Oil or Carbon Staining on Side of Piston on Newish Saw

[sld961]

I bought an MS 261 CM not too long ago. It starts up, runs good. It has 160 psi compression. I started the process of selling it because I need the money. I pulled the muffler off to take some pics of the piston and was surprised to see that most of the piston is a dark color, as if it is stained by oil or carbon.

I looked at the top of the piston and there is not any carbon buildup. I thought that maybe the rings were sticking and that it was caused by blowby, but with 160 psi, is that likely?

At this point, I'm thinking that the previous owner just used too much oil in his mix. If a good quality synthetic oil is used at the right ratio, this should clean up over time, right? There is no scoring that I can see and the machine marks are visible through the staining.

What are your thoughts? I'll add pics in the next post.

 

[sld961]

 

[HarleyT]

Using old fuel mix will leave a varnish scum like that.

 

[sld961]

Will it clear up over time with the use of a good synthetic oil? Does it cause any harm to the saw?

 

[HarleyT]

It doesn't do it any good!! That scum is also on the bearings.

You have 3 choices....

Put the muffler back on and sell it, just use the pic with the compression gauge and moccasin.........

Or else run it hot with fresh fuel and hope it burns off...

Or dis-assemble it and remove the film....

 

[sld961]

Option 1 doesn't work, I can't sell stuff without full disclosure.

 

[bikemike]

My guess was bad mix and restricted exhaust holding gasses and deposits in. The port is really black like cheep 2 cycle or motor oil was used as mix. who knows maybe someone thought chainsaw oil is for gas mix too some ppl are as bright as a burnt out bulb

 

[sld961]

I pulled the cylinder and started to clean up the piston, except there's 2 "defects" on the piston. Not sure what they're from, it looks like there defects? They aren't coming off. I called and ordered a new piston. There's a small scratch below the exhaust port from the one mark, but it won't affect anything because it's below the port. I'll put the new piston in and it'll be good as new.

 

[Blairito]

i just bought a 261 as well, same thing dark piston, but otherwise no wear
was concerned

 

[Full Chisel]

You just wasted money on a piston...IMO that one was perfectly fine.

 

[Gypo Logger]

Using old fuel mix will leave a varnish scum like that.

Agreed, there is a lose of lubrafication and viscousness with old mix.

 

[Full Chisel]

Agreed, there is a lose of lubrafication and viscousness with old mix.

Now you're just makin' up words!

 

[Firemech86]

I had my muffler off of my 261cm this morning, had the same varnish on the piston but not as bad. I have only run the Husqvarna premix in this saw (I can get it locally much cheaper than the motomix or VP ethanol free stuff), I am not going to worry about it. I can't use pump gas here, the 3 stations I have checked all have 20+% alcohol in the fuel. Cost me a saw already.

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[CR888]

I bet full synthetic oil was run in these varnish stained piston 261's. Clean it off and run quality mineral oil, problem solved. I've had 4 ms261's & only when run on synthetics does the varnish build up occur. Happens in short order too. The varnish build up WILL eventually promote blow by, a fact many don't realise when considering full synthetics.

 

[Firemech86]

I bet full synthetic oil was run in these varnish stained piston 261's. Clean it off and run quality mineral oil, problem solved. I've had 4 ms261's & only when run on synthetics does the varnish build up occur. Happens in short order too. The varnish build up WILL eventually promote blow by, a fact many don't realise when considering full synthetics.

I had not heard that the full syn oils caused varnish.... hmm will have to look into that some

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[7sleeper]

Varnish like that is typical when using castor based 2 stroke oils.

Never heard or read before of a full synthetic oil causing any problem like varnishing before. Quite the contrary that full syn cleans the deposits off of the inside of engines. One should always be aware that there are different grades of oil out there. Full synthetic which should be truely full synthetic. Synthetic which is usually a mix of different types of oils (synthetic and mineral). And castor oils mixed into the 2 stroke oil.

7

 

[KG441c]

Thats looking more like ring blowby or rings havent seated

 

[KG441c]

I bought an MS 261 CM not too long ago. It starts up, runs good. It has 160 psi compression. I started the process of selling it because I need the money. I pulled the muffler off to take some pics of the piston and was surprised to see that most of the piston is a dark color, as if it is stained by oil or carbon.

I looked at the top of the piston and there is not any carbon buildup. I thought that maybe the rings were sticking and that it was caused by blowby, but with 160 psi, is that likely?

At this point, I'm thinking that the previous owner just used too much oil in his mix. If a good quality synthetic oil is used at the right ratio, this should clean up over time, right? There is no scoring that I can see and the machine marks are visible through the staining.

What are your thoughts? I'll add pics in the next post.

Previous owner was using Klotz Super Techniplate?

 

[KG441c]

I pulled the cylinder and started to clean up the piston, except there's 2 "defects" on the piston. Not sure what they're from, it looks like there defects? They aren't coming off. I called and ordered a new piston. There's a small scratch below the exhaust port from the one mark, but it won't affect anything because it's below the port. I'll put the new piston in and it'll be good as new.

Is that bottom ring stuck in the ring land?

 

[sld961]

Previous owner was using Klotz Super Techniplate?

Is that bottom ring stuck in the ring land?

This was a year ago, I don't remember the details. I think I put a new piston in.

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