How's This Piston Looking?

[Campin' Cutter]

Pulled this piston out of my 262 I rebuilt a year or so ago. To my untrained eye it doesn't look too bad apart from some carbon on the exhaust side. I'd appreciate some feedback on the condition, so that I can learn more about what I should be looking for aside from the obvious like scoring. This was cleaned in my ultrasonic cleaner before pictures, which is why the piston head has some discoloration and no carbon. Thanks all!

 

[tomalophicon]

Looks scored to me but I guess if you're saying it's carbon it can be removed.

 

[Campin' Cutter]

Looks scored to me but I guess if you're saying it's carbon it can be removed.

If it's scored its very light, can't feel it at all with my fingers. The picture doesn't capture it well but in person those vertical lines on the exhaust side are black like carbon,so I assumed it was carbon based on appearance and not being able to feel any scoring. Could be wrong as I'm definitely no expert, that's why I'm asking. Thanks for the reply.

 

[Campin' Cutter]

The exhaust port had a fair amount of carbon build up before I cleaned it. It sort of looks to me like maybe a chunk of carbon let go and scored the exhaust side.

 

[Bob Hedgecutter]

Dunno- that second photo to me looks like there has been transfer of piston material to cylinder wall, that melty hotty smeary effect..... hard to tell after you cleaned it up, but I also agree there looks to be some carbon scores exactly where the exhaust port might be, ones that you should be able to "feel" with a fingernail or fine pick.
Photos of the uncleaned corresponding cylinder might give more of a hint, but at this stage I would suggest you have been lucky not to pinch the ring in the lands.
You can take the ring out, lightly sand the piston, check for burrs on the land edges and after decarboning the exhaust- slap it all back together and then have the saw tuned by someone that can set it correctly and think about your mix strength.

 

[tomalophicon]

I'd give that side of the piston a very light sand and see where you end up.

 

[MacAttack]

It's a long way from being "bad" but it looks like some scoring and scuffing on the exhaust side, if that were my saw I would be very intently checking my fuel / air adjustments on the carb. I personally don't know if it's from carbon, I've had plenty of saws with a lot of carbon buildup but the piston still looks shiny.
This isn't a great picture, but this is a 60 year old saw that had so much carbon I could have used a shovel to scoop it out. (Saw was originally run on 16:1 motor oil). Some very light marks on exhaust side and that was it.

 

[Campin' Cutter]

Dunno- that second photo to me looks like there has been transfer of piston material to cylinder wall, that melty hotty smeary effect..... hard to tell after you cleaned it up, but I also agree there looks to be some carbon scores exactly where the exhaust port might be, ones that you should be able to "feel" with a fingernail or fine pick.
Photos of the uncleaned corresponding cylinder might give more of a hint, but at this stage I would suggest you have been lucky not to pinch the ring in the lands.
You can take the ring out, lightly sand the piston, check for burrs on the land edges and after decarboning the exhaust- slap it all back together and then have the saw tuned by someone that can set it correctly and think about your mix strength

This saw came to me rode hard and put up wet, hence why I rebuilt it. Here are some pictures of the cylinder and piston before cleaning. Unfortunately I don't have any of the exhaust side of the piston except through the exhaust port. The saw has been fully cleaned and rebuilt, cylinder cleaned up fine (don't recall any melted/transferred piston but could be wrong) and a new piston was installed. Saw has been tuned properly with a tachometer and reads 170 on my echo compression tester. I was more curious about the general condition of the piston, as the saw itself was rough when I got it. It required quite a bit of work to clean it up and repair everything.

 

[Campin' Cutter]

To clarify, I bought this saw and immediately rebuilt it. It's history is unknown. It's sounding like maybe a mix of carbon scoring and carb being a little lean? I could certainly buy that given how rough the saw was overall

 

[Campin' Cutter]

It's a long way from being "bad" but it looks like some scoring and scuffing on the exhaust side, if that were my saw I would be very intently checking my fuel / air adjustments on the carb. I personally don't know if it's from carbon, I've had plenty of saws with a lot of carbon buildup but the piston still looks shiny.
This isn't a great picture, but this is a 60 year old saw that had so much carbon I could have used a shovel to scoop it out. (Saw was originally run on 16:1 motor oil). Some very light marks on exhaust side and that was it.

Thanks Mac Attack! It's been tuned properly with a tach since I bought it and rebuild it , then richened up just a hair.

 

[820wards]

Looks scored to me but I guess if you're saying it's carbon it can be removed.

