Stihl 361 cylinder / piston woes

[RuffneckDave]

took my 361 out to do some cutting last week.

Fired up and ran for about 5 mins and then locked up until it cooled down.

First its been ran in about 8 months.

new non ethanol gas / stihl mix.

took muffler off and looked and sure enough it was scared up.

Pulled cylinder off and here is what I found

What causes this?
What to check?

New piston / cylinder are in order?

Thanks for the help!

 

[Donnieboy]

My guess would be an air leak. Bad intake boot, hole in fuel line, crank seal.......how was it running before it locked up?

 

[RuffneckDave]

ran fine I would say.

no leak in fuel line, had some pressure in it when I took loose from the carb.

 

[wood4heat]

How old is it? Any idea on the hours?

 

[RuffneckDave]

no idea, was bought used.

Ive had it about 3 years and never any problems from it before now

 

[redoakman]

yikes is that pic of the piston on the intake side

 

[RuffneckDave]

muffler side.

intake side was fine

 

[albert]

Not enough oil or too lean fuel mixture. Was saw stored empty and ran dry?

 

[RuffneckDave]

no

 

[RuffneckDave]

up for more advice, thanks

 

[SteveSS]

Crankcase looks drier than the sahara desert. What was your mix ratio?

 

[RuffneckDave]

50:1

the small mix to a gallon

 

[angelo c]

up for more advice, thanks

Pressure test the heck out of every hose and line in that summabeeech before you run it again(with a new OEM piston of course...but I wouldda done dat before it went topless.)

I'm going with Al on the lean seize as well.
What's the chain look like ?

 

[RuffneckDave]

could use sharpening.

didn't try to cut with it, just fired it up and ran it.

 

[angelo c]

could use sharpening.

didn't try to cut with it, just fired it up and ran it.

Reason I asked is I had a few saws come from a small tree service guy that checked out fine pressure testing and the only thing I could find was that the saws were just "pushed" too hard on questionable chains.
They will be run at 40:1 this season as a test as well.

 

[RuffneckDave]

Good to know.

Explain lean seize please.

Thanks

 

[angelo c]

Fuel mix got too lean, either by too little fuel to air mix ratio, maybe air was introduced by "other then carb" so it's un metered. No way to control mix ratio.
Best I can do at this hour....

 

[wood4heat]

Too lean of an air:fuel mix will run hot, detonate, and reduce lubrication. Three things that are bad for an engine.

 

[spindrift7mm]

Whats the marks in the bottom end last pic, pry bar ?

 

[flehunseos]

Ive had it about 3 years and never any problems from it before now