lubed at startup so I'm grateful for the problem it has. Yes, grateful as long as no wet oil or crust buildup on my plug and no top off ever needed between changes. so it's very little oil at all, just a small puff but it is certainly blue & not black which is too much gas!!

So what is a lot?

Myitchybushi car engines that smoke so bad they disappear on takeoff at every stop light smoke most all their life and still they just run almost forever. Even pass local emission tests too...lol

Yes' a little bit of smoke is a welcomed issue in engines but too much is certainly not and I would have sent it back if it was. As long as it stops smoking just after started I'm happy.

It's now been doing it 10 years already! Still no more smoke than seen when new and never added oil between changes. No save the earth people seen out front yet so until then I'll let her smoke some...lol

Oh btw' before anyone says it's not plastic inside today's engines as a retired certified molding tech all you need to know to identify a plastic is any materials chemistry name that starts with "Poly" is a plastic... No ifs or buts about it, it is a plastic! Briggs cam/parts are made from poly-amide-imide. Their trade name on it is Torlon. Companies always call their plastic something other than it's original chemistry name so "Poly" is not involved in the name so people think it's something different or "anything" but plastic especially inside of an engine and worse on a crank/cam.

fwiw: Complete plastic engines are soon coming and I'm very shocked they aren't here already? Because in late 1980's I saw a completed one in a plastics technology book.

It was the plastic industries statement that made us all laugh though.

"Advancements in Polymers (plastic) are now ready for new age engine development, but the oil industries remain behind and until the oil companies advance further to reach our levels a Polymer engine will not be brought onto market."

So' they say it is the oil industry's fault that plastic can't survive the daily punishment of an engine.. Now that was just too funny, but the plastic chemists really do blame the oil chemists for this failure! Our CEO had this made up on a sign for laughs in his office so he could blame big oil for our failures too. lol