Reason for this seizure

[Dan Forsh]

I've fixed the saw that this came out of for my brother in law, but I'm interested to know what the likely cause of the seizure was.

He wasn't sure if there had been oil in the fuel, but I don't see this being from a lack of oil.

The top ring has obviously broken and caused the piston damage, but I wonder was this the cause or effect?

Do rings just sometimes break or is there always a reason?

Anything tell tale you can see in the photos?

 

[Lakeside53]

I'd say "effect". Rings don't usually break for no reason - they just wear out.

Did the saw eat something?

 

[Dan Forsh]

It's a TS 400 so it could have.

Piston looks great other than the obvious. No notable wear on the wall thickness on the intake side, no scoring or abrasion either.

So what might it have likely eaten do you think?

Could this happen if the ring got stuck?

 

[Tzed250]

looks like FOD to me

 

[Lakeside53]

It's possibe, but not that common. That piston looks pretty normal to me (other that the damage).

 

[Dan Forsh]

Okay, so that's one I haven't come across before.

FOD would be?

 

[Lakeside53]

Foreign Object Damage

 

[Dan Forsh]

Foreign Object Damage, thanks, I'll remember that one.

All the filters were in place so I can assume something through the muffler then. The plug and decomp valve weren't missing anything.

Maybe a chunk of carbon falling back through the exhaust port? Would this be hard enough?

 

[doc874]

piston/ring damage

Has some work been done on this saw like piston/rings replaced or is this the original factory installed piston? If the piston was replaced after factory or rings installed, than, it may be that the top ring was installed upside down making the ring sit-out just enough to catch the exhaust/intake port. I have seen this before but not quite to the extent of yours. Check cylinder ports for nicks or damage as well.


Doc

 

[PES+]

Piston installed backwards or wrong piston in wrong cylinder.
Ring got caught in port and snapped

 

[Steve128]

Fod

Would the FOD cause the other bright marks on top of the piston?

 

[Stihldoc]

I'd like to see another view of the top of the piston with a notation of what direction faced the exhaust port. What saw did this come from? What octane fuel was used, was ethanol in the fuel? I've seen lots of detonation-caused failures where the upper edge of the piston facing the exhaust port has been blasted away, resulting in upper ring failure. Detonation is an often-overlooked cause of failure because it is so easy to miss the damage to the top of the piston when so much other resultant damage exists. You can't hear detonation (octane knock) in a saw because of all the exhaust noise, but it is often there. Its like some medical condition that can only be discovered by autopsy. I can't tell from these pictures if detonation was a factor in this failure. FOD is an easy one to diagnose- look at the intake side of the piston- especially the lower skirt- any FOD entering the crankcase has to get by the piston FIRST. The one notable exception to this statement is the failure of a decompression valve- it is already in the combustion chamber. Failure analysis is fun, provided its not your saw.

 

[Dan Forsh]

I think PEST has it figured.

I cleaned the top of the piston up to find the little arrow, but it was really feint and I wasn't 100% it wasn't just another mark from the rings.

The piston is Gen Stihl and I have another for the same model, so I looked at the new one for comparison.

Sorry, my close up photography isn't the best.

You can see the deep gouge in the cylinder just above the exhaust port caused by the ring.

In the second pic I've cleaned the piston head up enough the see the AB and what I think is the arrow. I've orientated the piston exactly as the new one next to it. If the arrow is supposed to point to the exhaust port and the damage to the piston edge matches the damage inside the cylinder, I'd say that the piston was in the wrong way round as PEST suggests.

CASE CLOSED thanks to everone for the input.

Dan

 

[Sprig]

Wow!

Great leaning curve thread gents and a good call there Pest! So, small dumb Q here, I can see the piston is toast but is the jug salvagable with that much damge? Or would cleaning it up and re-using it lead to another catastrophic failure of another sort? :monkey:

 

[RiverRat2]

Agree with the Pest on this one, looking @ the piston the ring pin post are clearly visible on the damged side which coincides with the cylinder damage over the exhaust port,,,, Ive always seen the those Pins on the intake port side of the piston,,, Good call Pest

 

[RiverRat2]

Great leaning curve thread gents and a good call there Pest! So, small dumb Q here, I can see the piston is toast but is the jug salvagable with that much damge? Or would cleaning it up and re-using it lead to another catastrophic failure of another sort? :monkey:

Toast!!!!!!!!

 

[Steve128]

Pest

 

[PES+]

Please don't do that

Bow before no man nor institution....
I am but a man.....who likely should have been institutionalized years ago

 

[oldsaw]

Bow before no man nor institution....
I am but a man.....who likely should have been institutionalized years ago

Are you looking for someone to disagree with that comment....here of all places...you are certifiably institutional material...:biggrinbounce2:

Mark

 

[rahtreelimbs]

Bow before no man nor institution....
I am but a man.....who likely should have been institutionalized years ago

Don't need to bow just bend over.............lets have some fun!!!




Institutionalized.............ya think!!!