Carbon build up on exhaust side of piston. Bad?

[ANewSawyer]

Sorry, this was the best picture I could get. My camera did NOT want to focus that deep.


As you can see, there seems to be quite a bit of carbon built up below the rings. Is this bad? I know there is also carbon on the top of the piston.

 

[Nitroman]

How well is your saw tuned? What mix (oh God, not another oil thread), are you running?

 

[ANewSawyer]

This is a completely new to me engine. I am refurbishing it. I don't know what oil was used in it before. I was mainly worried that a ring might be stuck. It is a Shindaiwa T-25 weedeater. (<Yes, the same weedeater I have been working on.)

I have heard that Stihl Ultra is good to dissolve carbon if is loose. I have been planning to run Lucas semi-synthetic 2 cycle oil in it, though.

 

[treesmith]

Isn't carbon below the rings a sign of blow by? Might be time for new rings, hows the compression?

 

[ANewSawyer]

I don't have a pressure tester. It runs fine though, for what little I have run it. The engine is oriented correctly in that photo. You can almost see the crown of the piston. There isn't any carbon on the rings, just between the upper and lower rings. And below the lower ring. Also, I don't see any carbon between the upper ring and the piston crown in the photo. That seems strange to me. The only thing I know about blow by it from this site: http://www.smellofdeath.com/lloydy/piston_diag_guide.htm And that site isn't even for chainsaws and weedeaters.

IDK, that is why I am asking you guys. Thanks for the help!

 

[CTYank]

One problem that can occur when using mix oil meant for water-cooled 2-strokes in air-cooled engines, is deposits forming in the ring grooves. Those deposits stick the rings, and don't let them seal as they should.

Then you get blow-by, just like it seems has happened.

Not a great idea to run a 2-stroke too rich, with too much oil, or too gently. Gets them off their feed, so to speak.

Short of a tear-down, I've no idea how to get that poo out of the ring grooves.

 

[fearofpavement]

Make up some good mix and run the thing. Run it hard, too many people baby a string trimmer. These engines don't do well at partial throttle settings. Run half a dozen tanks through it and see if it looks any better.

 

[ANewSawyer]

I am thinking I will use the Lucas oil at 32:1 and see what it looks like. Though maybe I should use Stihl ultra. Why do I feel like this is now an oil thread?

One problem that can occur when using mix oil meant for water-cooled 2-strokes in air-cooled engines, is deposits forming in the ring grooves. Those deposits stick the rings, and don't let them seal as they should.

Then you get blow-by, just like it seems has happened.

Not a great idea to run a 2-stroke too rich, with too much oil, or too gently. Gets them off their feed, so to speak.

Short of a tear-down, I've no idea how to get that poo out of the ring grooves.

It is obvious that his was not run hard enough by the previous owner. I hope to remedy that situation!

I may end up tearing it down but if I do, I think I will order a spare set of rings just in case. I can't order a new cylinder though. At least not from the regular parts websites.

 

[CTYank]

I am thinking I will use the Lucas oil at 32:1 and see what it looks like. Though maybe I should use Stihl ultra. Why do I feel like this is now an oil thread?



It is obvious that his was not run hard enough by the previous owner. I hope to remedy that situation!

I may end up tearing it down but if I do, I think I will order a spare set of rings just in case. I can't order a new cylinder though. At least not from the regular parts websites.

I've run my '70s Echo trimmer/brushcutter on 40-50:1 fully-synthetic oil from back before the flood. Still runs like new.

Rather than who's on the oil label, I look to the specs. Can't use the high-price label as lube. I use the same in all 2-strokes: JASO FC/FD AND ISO-L-EGD. Some "dino" oils can't meet those. Bailey's has one of the best buys on such full-syn oil.

 

[Gypo Logger]

Running it hard makes sence, but don't lean it out yet or the carbon gets hot and can cause a seizure. Better to pull the jug and clean it all up.

 

[HarleyT]

Carbon will build up also if the shield has been removed. Go ahead and pull it down and slap some new rings in it, it only takes a few minutes. I worked on one in the 1990s, that was still being used daily by some local horse farm. It started and ran OK,
but had no real zip to it. I pulled the muffler, and one of the rings had worn into 2 pieces, and the other one was almost there.
It still started and ran. I cleaned it up, slapped some new rings in it, and it went back to the farm for another 15 years or so.....

 

[Marshy]

What's your reason for wanting to rebuild it? You don't know the compression but feel compelled to dive into the engine when it seems to run fine?

 

[pantelis]

Open it man and see what going on there, maybe need a good cleaning or new rings, its a half hour procedure and cost about nothing.
good luck

 

[jughead500]

Yeap blow by.usually worn rings or rings that didnt seat.saw it in bikes that were broken in on synthetic oil.don't think thats your case.i'd re ring or at least try what fear of pavement said first.

 

[KG441c]

Yamalube ring free at your local bike shop cuts carbon pretty good

 

[ANewSawyer]

Wow! Thanks for all the help!

