What caused this failure?

[wanab]

the wrist pin and spark plug tell the story here. if it was cold seized the pin would still be lubed. even if the saw was run lean your still getting 50:1 @ the pin.

there was a cataclysmic event here.

 

[Madsaw]

I have never had a chance to see acold seized piston yet. But from my understanding of motors and such . I would say this was a cold siezed. Why might you ask. Just so much scorreing all around the piston expect on the intake side. The intake side would be cooled by the next charge coming in. The first pics Brad posted was all wiped down. But the later pics showed everything well oiled. Then here is the real tell. The guy owns other saws adn they did not seize. So if it was the mix or he likes to lean them out more. He would have more then just one fried saw.
Brad you said this is the second time this happened to this saw? If so the cylinder could have been a bit tight. I have seen a few tractor locked up from a freash rebuild from to tight of tolernces if they are brought up to temp to fast.
Later
Bob

 

[blsnelling]

LIke you just mentioned this was the second piston he seized. He admitted that the first happened the exact same way. Pulled it off the trailer cold and droppedit straight in a big log with an extended full load cut with 0 warm up time. Only I will admit that I questioned how tight the first piston was. That was the one I ordered from Greece and I questioned it. That's why I replaced it free of charge with another new Golf piston. The Golf piston fit properly.

A cold seize is the only explanation that fits.

1. His other saws were running the same gas
2. The saw had already seen about 10 tanks of gas and ran perfectly when it was put up the day before.
3. The plug was colored rich if anything.
4. I tuned the saw to less than the factory spec of 12,000.

 

[Nailgunner]

Well handled there. Minimum outlay, a little work, no opportunities for future hassles, and you may have actually made the guy wiser and less of an encumberance to others. Patience pays off

 

[Jacob J.]

Brad- you done good. It takes a lot of patience to keep fixing a machine when someone else has screwed it up due to negligence or just plain ignorance.

 

[icelation8]

If that was a new piston it sure has a lot of carbon build up for being test run and then run one time after that. Also it looks like on the intake side of the piston the machine marks are wore off the rings already and the intake side of the piston skirt sure doesn't have much for machine marks either. Machine marks take hours to wear out not a couple of starts.

Straight gas would show scoring on the intake side as well as the exhaust. metal on metal would give you the same results on both sides of the piston.

I would be leaning towards cold seize or carbon scoring.

 

[blsnelling]

I believe what you're calling carbon buildup is actually deposits of aluminum when in the molten state.

I don't believe the Golf rings have the machine marks like Stihl rings do.

I did notice that the machine lines are gone from the piston as well.

 

[icelation8]

Even the carbon on top of the piston that looks like it has more time on it than one use just my oppinion.

Carbon scoring is when the carbon builds up on top of the piston or the in the exhaust port and starts to flake off or break down. It mixes with the oil that is on the piston and you have basically a grinding compound between the cylinder and the piston.

 

[blsnelling]

I did'nt say one use. It had about 10 tanks of fuel through it. That's still not much time to build up carbon though.

 

[PES+]

Brad

Do you still have the other piston that got trashed?

Also can you post a pic of the rod from inside with this piston installed? You do not need the pin in it.....I just would like to see the space between the rod and the pin bosses.

This piston looks like it starved only the small end bearing and the pics show that the piston expanded/deformed at the pin.

I have seen some pistons that do not have the proper cut outs and or oil holes drilled and this can result in a failure very much like this one.

If you do not have the other Greek piston can you remember if it failed in a near identical way or did it look different?

 

[blsnelling]

The pictures on this page are of the previous piston. The damage was different in a few ways. The scoring did not wrap as far around the piston. It actually had less damage. There was more aluminum tranferred above the exhaust port, instead of below. The wrist pin was not heated that time. LINK. I can't get any more pics of it since it's put back together.

 

[blsnelling]

They say confession's good for the soul? Well here goes. I hope someone benefits from this. I know I learned a lesson or two.

