Seized chainsaw

[Snobdds]

There are a lot of reasons why a saw can be damaged siezed or run hot other than oil mix.

Oh...

Lets review

A saw can get hot, but if it's still getting gas and oil...it won't seize. The saw is air cooled and the fins are still providing cooling even if it's running a dull chain. Its not like a car where coolant provides the cooling...

A saw siezing is really only due to no lubrication and that means straight gased.

 

[Doughknob]

My Husqvarna 570 seized during firewood cutting. No compression. I put atf in the cylinder and waited 48n hrs. Now there's 100 psi compression, good spark bot won't start. Looks like some atf still in the cylinder. Its coming out thru sparkplug hole and muffler when starter is pulled. Not much... I think that's a reason for not starting. Is there way to get it out completely? Anything else to look for?

You had me fooled there for a bit. "No compression" means the piston moves but you get no pressure at the top of the stroke. You actually mean you could not even move the piston, right?

Dull chain?

Nope. My neighbor and I are the kings of dull-chain sawing and we, also, have never seized an engine. Sooted up the mufflers, seized chains to bars, threw chains.......... but never seized an engine.

 

[BnRidge]

and that means straight gased.

Or, carb set too lean, leaking crank seals or gaskets, broken internal parts such as rings, a rod snap ring that comes loose, flaked nichrome finish maybe from a previous rebuild, carbon buildup. What are some others, electronic control malfunctions, air filter plugged - . It's got low compression, get a look, diagnose it, fix and try to keep it from happening again.

 

[MossRoad]

A gas 2-stroke engine seizure can be from overheating, improper gas/oil mixture, lean condition, restricted exhaust (causes overheating, too), cold start to full throttle, some part getting sucked through the cylinder or crank case, several issues.


For example, start that cold engine at full throttle. RPMS go through the roof, the piston heats up and things expand faster than the diameter of the cylinder and PINNNG! you're saw is seized. You had the proper fuel/oil ratio. You had the proper air/fuel ratio. You had proper lubrication. You still seized the engine.

 

[Snobdds]

In the first post, he said it siezed during cutting.

 

[MossRoad]

Improper piston/ring/cylinder wall clearance, too.

 

[jyoutz]

A gas 2-stroke engine seizure can be from overheating, improper gas/oil mixture, lean condition, restricted exhaust (causes overheating, too), cold start to full throttle, some part getting sucked through the cylinder or crank case, several issues.


For example, start that cold engine at full throttle. RPMS go through the roof, the piston heats up and things expand faster than the diameter of the cylinder and PINNNG! you're saw is seized. You had the proper fuel/oil ratio. You had the proper air/fuel ratio. You had proper lubrication. You still seized the engine.

After 40 years of working around loggers I have never seen or heard of such a thing. Everyone starts and runs full throttle during cold or warm weather. The only saw motors I’ve ever seen seized was due to lubricant failure.

 

[Root Cause]

I had a tree sit on mine last year. It seized up and I don't think lube had much to do with it. Just sayin'

 

[Snobdds]

I had a tree sit on mine last year. It seized up and I don't think lube had much to do with it. Just sayin'

I think the tree sitting on it had everything to do with it.

 

[ericm979]

Moss's list is right. "Cold seizure" is possible on two strokes. It's not common though. The piston will have characteristic scoring on four places where the thick part of the piston that holds the wrist pin ends.

In this case it's not the cause since it seized while cutting. No oil in the gas, running lean due to poor carb adjustment or an air leak, debris or failure of an internal part, and stuck rings are likely causes. If running a dull chain got it really hot then you'll see evidence on the clutch side. It's possible to overheat the clutch side bearing and seal and damage them but that's rare.

Remove the muffler and the plug and turn the engine to where the top of the piston is at the top of the exhaust port, and then take some good pics of the piston skirt. Most seizures have the damage on the hotter exhaust side.

The ATF will help seal the rings when doing the compression test, giving a false high reading.

It is possible to seize the engine without it locking up. It's not really a seizure of course but the piston and often cylinder are damaged just the same. Or sometimes it will lock up and then free itself moments later, still damaged.