I've run my '70s Echo trimmer/brushcutter on 40-50:1 fully-synthetic oil from back before the flood. Still runs like new.

Rather than who's on the oil label, I look to the specs. Can't use the high-price label as lube. I use the same in all 2-strokes: JASO FC/FD AND ISO-L-EGD. Some "dino" oils can't meet those. Bailey's has one of the best buys on such full-syn oil.

You can read the label for Lucas oil here.
http://www.oreillyauto.com/site/c/d....oap?ck=Search_N2385_-1_-1&pt=N2385&ppt=C1941

Running it hard makes sence, but don't lean it out yet or the carbon gets hot and can cause a seizure. Better to pull the jug and clean it all up.

This isn't a big deal. Seizure would be a big problem

What's your reason for wanting to rebuild it? You don't know the compression but feel compelled to dive into the engine when it seems to run fine?

Seems to run fine now. What if I use it for an hour and it locks up on me? What am I going to damage by cleaning or reringing? If you think that I am going to damage it, TELL ME!

I did have a moment this morning when I thought the cylinder bolts were frozen. But I got them to pop loose. I thought at first that I had broken the first bolt but they all popped like the first.

Yeap blow by.usually worn rings or rings that didnt seat.saw it in bikes that were broken in on synthetic oil.don't think thats your case.i'd re ring or at least try what fear of pavement said first.

.

I still have that Chem Dip carb soak. The can says it removes carbon on pistons. Couldn't I just take the piston off and soak it for a couple of hours? I don't think it would be wise to leave it in there long.

 

[CTYank]

Before I'd suggest pulling the cyl., I'd make a compression test, to see just how the rings are sealing. Then check again now and then, since it's so simple to do. Simplest compression check available is "does it start?", in that you'll need 90-100 psi to get to start.

Anything you take apart, be sure to note carefully where it came from, so it can go back exactly the same. Parts do bed in.

Be sure to give us some feedback as to how this works out for you. And, how little $ you got away with in parts.

 

[Marshy]

Seems to run fine now. What if I use it for an hour and it locks up on me? What am I going to damage by cleaning or reringing? If you think that I am going to damage it, TELL ME!

I guess Im a simple person and believe in "if it aint broken dont fix it". Other wise you might "fix it 'till its broken".

Do you have any reason to believe it would lock up? If you do, you havent shared that with us. I dont see any score lines in the piston or on the rings. It might have been ringed before you owned it and that could explain the carbon on the piston but those rings look fine to me. Nice and shiney and no transfer anywhere. The real deciding factor IMO to go into a top end is how much compression it makes. Im just failing to understand why you feel the need to go into the top end, is it just what you found when you looked into the evhaust port? Does it have bad performance etc..?

 

[ANewSawyer]

Before I'd suggest pulling the cyl., I'd make a compression test, to see just how the rings are sealing. Then check again now and then, since it's so simple to do. Simplest compression check available is "does it start?", in that you'll need 90-100 psi to get to start.

Anything you take apart, be sure to note carefully where it came from, so it can go back exactly the same. Parts do bed in.

Be sure to give us some feedback as to how this works out for you. And, how little $ you got away with in parts.

I don't have a pressure tester and, really, the reason I would take it down is mainly for cleaning. But also so I can look it over visually. And post pics too. CAUSE I HAVE NO IDEA WHAT I AM DOING!!! And I am thoroughly enjoying it.

I guess Im a simple person and believe in "if it aint broken dont fix it". Other wise you might "fix it 'till its broken".

Do you have any reason to believe it would lock up? If you do, you havent shared that with us. I dont see any score lines in the piston or on the rings. It might have been ringed before you owned it and that could explain the carbon on the piston but those rings look fine to me. Nice and shiney and no transfer anywhere. The real deciding factor IMO to go into a top end is how much compression it makes. Im just failing to understand why you feel the need to go into the top end, is it just what you found when you looked into the evhaust port? Does it have bad performance etc..?

No, I don't have a reason to think it will lock up. But I want to eliminate that carbon, just in case it could cause a seizure. I think that when I take it down, that I won't find any scoring. If I had a pressure tester, I guess I could test it and let it go. But the only way I have of checking it is visually.

Like I said before, it seemed to run fine when I used it but I am so much a novice that I could have missed something when it was running. All I am saying is that it couldn't hurt to open her up and have a look around.

 

[HarleyT]

Back to the carbon. On the piston top, is it shiny or dry and powdery looking?

Take a pick or tiny screwdriver, and carefully push in the rings and check for movement, if you notice much movement, your rings are likely getting thin.
As far as getting too dependent on the use of a compression gauge, I don't rely on them too much..

carbon buildup gives you false compression readings, I only use a compression gauge
when I am selling a somewhat complete chainsaw carcass on Ebay.


I have seen saws with horribly disfigured pistons give high compression readings.

Also, I ask again. Is the grass shield/cutter present on the trimmer?