Stihl MS200T: is this cilinder toast?

[MarkB]

The other day i ripped the fuel line on my ms200t.
I got a new fuel line and the saw looked fine after that.

Yesterday i was using the saw again and it started smoking and died on me.

I had a look through the exhaust port and i noticed some scratches on the piston. Today i took it apart to investigate further. I think the piston is gone but i'm not sure about the cilinder. With my fingernail i can feel some very light scratches on the exhaust side of the cilinder, but i'm not sure if it's gone too. I have never done a cilinder or piston job before soo i would like some advise on this cilinder.

Here are some pictures:

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• MarkB
• Jun 1, 2019

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• MarkB
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• MarkB
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• MarkB
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• MarkB
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• MarkB
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• MarkB
• Jun 1, 2019

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• MarkB
• Jun 1, 2019

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• MarkB
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• MarkB
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• MarkB
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• MarkB
• Jun 1, 2019

 

[cuinrearview]

I bet that cylinder will clean up just fine, but you never know until you start in on it.

 

[PogoInTheWoods]

It should..., and the damage looks to be below the ports so a new piston and rings is all it should need. Damage looks like debris ingestion scuff and maybe some carbon smear to me.

 

[lone wolf]

It will clean up but the trick is you got to do it right! If you go too light on the cleanup it will stay there if you go too heavy you can wipe it right out. Now you must find the reason it scored in the first place or it could happen again and you wasted time and money. It should be rebuilt and vac and pressure tested . Don't use a China crap piston. Use OEM piston and seals. You need a piston, gasket and seal set,fuel line ,intake line and you must check the intake boot for tears if there is a slight tear replace it also.

 

[MarkB]

Before i took it apart i did a pressure and vacuumtest. Both were fine. Intake boot and line are also fine.

Could the ripped fuel line have caused a lean condition? Or maybe the debris that's on the sparkplug end of the cilinder and on top of the piston came loose like PogeonTheWoods suggested

I will try to cleanup the scratches with muriatic acid first.
If the scratches cleanup fine should i also clean up the debris thats at the sparkplug end of the cilinder and if so how?

 

[PogoInTheWoods]

I wouldn't jump right in with acid until you determine what the streaks actually are. Even if they are from aluminum transfer from the piston, a safer method for removal would be some 240 ~ 320 grit paper followed by some Scotch-Brite (or equivalent) to finish it off. Then thoroughly wash in hot water with dish soap and rinse well before wiping down with a soft rag or paper towel. It should show no residue from the cylinder wall.

The danger with acid is having it go where it shouldn't go, as in direct contact with bare aluminum. It will eat it quickly and there's no turning back. If there are actual gouges in the cylinder plating that expose the aluminum underneath, acid will ruin what may otherwise still be a perfectly usable cylinder.

As for cleaning the combustion chamber, there are a few ways to go. I personally use a soft wire brush chucked up in a 3/8 drill..., and I go real easy. Solvents are another option, but vary in their results depending on the product and the severity of the buildup.

You would obviously need to scale these methods to the size of the 200T cylinder, but they will work quickly and effectively in determining if the cylinder can be salvaged.

 

[MarkB]

Thanks i will try that first then. I hope it just "wipes off" this way.

 

[PogoInTheWoods]

If the streaks are actual scratches they can be sanded smooth and the cylinder re-used without a problem. The key there is smooth.

 

[lone wolf]

Thanks i will try that first then. I hope it just "wipes off" this way.

Even if it all dont and you have a thin line it will work. Clean it up and see. You cant keep sanding though you will burn the plating off !

 

[MarkB]

I'm afraid i f*cked it up.

I first tried with scotchbride, fine grid sanding paper and some wd40. Not everything would clean up.
So i went for the Muriatic acid (<10%) real carefull. Just let it bubble for a minute and then neutralize it with baking soda. After three times almost everything on the lower end of the cylinder was gone exept for one tiny spot. I went in again one last time with the acid but after neutralizing it i could not belief my eyes. The chrome layer on this small spot was gone!?

This is not good at all.
Have a look and let me know what you think:

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• MarkB
• Jun 3, 2019

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• MarkB
• Jun 3, 2019

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• MarkB
• Jun 3, 2019

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• MarkB
• Jun 3, 2019

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• MarkB
• Jun 3, 2019

 

[PogoInTheWoods]

Many of us have run much, much worse after a clean-up.

That's actually a really nice job even with that one little spot. I'd run it and not look back. Since it's below the exhaust port it won't see direct ring contact and additional wear should be minimal for quite a while (if ever) using a good synthetic mix oil at 40:1.

I say good job and some valuable lessons learned in the process.

 

[MarkB]

That is a nice suprise. Thank you PogoInTheWoods. I thought the cylinder would be toast by now.

Ok than, the piston kit is on it's way from the UK. I will report back when i have the saw in one piece again or if i'm running into more problems.

 

[MarkB]

Today i got the saw back together. I did a vacuum and pressure test before starting it up which was ok. Compression test also looked fine.

When i started it up it looked ok but i ran into some problems with the accelleration and idling. I resetted the carb H screw to the standard 3/4 turn back and the L screw to the standard 1 turn back but the saw still seems to hesitate a bit on accelaration. Also the idling is not really stable. I leaned the L screw a bit and accelaration was better but then it would die on idle even after i turned the Idle up a bit. The saw was hard to restart after that as if the carb was all dry.

Tomorrow i will get the carb out and do the carb cleaner routine. Hope that will solve the problem.

 

[Mad Professor]

Dies on acceleration is usually lean on low. Might have to go back/forth with low and idle.

Check out carb, rubber, metering needle/seat and fuel screen.

Did you do fuel filter with fuel line?

 

[lone wolf]

Try one turn out not 3/4 before you tear it apart and report back.

 

[blsnelling]

I'm betting you need a new carb, or to plug the excel pump passage.

BTW, I highly doubt the acid caused that spec of NiSi to flake. I don't see it being a problem at all.

 

[MarkB]

Try one turn out not 3/4 before you tear it apart and report back.

Will try that first thing tomorrow.

 

[MarkB]

Dies on acceleration is usually lean on low. Might have to go back/forth with low and idle.

Check out carb, rubber, metering needle/seat and fuel screen.

Did you do fuel filter with fuel line?

Fuel filter was replaced with the new fuel line, but i will check just in case tomorrow.

 

[lone wolf]

Will try that first thing tomorrow.

That might do it.

 

[MarkB]

That was easy lone wolf!
I turned back the H screw 1 full turn instead of 3/4 and the saw was fine after that. Maybe just a tiny little bit rich on WOT but hey, it's not a production saw.

Funny that it says 3/4 back on the saw. Why?

I'm happy with my old 200t up and running again!

Thanks everyone for the help on this one.