Is this Husqvarna 120 Mark II Chainsaw Salvagable?

fishchoke · May 12, 2022, 11:15:09 PM

I got this Husqvarna 120 Mark II Chainsaw 2 years ago. It's been used maybe like 10 times. It starts and runs, but will not run under load for more than about 30 seconds. I want to say it acts like it's running lean, gets hot, and dies from overheating, but cylinder head temp is only measures like 180-190°F. It will idle, but only for a few minutes then it'll just die suddenly (usually right before I try to use it). It's always been contrary since the day I bought it.

I've read that piston-cylinder wall scoring is a sign of a bad chainsaw, but the examples I've seen online show alot of scoring. I do see scoring in my saw but not nearly as bad (pictures below), so I'm wondering if this is the end for it. Compression test only gets up to 70 psi (nowhere near 110). Adjustments to hi and lo mixtures seem to have no effect. Carb has been rebuilt and cleaned, no effect.

So, is this thing toast, or is it somehow salvegable?

sablatnic · May 13, 2022, 01:14:37 AM

I wouldn't do it. It could probably be done by installing a new piston ring, filing the piston round again, and cleaning the cylinder of aluminium and carbon, but you would use a lot of time, and you would still not have found the reason for it to score piston and cylinder.

DHansen · May 13, 2022, 07:36:51 AM

In the last photo the cross hatching looks aggressive to me. Not sure if it is just a reflection of the flash or really that much on the cylinder walls.

Was the saw new two years ago when purchased?

Low compression seems to be your issue, but the question would be what caused the damage to begin with.

fishchoke · May 13, 2022, 10:48:33 PM

Possible reasons for scoring I can think of:
1) I forgot to put in 2 cycle oil and ran a tank of oil-free gasoline through it.
2) I used starting fluid to start it up, also oil-free.
But the thing is, this saw had problems the very first time I ran it.
And I know I put in 2 cycle oil the first time I ran it, I remember doing so.

The cross-hatching is not quite as bad in real life as it looks like in the picture.
It looks to me like whoever did the boring at the factory was using a cheap-o machining process.
I'm betting my new vertical scratches are more to blame.
I'm also thinking the vertical scratches came later on, as the saw was much harder to pull-start when it was new than is it now.

Yeah I bought the saw brand new from Tractor Supply two years ago.

fishchoke · May 13, 2022, 10:54:22 PM

Hey maybe I'll try this:
Amazon.com: P SeekPro Cylinder Piston Kit for Husqvarna Chainsaw 125 Mark II 577831102 : Patio, Lawn & Garden
Only $29

First I think I'll disassemble the whole thing and see if the piston ring has welded itself to the piston.
Perhaps I can try to clean up the bore and piston, and then add a new ring.

We'll see ...

rusticretreater · May 13, 2022, 11:09:43 PM

The piston wiggles around in the bore even though the tolerances are close. Once you have scoring, there is no way back. It can only get worse. It tries to weld itself together. As you only have one cylinder, any drag on the piston just kills the engine.

The crosshatch looks fine to me, but scoring is obvious on the cylinder wall. You might have made 50:1 mix when it needed 40:1 or something like that. It may have just been a bad engine to begin with. Too late to do anything about it now.

Seems like you are on the right path now. Just price out the cylinder/piston parts and make a judgement on whether you can fix it and if its cost effective for you. I don't know about the parts you linked. That is an insanely low price so don't expect it to work for long.

Fulcrum156 · May 15, 2022, 10:52:59 AM

when I bought my new 120 mark II it came without having the carburetor set. It would run for a while and then just die. After restarting it it would run again for a while and same as before