Stihl ms261 piston question (burned)

[MartDalb]

It’s the newer style Stihl saws with the 1 pc cover. Little different than working on the older style where the carb was mounted in the box on the handle. Once you learn the steps and quirks of each model I think they’re easier to work on than the older models

Now im tempted

 

[Mad Professor]

Clutch can get hot from **** build up inside cover. I've seen a 026 cover start to melt from this.

Piston/exhaust looks way too rich. I don't do M-tronics so can't say if it's that or the fuel? Might want to clean that up before you get carbon scoring.

I'm glad I'll never have the joy of working on a M-tronic.........

 

[MartDalb]

Clutch can get hot from **** build up inside cover. I've seen a 026 cover start to melt from this.

Piston/exhaust looks way too rich. I don't do M-tronics so can't say if it's that or the fuel? Might want to clean that up before you get carbon scoring.

I'm glad I'll never have the joy of working on a M-tronic.........

Thanks,Ill make sure to do that! Already started actually!

 

[MartDalb]

Wth...how do people do this?

 

[MartDalb]

Carb side picture.

 

[MartDalb]

Inside carb.

Sticky as hell diaphragm and gaskets etc.

How does it get like this, from so little use? I don't get it? Did he run the saw without filter?

 

[EchoRomeoCharlie]

I see that a lot on saws that are from people who don't know how to sharpen or even don't know that chainsaw chains need to be sharpened.

I took a saw from a guy at work who said it wouldn't start. Told him it was probably just a gummy carb, I'd rebuild it and she'd be back to running. I got it and realized quickly from all the very fine sawdust all over the saw that he had been cutting for quite some time with a dull chain. His air filter was almost completely clogged with fines. The entire saw was covered in fines. Ran through the normal troubleshooting, it had spark, would fire with some fuel down the carb, so it was a fuel problem. Took the carb apart and looked like yours.

I ended up replacing all of his fuel lines, rebuilding the carb, spending an hour cleaning the saw, and sharpened the chain for him. His fuel filter had fallen off at some point, so yeah, it was sucking up all sorts of crap. When I gave it back I told him I sharpened the chain and he said 'They need to be sharpened?!?' So I gave him some pointers and a round file that fit the chain. He texts me two days later after using the saw and was blown away at how fast it cut and how there was no smoke coming from the chain....lol


That saw looks like it has been run with a very dull chain for a long time.

 

[MartDalb]

I see that a lot on saws that are from people who don't know how to sharpen or even don't know that chainsaw chains need to be sharpened.

I took a saw from a guy at work who said it wouldn't start. Told him it was probably just a gummy carb, I'd rebuild it and she'd be back to running. I got it and realized quickly from all the very fine sawdust all over the saw that he had been cutting for quite some time with a dull chain. His air filter was almost completely clogged with fines. The entire saw was covered in fines. Ran through the normal troubleshooting, it had spark, would fire with some fuel down the carb, so it was a fuel problem. Took the carb apart and looked like yours.

I ended up replacing all of his fuel lines, rebuilding the carb, spending an hour cleaning the saw, and sharpened the chain for him. His fuel filter had fallen off at some point, so yeah, it was sucking up all sorts of crap. When I gave it back I told him I sharpened the chain and he said 'They need to be sharpened?!?' So I gave him some pointers and a round file that fit the chain. He texts me two days later after using the saw and was blown away at how fast it cut and how there was no smoke coming from the chain....lol


That saw looks like it has been run with a very dull chain for a long time.

This actually makes a lot of sense! Thanks alot!

Cleaning this thing up, it has this rough, dried in dirt, fine fine sawdust that has sat for some years.

Granted, I repair more than I cut, but my trusted 260 has seen some action over the years, and it never had this fine grit dirt like this. It is actually a pain in the a$$ to clean up!

 

[MartDalb]

Cleaning it....helps.
This machine can't have seen many cut hours?

 

[Wood Doctor]

Please someone explain, what makes the 261 so hard to work on?
Doing 250s 260s etc in my sleep, almost feel like taking this apart and see for myself

Please do that like I did several times and then report back. Make sure it's an M-tronic. Keep track of all the parts on your bench that you must remove to rebuild the top end. And, keep track of all the service manual call backs to other areas in the manual as you go along. It might drive you crazy.

 

[MartDalb]

Please do that like I did several times and then report back. Make sure it's an M-tronic. Keep track of all the parts on your bench that you must remove to rebuild the top end. And, keep track of all the service manual call backs to other areas in the manual as you go along. It might drive you crazy.

Sounds like something I want to avoid, when you put it like that!

Ill be out running the saw within a day or two.
Will post update after that.

Thanks a ton for all the replies and help!

 

[toppers]

My piston started to look exactly like that running on Stihl Motomix when brand new. 8 tanks of Red Armor cleaned it up, awesome stuff. Was very surprised a Stihl product would have such a negative impact on a piston.

 

[Wood Doctor]

Sounds like something I want to avoid, when you put it like that!

Ill be out running the saw within a day or two.
Will post update after that.

Thanks a ton for all the replies and help!

Mart, you might look at it this way. The Stihl dealer's mechanics told me It was a 10-hour job for them to rebuild a burned out 261 M-tronic. They wanted no part of it. It took me 12 hours after a 30-day wait for parts. Stihl was sold out of the slanted cylinder. The others do not fit and will not work. Say, if you get it done and it runs OK, Hooray! It's easier than an MS 441 M-tronic.

 

[bwalker]

Mart, you might look at it this way. The Stihl dealer's mechanics told me It was a 10-hour job for them to rebuild a burned out 261 M-tronic. They wanted no part of it. It took me 12 hours after a 30-day wait for parts. Stihl was sold out of the slanted cylinder. The others do not fit and will not work. Say, if you get it done and it runs OK, Hooray! It's easier than an MS 441 M-tronic.

12 hours? That saw must be a pain in the azz.

 

[Vintage Engine Repairs]

Remove jug, clean rings and lands as well as piston. Check ring end gap and skirt to cylinder clearance and proceed from there. Looks like blow by.

 

[furb]

It’s not that it’s harder just different. There are more parts, that kill switch itself is a pain to get out. I put a piston in a 261 m tronic and cleaned up the cylinder and I’m sure it didn’t take 10 hours but it took a while.

 

[furb]

It’s not that it’s harder just different. There are more parts, that kill switch itself is a pain to get out. I put a piston in a 261 m tronic and cleaned up the cylinder and I’m sure it didn’t take 10 hours but it took a while.

 

[Oldsawnut]

Mart, you might look at it this way. The Stihl dealer's mechanics told me It was a 10-hour job for them to rebuild a burned out 261 M-tronic. They wanted no part of it. It took me 12 hours after a 30-day wait for parts. Stihl was sold out of the slanted cylinder. The others do not fit and will not work. Say, if you get it done and it runs OK, Hooray! It's easier than an MS 441 M-tronic.

The other cylinders fit you just need to get the older top to go with it or trim the plastic on the inside of your cylinder cover

 

[MartDalb]

Update.
Put the saw back together to test it out.

No start, No spark.
Tried New spark plug, brand New.
No spark.

Reset the distance on ignition module.
No spark.

Sigh...

 

[Vintage Engine Repairs]

Update.
Put the saw back together to test it out.

No start, No spark.
Tried New spark plug, brand New.
No spark.

Reset the distance on ignition module.
No spark.

Sigh..

Check the kill wire first, make sure it's not going to ground along its length and check the switch is all functioning correctly. Use a multimeter