Stihl S10 make work questions?????

[7oaks]

I recently purchased a Stihl S10 that looks in pretty good shape. I filled the oil tank and gassed it with (25:1) mix. It started right up and seemed to idle and rev nicely.

I went through a half tank of gas cutting some firewood just to check it out and loved its power and torqueness.

However, it started bogging down to the point it died once. I restarted it with a couple pulls then it died again a few cuts later. It then wouldn't restart.

The next day it started right up again but wouldn't idle just kinda raced not WOT but way beyond idle - fast enough that the chain kept moving.

I had checked the compression before starting it the first time and it registered 140psi. I also took off the muffler and looked at the cylinder wall, piston and rings. The cylinder wall and rings looked real good to me but the piston has some brown staining/streaking. The muffler also has a lot of carbon on the outside suggesting to me that it has blow-by at the gasket.

Here are some pics as I know we all prefer pics to verbal descriptions:

This is the saw on the log pile after doing some cutting and after it wouldn't restart...

This is a close-up of the piston and rings...

This is a close-up of the back cylinder wall...

More pics next post:

 

[TRI955]

Piston looks a little scored to me. It kinda looks like somebody has been inside there scuffing the cylinder walls too.....

 

[7oaks]

More pics and questions on my S10...

This is a close-up of the muffler exhaust port. Note that the screen or what ever is supposed to be there has been cut out of somehow gone missing.

This is the other side of the muffler showing apparent blow-by. Would either of these two things cause problems with the engine? If so what damage has been done and how can I correct it?

Finally...On the tip of the bar is this brown stuff. I assumed it was pitch of some type but tried removing it with the normal pitch removal solutions with no luck. Anyone have an idea what they might have been cutting with the tip of this saw and if so how to remove it from this pretty nice bar?

Thanks for any help suggestions anyone might have for these problems.


...Carl

 

[blsnelling]

You will need a new piston and rings at a minimum. You may be able to clean up the cylinder. You'll also need to find the source of what caused it to run lean and seize.

 

[teacherman]

Would old carbon/calcium deposits breaking loose cause that kind of piston scratching?

 

[blsnelling]

I know that carbon can cause scoring. I don't know if that's what this is or not. Just one more reason why I like to go through an old saw before I run them.

 

[dave k]

A possible answer for the least important problem, the gunk on the bar, could be a tar based substance like used on railway sleepers and telegraph poles ? In the past I've been tasked with section felling 30' and 50' poles in town centre and got that type of stuff on the bar and saw as well as when based in London I did a couple of jobs for London underground cutting sleepers for night shift maintainance crews and again that type of stuff. Found soaking the bar in diesel and cleaning with WD 40 and carb cleaner used to do the job.
Wonder if a small part of the screen from the muffler was still in the muffler and got into the cylinder ?

 

[7oaks]

Piston looks a little scored to me. It kinda looks like somebody has been inside there scuffing the cylinder walls too.....

Tri...I was wondering if that was damage or a sign that the saw hadn't been used much. I remember Andy once saying something like, the original piston should have cross hatch polishing marks not be smooth. Not sure I am quoting him absolutely correctly but that stuck in my mind.

You will need a new piston and rings at a minimum. You may be able to clean up the cylinder. You'll also need to find the source of what caused it to run lean and seize.

Any idea where I can get a piston and rings?

I know that carbon can cause scoring. I don't know if that's what this is or not. Just one more reason why I like to go through an old saw before I run them.

I've never torn a saw apart so that isn't the first thing I'd do. I've bought several used saws in good looking condition and not had problems so my first instinct with a saw, that looks this good, isn't to tear into it. I did pull the muffler to look at the cylinder and piston (first time I've ever done that as well ) and pulled a pressure test (140psi) before putting gas in and starting it. So if I can get a new piston and rings it looks like I'll be tearing into this saw as I really loved the way it felt when it was cutting.

A possible answer for the least important problem, the gunk on the bar, could be a tar based substance like used on railway sleepers and telegraph poles ? In the past I've been tasked with section felling 30' and 50' poles in town centre and got that type of stuff on the bar and saw as well as when based in London I did a couple of jobs for London underground cutting sleepers for night shift maintainance crews and again that type of stuff. Found soaking the bar in diesel and cleaning with WD 40 and carb cleaner used to do the job.
Wonder if a small part of the screen from the muffler was still in the muffler and got into the cylinder ?

Dave...

Thanks for the insight. I'll try that next. I didn't want to try anything else until I had checked with all the experts here at AS in hopes of not doing any more damage out of ignorance...Carl

 

[Jacob J.]

That was my guess on the bar- creosote. Pistons and rings for those aren't too hard to locate. I know of a number of saw shops that have NOS on their shelves.

 

[fourfivefour]

I believe your S10 uses the same piston as an 08S. Bailey's has an after market piston for cheap.............454

 

[7oaks]

That was my guess on the bar- creosote. Pistons and rings for those aren't too hard to locate. I know of a number of saw shops that have NOS on their shelves.

I believe your S10 uses the same piston as an 08S. Bailey's has an after market piston for cheap.............454

Thanks for the leads guys. I guess I'll try tearing into the saw this weekend and make sure what ccs the piston is.

...Carl

 

[blsnelling]

Make sure you can clean up the cylinder before buying a piston.

 

[7oaks]

Make sure you can clean up the cylinder before buying a piston.

Will do. Any idea who sells cylinders if it is bad?

Also I need to measure the cylinder as there were two sizes as per Acres:

47 mm (1.85 in.) early version was 44 mm (1.73 in.)

I'm not sure how to tell if mine is the new or early version without actually measuring the piston...Carl

 

[7oaks]

I know that carbon can cause scoring. I don't know if that's what this is or not. Just one more reason why I like to go through an old saw before I run them.

Also Brad...

Have you ever seen this type of muffler blow-by. Is this an indication of some problem and could it have caused the piston scoring?

 

[blsnelling]

It just looks like typical carbon buildup. Carbon can and does cause piston scoring. When you get the piston out of the saw, post a good pic so that we can see what it looks like. If you're looking for info on cleaning up the cylinder, do a search for "muratic acid" and click the "show posts" radio button.

 

[7oaks]

gottcha!