Chainsaw cause of death?

[oldlawnguy]

Gentlemen,

Any insight on cause of this catastrophic piston failure? (pictures attached)

Cylinder looks well lubed. I did noticed on disassembly the grommet c-clamp (came loose) was not attached to large diameter part of grommet that attaches to cylinder and seals with c-clamp.

Pretty ugly scoring.

The failure occurred while the chainsaw was doing a horizontal leveling (saw sideways, bar level to ground) cut of a large tree. It was humming along and literally just stopped like I killed the switch. I let it cool a bit, and it almost started a few times until it seized up.

Does not look like it was running lean, if anything with the oil in cylinder looks a little fat. Cylinder has minor scoring only beneath the intake.

Scratching head

Thanks

 

[mechanic mark]

What brand & model chainsaw? Have you been using OEM 2 cycle oil recommended by manual?

Replace oil pump along with failed parts.

 

[StarTech]

Kinda looks like it inhaled a screw or other forgien hard object. Also check for bearing failure.

 

[ILENGINE]

No question that was foreign object ingestion.

 

[bertsmobile1]

For the benefit of you understanding how to diagnose the failure as Star & Ilengine have diagnosed correctly .

All of the damage is on the bottom of the piston and not on the top.
That indicates something got into the engine that was too big or heavy to pass from the crank case through the transfer ports & into the combustion chamber
Further more all of the damage is on the induction ( carb side ) so that confirms a foreign object .
The gouges are deep & sharp so it has to be some thing metallic, like a screw from the carb butterfly or a lump of gravel.
The piston is complete with no horrizontal cracks , deformation or scuffing so that rules out a bearing failure or bearing break up
There is almost no damage to the crankcase but the image is too small to properly inspect it .
What caused the damage should still be in the crankcase or even under the piston.
The other thing that causes damage like this is a piston pin clip falling out but usually that shows some gouges on the side before it drops into the crankcase and you usually find it chewed up in the case plus the piston can then shift sideways so you get scuffing on the side of the piston .
You could not discount this as the saw was running fine till you tipped it sideways

Back in the old days manifolds used to bolt onto the cylinder and owners used to get the screws mixed up so you could insert a spring that was too long and broke through the cylinder.

 

[Hammermechanicman]

Definitely sucked in some junk.



It'll probably buff out?

 

[oldlawnguy]

For the benefit of you understanding how to diagnose the failure as Star & Ilengine have diagnosed correctly .

All of the damage is on the bottom of the piston and not on the top.
That indicates something got into the engine that was too big or heavy to pass from the crank case through the transfer ports & into the combustion chamber
Further more all of the damage is on the induction ( carb side ) so that confirms a foreign object .
The gouges are deep & sharp so it has to be some thing metallic, like a screw from the carb butterfly or a lump of gravel.
The piston is complete with no horrizontal cracks , deformation or scuffing so that rules out a bearing failure or bearing break up
There is almost no damage to the crankcase but the image is too small to properly inspect it .
What caused the damage should still be in the crankcase or even under the piston.
The other thing that causes damage like this is a piston pin clip falling out but usually that shows some gouges on the side before it drops into the crankcase and you usually find it chewed up in the case plus the piston can then shift sideways so you get scuffing on the side of the piston .
You could not discount this as the saw was running fine till you tipped it sideways

Back in the old days manifolds used to bolt onto the cylinder and owners used to get the screws mixed up so you could insert a spring that was too long and broke through the cylinder.

Thanks all. You nailed it! On further inspection its missing the piston retaining ring (~$1 part). You can see small blobs of molten steel in cylinder, but I cannot find any pieces of ring (even looked in muffler). It turned over a few times after I let it cool down so could it have ejected what was left? Saw was working great for an hour cutting up big tree.

Given the cylinder scoringe (see attached) is below the intake can I buff it out and give it a go with a new piston, ring and retainers?

I'm not a pro so would rubbing out with #0000 steel wool be an option or should I try something else?

Thanks!

Thanks

 

[bertsmobile1]

We have all been there before
And the simple answer is no
The piston & cylinder are toast
You can get reasonable quality cylinder & piston kits from Huztl direct from China or buy much more expensive kits locally.
If buying from China you will need to know the Husqvarna equivalent model number and check the images carefully to make sure the carb mountings are the same .
If you are lucky then there will be a bigger bore kit that will fit because they are only a couple of dollars dearer than the standard size so end up with a horse or two more grunt.
Avoid anything on evilbay or ammo zone as that are a lucky dip as to the quality some are good & others are stuff the vendor bought as scrap metal because they failed quality control
I usually replace the bearings just in case the debris bouncing around inside damaged the oil seals
You don't want to spend 3 hours rebuilding the saw only to find the crank leaks .

 

[slomo]

I always shake/swirl the fuel jug up nicely prior to filling any 2 smoker tank.

Seen numerous boats where the guys would dump a bottle or two of oil in
the tank. All that oil settles to the bottom. Must be a foot of oil down there. Oil never gets mixed up.

slomo

 

[oldlawnguy]

We have all been there before
And the simple answer is no
The piston & cylinder are toast
You can get reasonable quality cylinder & piston kits from Huztl direct from China or buy much more expensive kits locally.
If buying from China you will need to know the Husqvarna equivalent model number and check the images carefully to make sure the carb mountings are the same .
If you are lucky then there will be a bigger bore kit that will fit because they are only a couple of dollars dearer than the standard size so end up with a horse or two more grunt.
Avoid anything on evilbay or ammo zone as that are a lucky dip as to the quality some are good & others are stuff the vendor bought as scrap metal because they failed quality control
I usually replace the bearings just in case the debris bouncing around inside damaged the oil seals
You don't want to spend 3 hours rebuilding the saw only to find the crank leaks .

I'll replace the cylinder as well. It's $57.25 from the local distributor I use up here in Boston. Cheaper than most other online parts places who have pretty high markup. I avoid the shipping $ and pick it up myself. Don't mind using local and paying more as they have taxes, employees, and quality control in their supply chain. Half the fun is rebuilding and the other half is getting it to work.

Yes HeeHeeBay is great for stuff you don't want to work and I only buy stuff on AmIGone that you can return. I have gotten decent stuff like fuel lines, bulbs and fuel filters there. Even found a $15 replacement carb for weedwacker, because I could not find carb kit on noname carb. I smile every time I open up a 2 cycle engine and see a Walbro carb. I get a $10 Walbro carb kit not those knockoff miss kits online.

Thanks again for helping and giving back with your knowledge and expertise to and old DYIer.