Stihl MS 261 chainsaw low compression what to replace

[Jonny Vee]

I purchased a second hand Chainsaw ms 261. it start at first pull and accelerate just fine. I checked compression and seems to be only 125PSI when usually is over 170psi when new

Would you just leave everything as it and keep using or should I replace piston/rings or just rings?

Any advise?

 

[Burnerman]

Pop the exhaust silencer off and have a look at the piston / rings / barrel state.
The compressions aren’t that bad really so I’d just go for a piston and rings at this stage.
You should find pattern parts st GHS Ltd.
There’s no huge hurry as the saw seems to be going well enough - if it was difficult to start then it’s time for action.
John

 

[Jonny Vee]

Pop the exhaust silencer off and have a look at the piston / rings / barrel state.
The compressions aren’t that bad really so I’d just go for a piston and rings at this stage.
You should find pattern parts st GHS Ltd.
There’s no huge hurry as the saw seems to be going well enough - if it was difficult to start then it’s time for action.
John

Thanks John

As you suggested, I will put some hour of work into it and then will go for piston and rings.

Are the GHS non genuine parts reliable and long lasting?

 

[Burnerman]

GHS do many pattern parts and genuine ones, but they do state what you are getting.
I've used them for years now - including many piston and barrel kits - and have had no complaints at all. When you consider the genuine price of Stihl parts, it's often near machine write off time.
L&S Engineers are another good firm.
John

 

[Jonny Vee]

GHS do many pattern parts and genuine ones, but they do state what you are getting.
I've used them for years now - including many p

iston and barrel kits - and have had no complaints at all. When you consider the genuine price of Stihl parts, it's often near machine write off time.
L&S Engineers are another good firm.
John

Thanks John, I have used L&S but for genuine parts only. I agree the genuine engine are too expensive.

Stupid question do you usually beed to replace piston or rings are just enough to get some higher compression back?

 

[Burnerman]

It really depends on the amount of vertical scratches that you can see.... they all will reduce compression to a degree.
In normal wear, the piston suffers the worst as it tends to ‘rock’ in the barrel and shows wear on the thrust faces. There won’t be any wear on the faces that the gudgeon pin is on.
Therefore it can make sense to replace it, but of course if there is scoring on the barrel then that can’t be overcome.
It’s always good to see the piston rings moving in their grooves - they will be brightly polished whilst the piston is more of a matt colour.
John

 

[Jonny Vee]

It really depends on the amount of vertical scratches that you can see.... they all will reduce compression to a degree.
In normal wear, the piston suffers the worst as it tends to ‘rock’ in the barrel and shows wear on the thrust faces. There won’t be any wear on the faces that the gudgeon pin is on.
Therefore it can make sense to replace it, but of course if there is scoring on the barrel then that can’t be overcome.
It’s always good to see the piston rings moving in their grooves - they will be brightly polished whilst the piston is more of a matt colour.
John

Thanks John, only made the question thinking to genuine parts as the rings are affordable but piston still goes around £90. Make sense to replace piston and rings using patterns parts.Will use this advise for future reference too. Appreciated

 

[Burnerman]

No worries mate, heat the piston up with a hot air gun and the gudgeon pin will just slide out.
Always use the new circlips that come with it though!
John