Reasons For Excessive Carbon Buildup?

[Slang]

I'd like for you guys to look at these pictures and give me your opinions if you would. After I gave this saw a good cleaning, I decided to pull the muffler off, and see what the cylinder exhaust port and front side of the piston looked like. There is quite a bit of carbon build up around the port, but there are not any scratches, gouges, or aluminum dust or flakes on the skirt, or top of the piston, or the ring. I have not done a comp test on this motor myself, but I was told by the guy that I bought it from, that he did in fact do one recently, and it held between 110-115 psi. Ain't that kinda low? And here again, check out the spark plug (Autolite 2976) I believe? It's a little wet around the threads. And, there was not a gasket between the muffler, and the exhaust port.

What would cause the excess carbon build up around the port? (no gasket)? (blow By)? (stuck ring)? Or, just running the carburetor fuel mix way too to rich? or all of the above? He said that he had always ran a 32:1 gas/oil ratio, if that might have something to do with it. If this carbon build up isn't anything to be concerned with, as far as the condition of the top end is concerned, is there a way to clean it up to a smoother port surface? or would there be too great of a chance of some of it getting into the combustion chamber, and causing even bigger problems?
Tell me what you think.
Slang

 

[CTYank]

I wouldn't call that excessive. Mainly, it looks to not have beem worked too hard. Chainsaw engines need to be worked long, hot and hard, once broken in, to keep them in good shape. Wouldn't hurt to use less oil in the mix.
Standard suggestion is to scrape exhaust port with wooden tongue depressor, with piston near TDC. Don't let the carbon chunks get into the chamber (use vacuum) since they're like mini-diamonds- they can machine the piston skirt.
That's the reason for muffler screens, so glowing chunks don't set the woods on fire.

 

[jus2fat]

+1 what CT Yank said...that's really not bad at all - just too much oil in the mix...no need to use more than 40:1 mix

I run synthetic oil at 3 oz to a gallon and that comes out to about 42.7:1 ratio.

J2F

 

[roosterhog]

That ain't bad. The plug is supposed to be about that color.

 

[Slang]

That's great to hear, and thank you both very much for your help. After I had blown the water off of the case with my compressor, and the case had completely dried, I let it sit overnight on a paper shop towel. I wanted to see if I could find out where all of that excess oil was coming from out of the clutch side. Sure enough, there was a nice wet spot around the bottom right hand side of the case. I'm thinking the RH crank seal behind the small cover plate is seeping oil, more so when the saw is hot, and slower when the saw is cold. Does it take special tools to replace this seal? or can't I just make a "seal knocker" out of a short piece of PVC or something that would be the same O.D. as the flat side of the replacement seal, so as to gently tap the new one into place without distorting it? I have done this before on other engines, and axle housings etc. and it worked in a pinch very well. Here's a picture of the leaking area for reference.
And thanks again.

 

[CR888]

Everything looks fine there...l would not touch a thing. lf you want less carbon use full synthetic oil but if l were you l'd run any good oil, l don't like FULL synthetic and decide what mix ie 40:1 50:1 and retune the saw for that mix. Run as fresh mix as you can and everything will be fine. From what l can see from the pic that piston still has its machining marks on it. A little carbon is no problem, its certainly not excessive. lMHO that saw has been treated really well and l dont believe the piston would look as good having run FULL synthetic oil. l say keep running a good semi synthetic or good petrolium base oil and that saw will run a long timeto come. Good luck!

 

[CR888]

That's great to hear, and thank you both very much for your help. After I had blown the water off of the case with my compressor, and the case had completely dried, I let it sit overnight on a paper shop towel. I wanted to see if I could find out where all of that excess oil was coming from out of the clutch side. Sure enough, there was a nice wet spot around the bottom right hand side of the case. I'm thinking the RH crank seal behind the small cover plate is seeping oil, more so when the saw is hot, and slower when the saw is cold. Does it take special tools to replace this seal? or can't I just make a "seal knocker" out of a short piece of PVC or something that would be the same O.D. as the flat side of the replacement seal, so as to gently tap the new one into place without distorting it? I have done this before on other engines, and axle housings etc. and it worked in a pinch very well. Here's a picture of the leaking area for reference.
And thanks again.View attachment 348962

l would say that is bar oil.

 

[Slang]

Man, .... you boys are my hero's! I have learned more from you folks on this site than I have in last 30 years from the local small engine crowd around here in my territory. This local bunch around here, either doesn't know, or they just refuse to tell me the truth. I hate a freakin' liar, their bad for your soul. ;-)

I appreciate every one of you.

Slang

 

[jus2fat]

[QUOTE="CR888, post: 4806121, member: 109954" lf you want less carbon use full synthetic oil but if l were you l'd run any good oil, l don't like FULL synthetic. l don't believe the piston would look as good having run FULL synthetic oil. l say keep running a good semi synthetic or good petrolium base oil and that saw will run a long time to come. Good luck![/QUOTE]
--------------------------------------------------------------------------------------------------------------------------------

Just got to ask..why you don't like the full synthetic version...with a blend you don't know what the ratio is.

My stihl rep told me to not buy / use the stihl "blend" because it only has ~ a 20% synthetic and 80% dino ratio..so it's a rip-off.

Many new Hi-Po cars come delivered with full 'syn'...like Corvette..Porsche..Ferrari etc.