My latest repair on this saw came back after only about an hour of use. It never siezed up, but wouldn't start. Compression was down to 120. OK, it's time to get to the bottom of this. I totally disassembled the saw, leaving only the cylinder. I bolted the muffler back on with a piece of inner tube under it. I clamped a piece on the intake as well. I then hooked my vacuum pump to the impulse line. It was slowly leaking. I sprayed carb cleaner on the flywheel side crank seal. No change. I then sprayed it on the clutch side seal and it sucked the liquid right in. Now that the oil was gone off the seal I really had a vacuum leak. So both seals came out and new ones are going in both sides.

Now. How can a saw idle properly and seemingly hold a tune in the shop yet have a vacuum leak that significant? I have erroneously operated on the principle that if there's a vacuum leak, the saw won't run as well as this saw did. I had a much less severe seal leak on a 026 and it wouldn't idle down properly.

As I've read so often here, if your saw scores a piston, find out why or it's apt to do it again. Now I get to eat crow and make this right for the guy. They guy still doesn't know how to operate or maintain a chainsaw and might be a jerk at times, but it looks like lack of attention to detail was the cause of these piston seizures.

I hope someone gets something out of this and that I still have atleast a little bit of a reputation left

 

[belgian]

They say confession's good for the soul? Well here goes. I hope someone benefits from this. I know I learned a lesson or two.

My latest repair on this saw came back after only about an hour of use. It never siezed up, but wouldn't start. Compression was down to 120. OK, it's time to get to the bottom of this. I totally disassembled the saw, leaving only the cylinder. I bolted the muffler back on with a piece of inner tube under it. I clamped a piece on the intake as well. I then hooked my vacuum pump to the impulse line. It was slowly leaking. I sprayed carb cleaner on the flywheel side crank seal. No change. I then sprayed it on the clutch side seal and it sucked the liquid right in. Now that the oil was gone off the seal I really had a vacuum leak. So both seals came out and new ones are going in both sides.

Now. How can a saw idle properly and seemingly hold a tune in the shop yet have a vacuum leak that significant? I have erroneously operated on the principle that if there's a vacuum leak, the saw won't run as well as this saw did. I had a much less severe seal leak on a 026 and it wouldn't idle down properly.

:

If you had a significant leak as mentioned, I suppose you have been compensating a lot on the L screw (richer) for idle. That could have pointed out the problem ....
anyway we all learn the hard way ; it's called experience !!!

opcorn:

 

[blsnelling]

If you had a significant leak as mentioned, I suppose you have been compensating a lot on the L screw (richer) for idle. That could have pointed out the problem ....

opcorn:

Not at all. 1 1/8 turns. Idled perfectly. That's how I found the leak on my 260. I couldn't tune it to idle properly. It just wanted to race.

 

[belgian]

Not at all. 1 1/8 turns. Idled perfectly. That's how I found the leak on my 260. I couldn't tune it to idle properly. It just wanted to race.

My jonny 49sp had the same behavior/problem. Idles fine but once you turn it on its side, it dies quickly.

It still worries me though that the air leak on your saw was not noticeable in any way in the first place.

 

[blsnelling]

It still worries me though that the air leak on your saw was not noticeable in any way in the first place.

Worries me to. Now I feel like I have to go to the trouble to leak test every saw I work on.

 

[Lakeside53]

Simple.... 'cos I had to figure that out a few times before...

The carb on the 056/45 will gravity feed.... one of the few... which is also why they start so well.

Big engines are less affected by leaks at idle than small... Obviously the seal sucked a lot more air at higher rpm.

 

[Lakeside53]

Worries me to. Now I feel like I have to go to the trouble to leak test every saw I work on.

If you do anything major, or can't find a definitive cause,

YES



It only takes few minutes once you done a few, and not only finds the bad stuff, but saves a bunch of time as you don't down the rat holes of wrong parts. I.e. prove the basic engine, then it can only be carb or ignition...

 

[mtngun]

I hope someone gets something out of this and that I still have atleast a little bit of a reputation left

I admire a man who is big enough to admit he made a mistake and learn something from it so he doesn't make the mistake again.

Let me see if I can rep you.

 

[mtgrs737]

Looks like your typical no/too little oil damage to me. The engine ran until the drain down oil was washed out of the crankcase and the carb then came the raw gas from the morning fill up and ouch! What a shame. This type of thing happens all the time, but most folks don't try to cover it up by dumping in a bottle of oil in the tank. We are all human, this type of mistake can happen to any of us.