Broken piston crown (Echo CS-7310p)

[EFSM]

What is the reason for a piston crown breakage? I've been scratching my head over this one--there is no sign of scoring, plenty of lubrication, and no damage to the rings or cylinder whatsoever. This is a high use saw but only 14 months old. The ring side clearance was only 0.005". It has had Red Armor in it all its life and these have one of the best air filters on any saw ever. I suppose this is a case of a manufacturing defect, but it seems it should show up before hundreds and hundreds of hours.

 

[Nutball]

I doubt over-revving causes extreme heat, but it sure causes a lot of stress. The plating can wear thin too after a lot of use, and the rings get sharp and are more likely to catch the port.

 

[Wilhelm]

I would think ring groove/land too wide.
Either a manufacturing tolerance mishap or wear & tear.
Ring slapped up & down in the ring land till the piston crown fatigued & broke.

Just a morning brainfart , I didn't even had my coffee yet so take it for what it is - just a thought.

 

[Motorka]

Ported ?

 

[drf256]

That’s a tight ring gap. Is that typical? I’ve never been in the model.

Has the saw been modded at all? Was it run lean? The bottom end looks nice and wet for sure.

Kinda looks like maybe some detonation. Then heat causing ring to swell and likely catch the exhaust port floor multiple times. Would continually tap the crown upwards until it busted.

Any jug pics?

 

[Wilhelm]

Are both ring locating pins still in there?
Any chance the top ring rotated and got caught in a port?

 

[Wilhelm]

...
Any jug pics?

Pervert!

Although, how about some air filter pics.

 

[EFSM]

Ported ?

Not when it failed. It will be when it leaves.

Are both ring locating pins still in there?
Any chance the top ring rotated and got caught in a port?

Yes. I had that in another 7310, but the rings on this are immaculate.

I would think ring groove/land too wide.

Echo specs .004 to .006. These were .005.

Was it run lean?

It had a hole in the fuel line a couple of weeks before this episode. However there are no signs of lean damage; but this is a KANIBORON® coated piston, which may mask signs of lean running.

Any jug pics?

Yes, quite literally.

 

[EFSM]

Pervert!

Although, how about some air filter pics.

Hawk tuah!

 

[mainer_in_ak]

Half a million ports in saws nowadays. I bet occasionally ring/piston crown issues can happen.

I own alot of echo power equipment but I've never warmed up to the 7310. A $grand for a Chinese carb and a rev limited coil. No thanks.

Though the 7310 replaced the cs 800p, it sure as heck hasn't replaced my brick sht house cs 8000.

 

[EFSM]

A $grand for a Chinese carb and a rev limited coil. No thanks.

I don't like Zama carbs either, but the C3's like they use are really good carbs overall. And the coil is not rev limited as far as I know. Once ported, they will really scoot. But no, they can't shed 4 pounds without becoming less brick house-ish.

 

[jacob j.]

Echo specs .004 to .006. These were .005.

That's common with Japanese engineering. They like close tolerances and then expect the end user to know what they're doing.

If you go inside some of the older Echos and Shindaiwas, they really had good engineering in them from the early days, even
though the older saws were tuned to run much lower RPM curves.

 

[drf256]

Not when it failed. It will be when it leaves.

Yes. I had that in another 7310, but the rings on this are immaculate.

View attachment 425920View attachment 425921

Echo specs .004 to .006. These were .005.

It had a hole in the fuel line a couple of weeks before this episode. However there are no signs of lean damage; but this is a KANIBORON® coated piston, which may mask signs of lean running.

Yes, quite literally.

View attachment 425922

That’s a nice cylinder design. Ports kinda big though.

 

[smokey7]

I would say that ring is tight or it has a side clearance issue. When it had the fuel line issue it could've cracked it if it butted rings then just finished it off after. .005 is tight to me for that bore size sure not much room for oops the fins got a little dirty. Or a batch of not so fresh gas.

 

[huskihl]

What does “ring side clearance“ mean? Are you saying that the end gap was only .005”?

For what it’s worth, if the gap was too tight, the rings expand into the exhaust port and will catch the plating and strip some off the plating off the center of the exhaust port. I’ve done it. If there’s no damage to the cylinder above or below the exhaust port, I would blame this on over revving

 

[smokey7]

Side clearance is the gap the ring has in the groove aka top and bottom. I don't know a number but I'm sure there is a spec involved

 

[huskihl]

Side clearance is the gap the ring has in the groove aka top and bottom. I don't know a number but I'm sure there is a spec involved

if that’s the case .005 is pretty excessive. Usually the grooves are about .001– .002“ wider than what the ring is just for oil clearance

 

[smokey7]

I agree. I was was confused with the term side gap... Most just measure end gap and to me .005 seems tight for that bore size with a cast ring. And your guess of .001 .002 seems reasonable I don't know what it should be but giving it a running start to beging hammering the land out it could get loose enough to damage a piston top I guess. But on a saw 14 months old seems little low hour unless a landing saw or something.

 

[EFSM]

005 is tight to me for that bore size sure not much room for oops

Side clearance is the gap the ring has in the groove aka top and bottom.

I agree. I was was confused with the term side gap

The end gap is .017.

if that’s the case .005 is pretty excessive. Usually the grooves are about .001– .002“ wider than what the ring is just for oil clearance

Echo specs, as I said, are .004-.006. I measured the side clearance again and found it varies substantially, from less than .003 on the bottom ring to about .007 beside the broken section. I apparently should have measured at more than one spot. I'm wondering if the piston got hot enough to deform on the exhaust side, because I'm sure it couldn't have worn that bad. This engine never ingested dirt.