Broken piston crown (Echo CS-7310p)

[Woodtroll]

It seems that fellow is kind of rough on saws. Some folks can break anything.

 

[bwalker]

Same customer, different saw (620 instead of 7310). This is the 3rd time this saw has had this exact failure, which I blame on overspeeding. I put a 590 single ring piston in it so hopefully the ring lands are stronger.
Lots of oil, but the piston got toasty at some point.
View attachment 482615View attachment 482616View attachment 482617

Ring gap too tight. Piston appears not to be ran too hot or it would show "death ash" beneath the crown, which it doesnt have.

 

[legdelimber]

I've seen some Echo blowers pb-403 pb-413 and pb-620's , that the exhaust port was nearly flat on top. High hour landscaper units. Machine marks worn off of the pistons and the cylinder plating looking thin in places, in the couple that I pulled the cylinder.
At idle, the rings sounded like a spoon player.
I was truly surprised that the pistons tops or rings hadn't been broken on the exhaust port.
Guy said that he had never run anything but Echo Power Blend oil in them.
No idea of the ratio.
Edit: the looks of things would make me think the ratio was no heavier than 40:1 on the oil.

 

[EFSM]

Ring gap too tight. Piston appears not to be ran too hot or it would show "death ash" beneath the crown, which it doesnt have.

There is no scoring, which should happen during a case of the ring being tight. Also, a tight ring gap would show up before a year of hard use. I actually don’t even bother checking the ring gap on Echo pistons anymore because I haven’t ever found one that needed adjustment.

 

[bwalker]

There is no scoring, which should happen during a case of the ring being tight. Also, a tight ring gap would show up before a year of hard use. I actually don’t even bother checking the ring gap on Echo pistons anymore because I haven’t ever found one that needed

Scoring often doesn't accompany this situation.
And it can go along time before manifesting itself. All it takes is a heat excursion, the rings expand, rings gaps close and boom.

 

[EFSM]

Scoring often doesn't accompany this situation.
And it can go along time before manifesting itself. All it takes is a heat excursion, the rings expand, rings gaps close and boom.

I’ll measure the gap later this week.

 

[bwalker]

I’ll measure the gap later this week.

Also inspect the exhaust port roof for any damage.

 

[EFSM]

Also inspect the exhaust port roof for any damage.

The cylinder and roof are perfectly fine. Other than the plating getting thin beside the port where the loose piece of aluminum was bouncing around.

 

[bogieboy]

Out of curiousity, whats the piston to cylinder clearance? That slug looks aweful worn, as i dont see any mavhining marks left on it... which can cause piston rock, and added stresses to all the piston surfaces....

 

[EFSM]

Out of curiousity, whats the piston to cylinder clearance? That slug looks aweful worn, as i dont see any mavhining marks left on it... which can cause piston rock, and added stresses to all the piston surfaces....

I didn’t measure, but it wasn’t too bad. The worst cases I have seen are concrete saws (where the skirt can wear through) and a pair of 562’s that had such worn skirts they no longer ran due to low crankcase compression.

 

[Reloaderguy]

Top ring put on up side down?

 

[EFSM]

Top ring put on up side down?

No, the 620s have an offset pin so there’s no way to do that. The 7310’s have an enclosed pin so there’s is no up on the rings.