Outdoor Power Equipment and Small Engines - Lawnboy crankshaft seals

Hi everyone, I've a strange situation here & am hoping someone has seen it before... I have a 2 stroke lawnboy push mower,, Mod CS21ZPN,, Ser J124B0162.. It was brought in with a new plug & no start...It has great spark..I pulled the muffler off to check the exhaust ports & found the seal on the shaft but not in the engine... Just for goofs,,I pulled the flywheel & the seal wasn't in the engine either,, just rolling around the shaft..
I put the seals back & it runs....I now have new seals for it,, But am wondering if the seals blown out of the engine isn't caused by something else??? Any one else seen this on these older Lawnboys???? Thanks Guys..... Roger

When I did snowmobile repair, I did see a couple of seals blown out. Ususally happens to older engines and happens if it a big backfire thru the carb occurs.

That makes sense,, That would be a lot of pressure in the crankcase & since this has reed valves,, the pressure would have to go somewhere... The new plug in it maybe a sign of running problems in the past he was trying to fix... I'll call him for more info...... I Thank You Lots,,, Roger

It can happen if starter fluid (ether) is used to prime the engine, very explosive and can cause the seals to pushed out of the engine. I have also seen this on units where they just came loose and came off, but it's usually only the bottom seal that it happens to.

Thanks 30year,,, The owner said it developed some running problems ""a year or so ago & it would backfire on ocassion"". I measured the old seals & they are 0.007 smaller than the new ones.. I put the new ones in, (with a lite coat of loctite on the outsde of the seal),, Cleaned the carb, Sharpened the blade & the heavier the grass it has to cut, The better it runs!!! Just wear & tear I guess,, Just kinda strange,, Never seen the seals pushed out like that... Thanks too all for the Help.. I owe 'ya one!!! Roger