J2F

 

[CTYank]

Synthetic oils were developed initially for jet engines: very expensive engines that experience very wide temp ranges. If at all possible, the only engine oil I'll use is full synthetic, not dino, nor blend. Not interested in hearing "wives' tales" thanks, just how lube meets specs.

 

[Marshy]

Dont want to turn this into an oil debate but there are plenty of facts, tests and publications that explain the advantages of synthetic oil vs dino oil. Use what you can afford but recognise there will be long term benefits to useing the synthetic.
As previously stated, try about 40:1 and you should get less smoke and less carbon.

 

[jus2fat]

CT Yank...remember when synthetic first came out and folks said it was just too slippery and the rings wouldn't seat right.

Folks generally just reject change (includes me)...but then folks thinking you can go 30,000 miles between oil changes...not this old man

J2F

 

[Agrarian]

That's great to hear, and thank you both very much for your help. After I had blown the water off of the case with my compressor, and the case had completely dried, I let it sit overnight on a paper shop towel. I wanted to see if I could find out where all of that excess oil was coming from out of the clutch side. Sure enough, there was a nice wet spot around the bottom right hand side of the case. I'm thinking the RH crank seal behind the small cover plate is seeping oil, more so when the saw is hot, and slower when the saw is cold. Does it take special tools to replace this seal? or can't I just make a "seal knocker" out of a short piece of PVC or something that would be the same O.D. as the flat side of the replacement seal, so as to gently tap the new one into place without distorting it? I have done this before on other engines, and axle housings etc. and it worked in a pinch very well. Here's a picture of the leaking area for reference.
And thanks again.View attachment 348962

Did I miss it or did you not say what model of saw this was? With that info, we could help you more as to the source of the bar oil leak.

 

[Agrarian]

Dont want to turn this into an oil debate but ....

opcorn:

 

[Slang]

Did I miss it or did you not say what model of saw this was? With that info, we could help you more as to the source of the bar oil leak.

Forgive my ignorance, 1996 year model straight 268.

 

[Slang]

I wouldn't call that excessive. Mainly, it looks to not have beem worked too hard. Chainsaw engines need to be worked long, hot and hard, once broken in, to keep them in good shape. Wouldn't hurt to use less oil in the mix.
Standard suggestion is to scrape exhaust port with wooden tongue depressor, with piston near TDC. Don't let the carbon chunks get into the chamber (use vacuum) since they're like mini-diamonds- they can machine the piston skirt.
That's the reason for muffler screens, so glowing chunks don't set the woods on fire.

Wouldn't running a thinner fuel mix of 40:1 or so, also be a hotter fuel mix, as well as being a cleaner mix, and burn most of that carbon up and blow it on out of the muffler at operating speed?

 

[anlrolfe]

Unless you've got an old low RPM saw I'd stay 40:1 or thinner.

Have you checked that compression again? carbon buildup can stick the rings.

Not knowing your comfort level with carb adjustment. its better to ere thick or hire it done.

Take-out chinese chop stick to scrape the carbon. Wittle it to any shape you want.

 

[Slang]

Unless you've got an old low RPM saw I'd stay 40:1 or thinner.

Have you checked that compression again? carbon buildup can stick the rings.

Not knowing your comfort level with carb adjustment. its better to ere thick or hire it done.

Take-out chinese chop stick to scrape the carbon. Wittle it to any shape you want.

Nope, I have not checked the compression myself as of yet. I don't have a gauge here at the house. I'm gonna bolt the recoil, and the muffler back on it tomorrow morning, and take it down to the hardware store in town. There's a young kid there that works on small engines and he has a gauge. I agree with you on the thick fuel/oil mix sticking piston rings. I thought about that too, and I also agree with the other folks on here about the thicker mix building up carbon. The old timers used to say that it was cheaper to replace spark plugs, than it was to replace motors. And that is true to a certain extent, but the thicker mix absolutely creates its own set of problems over time as well, so it seems.

When I get back home tomorrow I will get back on here, and tell you all what the compression ratio truly is. Then, I will feel much more confident about how healthy the inside condition of the combustion chamber is before I bolt everything back together and put it to work. I want to see what the ratio is for myself, and not what someone else told me it was. Just peace of mind I guess.

Thanks for the input

 

[KenJax Tree]

The oil ratio has nothing to due with carbon build up as long as the saw is tuned to run at that ratio i run 32:1 with high end synthetic oil and have zero carbon build up.


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[zogger]

What? Excessive carbon build up? It's in all the dang papers! Some people say it ain't so, no way, it is so! Not sealing cracks around doors and windows, big huge mambo mommas driving around gangs of fatkids in SUVs, burning huge electric signs at night so the dang space alines know to drink coke and wear nike shoes! Fossil fuels man, too much carbon!

And you know what happens next, planet heats up, turns back into the hot swamp scene action, a few drunk deranged sciencetwits get to playing around with recombinant DNA and gene splicing, and, before you know it, freeking dinosaurs stomping around!

Boom! Boom! Boom! ROARRRRRAARRRRR!

Then they look down, yum! Roly poly pre-stuffed slow ground monkies! Chomp! Burp! Taste jiss lak bacon! Dinosaurs love bacon!

See, excessive carbon build up, just say no, or THIS happens!