Skirt scoring is usually caused by carbon buildup on the piston top and a dirty or no air filter. Carbon buildup is also caused by incomplete air-fuel combustion. I have changed all my spark plugs to E3 plugs. The E3 plugs do the best at complete air-fuel burning I have found testing race engines on dyno’s.
j-

 

[jfn2]

If you look at the 2nd pic and blow it up you see what looks like some detonation at the timing edge and then look at the 3rd pic and blow it up and look real hard at the piston edge you'll see some deto. Then look at the top left side in the 3rd pic and something was eating at the alum. Not good!
jfn2

 

[Campin' Cutter]

Skirt scoring is usually caused by carbon buildup on the piston top and a dirty or no air filter. Carbon buildup is also caused by incomplete air-fuel combustion. I have changed all my spark plugs to E3 plugs. The E3 plugs do the best at complete air-fuel burning I have found testing race engines on dyno’s.
j-

As you can see in the pictures the piston head had very little carbon on it. I don't doubt that whoever owned it before me ran it regularly with a dirty air filter, as the entire saw was caked with sawdust mixed with oil. Stripped screws everywhere, etc. Previous owner apparently never heard of maintenance, but I got her cheap as a project so I didn't mind.

 

[Campin' Cutter]

If you look at the 2nd pic and blow it up you see what looks like some detonation at the timing edge and then look at the 3rd pic and blow it up and look real hard at the piston edge you'll see some deto. Then look at the top left side in the 3rd pic and something was eating at the alum. Not good!
jfn2

So what causes detonation?

If you look at the 2nd pic and blow it up you see what looks like some detonation at the timing edge and then look at the 3rd pic and blow it up and look real hard at the piston edge you'll see some deto. Then look at the top left side in the 3rd pic and something was eating at the alum. Not good!
jfn2

The only thing I know about detonation is that it's caused by low quality/low octane fuel or incorrect ignition timing. Having replaced the piston, cleaned up the cylinder, and cleaning/restoring the rest of the saw and always running ethanol free 91 since the rebuild, I'm not too worried about detonation problems. Also, it's very possible what "ate" the piston a bit is the ultrasonic cleaner. I've heard that the cavitation they cause can eat through aluminum.

 

[ITLHAPN]

Amsoil Saber 100 mixed 40:1, 93 octane. 12 years, loaned to a novice, pegged not in the wood, crud in the carb needle. 2008 346xp, used muriatic acid to remove the Aluminum from the cylinder, put a new piston, ring and ported the cylinder when going back together.
If you look you can see the machining marks from the original manufacturing.

 

[MacAttack]

In the past I have had detonation / pinging / pre-ignition in a 2-stroke that was jetted lean and had a sparkplug that was too hot of a heat range. I installed a larger main jet and a cooler plug and it went away. It was a dirtbike but same principle.
I understand tuning with a tach is a more high-tech method, but I've never gone wrong tuning by ear with a healthy amount of 4-stroking wide-open without a load on the saw.

 

[Campin' Cutter]

Amsoil Saber 100 mixed 40:1, 93 octane. 12 years, loaned to a novice, pegged not in the wood, crud in the carb needle. 2008 346xp, used muriatic acid to remove the Aluminum from the cylinder, put a new piston, ring and ported the cylinder when going back together.
If you look you can see the machining marks from the original manufacturing.

That last picture of the piston . This is why I never loan out my saws when my buddies ask! I just go with them and do the cutting, gives me a reason to play with my saws

 

[Campin' Cutter]

Mac Attack,

Thanks for the tips. I've only recently joined a few months ago but I've been lurking on this site for years. I've read a lot of posts you've made and have learned quite a bit from you, so thanks. As far as tuning with a tac or by ear, I do both. For example, I recently picked up a 288xp and just tuned it with my tach last weekend to a few hundred Rpms under the listed max. Tried to cut some small mesquite and it was bogging like crazy! Richened her up just a hair and I then understood why people like 288s! I guess what I'm saying is that I use the tach to get close, then adjust by ear and performance.

 

[leeha]

Not sure what saw your working on but if a new piston is available i would replace it.
It has a lot of wear on the skirts not to mention the light scoring. If the saw is an occasional
user you could get by with it.

 

[Campin' Cutter]

Not sure what saw your working on but if a new piston is available i would replace it.
It has a lot of wear on the skirts not to mention the light scoring. If the saw is an occasional
user you could get by with it.

Yeah see the other posts, piston has already been replaced. I was more seeking input on the condition for my own learning, so thanks. I had definitely noticed the skirt wear