I bought a Husqvarna 550 XPG as a repair object and I dismantled it to check its condition. It turned out to have seized on the exhaust side, and the piston ring was stuck. There was a great deal of oil and soot, so it had likely been running with an overly rich oil mixture or the wrong type of oil. A new cylinder and piston have been ordered, so hopefully, it will be a working chainsaw again.
Husqvarna 550 XPG seized
- Thread starter V70tdi
- Start date
Nice project to have.
Wow! That pistons a mess. Equal gouging on the rings too.
CleanSump
Site Donor 2026
Back in the good old pre-synthetic days changing rings, pistons, and reed valves was common and parts were cheap. Today is a disposable mindset society. Don't fix things. Use it, throw it away and get a new one.
Kind of like "Why change the oil? It's a lease; I'll get another in 3 years."
Kind of like "Why change the oil? It's a lease; I'll get another in 3 years."
Did the intake side get scored too? That one is odd as I don't see the usual black/brown spot from oil breakdown. OE or aftermarket for the new parts? Looks like a fun resurrection.
Possible that it was cold seized. Or just run hard while set lean. The newer 550xp mkII is auto-tune. I don't know if that 550 was just a plain carb that was lean. I use a tachometer to set my high jets. The auto-tune doesn't need anything.
Exhaust side only. Aftermarket parts for this one with a promise from the shop that its good quality parts so I will se how it ends
This is a auto tune. Here in Sweden all 550XP has been delivered with auto tune.
Nice!
Also then it may have been run on straight gasoline, then they tried to see if it be ok on 2 cycle.
I think i might look at the connecting rod bottom to make sure its not scored too.
That’s a fun project! The 550 XP is definitely worth saving. It's hard to say for sure, but before you finish the rebuild, make sure to inspect the muffler for any debris or internal issues. Please keep us posted on how it runs once you get it back together!
That is not likely to be from too much oil. That appears to be a classic 'no-oil' situation.
A 4 corners seizure is generally insufficient warm up time.
A top of the piston seizure is often indicative of a too lean condition.
But no oil most often results in complete damage, like we see here.
As always, just a guess. There are times where the pattern is not set in stone.
Here is what a typical 'too lean' situation looks like:
And a classic 4 corners seizure, often from insufficient warm up time. Always take your time warming up a two stroke. Blip the throttle giving time for temps to equalize.
A 4 corners seizure is generally insufficient warm up time.
A top of the piston seizure is often indicative of a too lean condition.
But no oil most often results in complete damage, like we see here.
As always, just a guess. There are times where the pattern is not set in stone.
Here is what a typical 'too lean' situation looks like:
And a classic 4 corners seizure, often from insufficient warm up time. Always take your time warming up a two stroke. Blip the throttle giving time for temps to equalize.
Just another note about piston seizures on two strokes. Any reasonable oil ratio and quality oil will work. However, insufficient octane can result in inaudible detonation, causing the piston to expand excessively and grab the cylinder. The most reliable way to operate a high performance two stroke is to use high octane non ethanol fuel and between 32 to 1 and 50 to 1, jetted properly. I use VP C9 unleaded race fuel.
Using 87 octane can be on the low octane edge for chainsaws.
Using 87 octane can be on the low octane edge for chainsaws.
