MS251 Blowby

[AusLach]

Morning all from NSW, Australia. Thanks for having me

The muffler bolts rattled loose on my ms251 the other day and while I was throwing some Loctite on them, I noticed some discolouration on the piston. Does this look excessive?? The saw still runs hard, and has plenty of compression.

There’s nothing on the piston of my 362 and I run the same fuel mix in both but it has me worried. Any advice/insight would be appreciated, thanks all.

 

[Deets066]

What oil do you use?
Stihl?
Also how are your tuning skills?

 

[AusLach]

What oil do you use?
Stihl?
Also how are your tuning skills?

HP Ultra at 40:1.
Tuning skills are very limited, I’ve been reading heaps here and checking out plenty of YouTube to try and learn more.

 

[Deets066]

Ultra will make mess out of it if running rich.
I’d guess your 362 is M-tronic?

 

[AusLach]

C

Ultra will make mess out of it if running rich.
I’d guess your 362 is M-tronic?

Certainly is. Worth getting it tuned properly you reckon?

 

[Deets066]

I would suggest running better oil and keeping a proper tune.

If you still have the muffler off, roll the piston down and get a pic of the rings and crown area.

 

[drf256]

May be only me, but in my experience most strato saws have that discoloration on the piston, especially if your oil is known to cause coking. Unsure why your 362 doesn’t have it, as it’s strato also.

They just don’t get that wet looking skirt that the non-strato saws do. Yours is a bit more than I normally see, which is probably your tuning and oil/mix.

My 261 and 462 look like that.