STIHL MS271 help wont run.

[Dragcutter]

Hey guys yall are great help. It nice to have such a knowledge resource.
I have an MS271 Farm boss 2 years old. I got it pretty hot and when I let off the trigger it quit. I let it cool down it would not start back. I check it out ant it has spark and fuel. The compression however is only at 90 psi. It was NOT RUN ON UNMIXED. It was run on recommend mix stihl oil and marine gas. Non ethanol.
Looking in the exhaust port and intake I cant see any scaring on the cylinder. Piston looks a little dark but not melted by no means. Rings are dark as well. As for usage it has never worn out the original chain yet.

Questions
What should compression be?
Shouldn’t it run at 90psi?
Could I just have collapsed or weakened the rings?

 

[Matt Coolen]

90 psi is kinda low. Should be up around at least 120 to run decent. Looks kinda dark in there, are the rings stuck? What made it get hot? Saws run pretty dang hot. Maybe had an air leak at carb boot and leaned out on you?

 

[Matt Coolen]

Just watched video. Top edge of piston is showing scoring. I would bet rings are sticking in the lands

 

[Dragcutter]

90 psi is kinda low. Should be up around at least 120 to run decent. Looks kinda dark in there, are the rings stuck? What made it get hot? Saws run pretty dang hot. Maybe had an air leak at carb boot and leaned out on you?

Wellll. I might have put it on my plank mill for a little bit. lol. I just cut 2 6”x16’ cuts.

 

[Dragcutter]

Im thinking I might get by with a piston and rings maybe. What do you think?

 

[Dragcutter]

Oh and with out splitting the case it hard to tell if they are actually stuck but it looks like the could be I agree.

 

[Matt Coolen]

Likely be ok with a piston and rings, have to have a good look at the cylinder walls. If you take a small flathead in through the exhaust, you should be able to move the rings slightly, to see if they are stuck. And yeah... milling, a saw will lean out and get hot, need to richen up your high setting.

 

[Dragcutter]

Likely be ok with a piston and rings, have to have a good look at the cylinder walls. If you take a small flathead in through the exhaust, you should be able to move the rings slightly, to see if they are stuck. And yeah... milling, a saw will lean out and get hot, need to richen up your high setting.

That was it. Cylinder is perfect. Not a mark. Piston is even not terrible. Minor scoring at rings just above the wrist pin. Rings stuck and weak. I am 100% sure a piston and rings will make it like new.
It had 2 days of warranty left. Two dealers said it was trash would cost upwards of $400 to fix it. Last guy said “ you can just leave it here if you don’t want to take it or I will give you 10% off on a new saw for it.
I figured with still carrying 90 psi it stood a good chance of being repairable.
thanks guys!

 

[Matt Coolen]

Awesome to hear

 

[HarleyT]

Looks like running on bad gas.

 

[Dragcutter]

Update. $27 piston and rings.
runs like it was new.

 

[Matt Coolen]

Update. $27 piston and rings.
runs like it was new.

Awesome! Glad to hear. Pretty cheap repair and got some experience to boot!

 

[rupedoggy]

Milling 16 foot long pieces with a homeowner saw?

 

[SteveSr]

Hey guys yall are great help. It nice to have such a knowledge resource.
I have an MS271 Farm boss 2 years old. I got it pretty hot and when I let off the trigger it quit. I let it cool down it would not start back. I check it out ant it has spark and fuel. The compression however is only at 90 psi. It was NOT RUN ON UNMIXED. It was run on recommend mix stihl oil and marine gas. Non ethanol.
Looking in the exhaust port and intake I cant see any scaring on the cylinder. Piston looks a little dark but not melted by no means. Rings are dark as well. As for usage it has never worn out the original chain yet.

Questions
What should compression be?
Shouldn’t it run at 90psi?
Could I just have collapsed or weakened the rings?

Top end is cooked. Check for aluminum transfer on the inside of the cylinder. Yes, you'll find some! This has to be COMPLETELY removed before putting it back together.

Next need to determine (and FIX) why it seized in the first place. Possible reasons...
1. Marine gas was old. Ask the marina how often they get deliveries. Find another source www.pure-gas.org.
2. Carb tuning too lean.
3. Powerhead overload... small saw forced to do milling... dull/wrong chain.
4. Air leak.

BTW, you are CRAZY for trying to mill with this saw!