Seized chainsaw

[gstrom99]

OUCH. That's one tore up piston! The local Casey's sells non-ethanol gas also. Even though Husq says it can use "up to" 10% ethanol, I always buy the straight stuff, before mixing in oil and stabilizer, for my 2 stroke tools. I have plenty of gas cans around here - I just wish they came with decent (old style) spouts. The pre-mixed stuff is a good, but pricey, option too.

 

[ericm979]

That's quite a seizure.

Can we get a pic of the piston crown from the top, and from underneath (the inside of the piston, focused on the underside of the crown)? From the one pic it looks like it overheated, maybe caused by detonation. The missing piece of piston was melted away. That's likely detonation. By then the ring was already stuck in the groove and wasn't sealing. Once the piston melted the ring broke. The damage on the skirt is from lack of lubrication.

It's hard to say if the overheating was caused by detonation or caused it, and if the lack of lube on the skirt contributed to overheating or was caused by it.

Based on this I'd be wanting to check that there wasn't something causing it to run lean and hot, like an air leak or fuel blockage or a really bad carburetor setting.

 

[Snobdds]

OP never claimed straight gas.

Correct. That honor lies on me.

 

[RandyT]

OP never claimed straight gas.

I mistook the post number 2 for the OP which was a mistake

 

[RandyT]

View attachment 735762View attachment 735763

I am assuming that is the exhaust port in the cylinder in the picture and not the intake port. The problem is either that is the intake port and the saw ingested a foreign object or the piston was installed backwards at the factory. That piston damage is were the anti-rotation pin would be located which should be installed toward the intake port and would set between the intake port and the transfer port in the cylinder.

 

[Snobdds]

 

[MossRoad]

I am assuming that is the exhaust port in the cylinder in the picture and not the intake port. The problem is either that is the intake port and the saw ingested a foreign object or the piston was installed backwards at the factory. That piston damage is were the anti-rotation pin would be located which should be installed toward the intake port and would set between the intake port and the transfer port in the cylinder.

I'd guess the port you can see on the bottom of the picture is the intake port. The exhaust should have the studs on it facing towards the top of the picture. You can't see the exhaust port in that picture.

 

[RandyT]

I'd guess the port you can see on the bottom of the picture is the intake port. The exhaust should have the studs on it facing towards the top of the picture. You can't see the exhaust port in that picture.

Would be nice to also see the exhaust port to see which side the problem started on. Did the exhaust score first and the limited space drive the piston into the intake side of the cylinder or did the engine eat something and jammed between the piston and cylinder wall causing that damaged area on the piston.

 

[MossRoad]

Here's a pretty good video that shows several causes of scoring. The examples he shows all lean towards raw gas (no or not enough oil). Intake side is scored heavily. I'd like to see the other side of the piston.

Interestingly, around 11:00 he talks about the cold seizure we talked about earlier. Not warming the engine before going full throttle. Not the cause in this case, but a cause of piston scoring nonetheless.

 

[MossRoad]

Would be nice to also see the exhaust port to see which side the problem started on. Did the exhaust score first and the limited space drive the piston into the intake side of the cylinder or did the engine eat something and jammed between the piston and cylinder wall causing that damaged area on the piston.

I'm guessing he showed us the major damage side. Intake side of the piston and intake side of the cylinder. I'm sticking with raw gas, not enough oil in the mix, or some catastrophic debris injection.

But yes, it would be fun and educational to see the other sides.