ms260 muffler issue, piston/cyl damage?

I have an MS260,not the pro version, so no adjustable oiler, but oddly it has the decomp switch.

I've been studying the muffler mods people have done on this forum, and thought it worth doing. I just pulled the muffler cover off, and it looks quite different from the pictures I've seen. There's only an inner and outer piece of the muffler, nothing blocking the exhaust port. The exit holes on the muffler are really tiny though. I'm guessing a muffler mod is pointless in this case, since there's nothing blocking the exhaust port. I suppose I could open up the cover with a grid of smaller holes.


While I had the cover off, I took a peek at the piston and cylinder. Note the back end of the muffler is still on the pic's below. I haven't had this saw for too long (new to me), and it works well, but nothing exceptional. I'm wondering if what looks like damage on the piston is robbing me of some performance. The top cover of the saw is burned slightly just above the muffler. It looks like the saw was run pretty hard at some point.


Also, it just sounds weird. I can't figure out what it is, but it sounds almost like a buzzing noise that shouldn't be there at idle. The mix is 50:1 stihl, and it's fresh, and I chucked the previous owner's gas. I tried making a short video of the saw idling (1st attempt at creating/uploading video, using a really old camera), not sure if it will be clear enough. The video is here:

http://s830.photobucket.com/albums/zz223/zapstrap/?action=view&current=ms260_weird_sound.flv

Is it possible the previous owner removed something from the muffler? The carb has L & H adjustments, but the limiter caps are still in place by the looks of things. I'm wondering if this, coupled with the empty muffler, would cause the saw to run a little on the lean side? I did pull the plug out for a look, and it's a tan colour, not wet, or white, doesn't look like the saw's running lean.

As alarming as this is, it starts up easily enough, idles, doesn't hesitate, and cuts decently. Without the decomp switch pressed, it's really not that hard to pull, and I'm not sure if it should be. Is a bit of scoring like this normal?

If its still running I would pull the top off right now. The cylinder may still be useable if cleaned up. Piston and rings are a lot less expensive than a cylinder kit. If you continue to run it you may need a whole top end. I bought an 024 cheap that looked similar and I was able to clean up the cylinder with muriatic acid and it only needed a piston/rings.

I believe somebody removed the baffles from inside the muff and never opened the fuel up. That could be why its scored.

I'd open up the cover outlets a bit on the muffler.

Ex port looks a little greasy, might be running rich. Previous owner might have got carbon into the cyl when modding muffler and that could be carbon scoring on the piston, hard to tell from the pictures.

A member here has OEM P/C kits for $85, shipped.

You'll pay that for a piston and rings at a dealer.

Edit: I'll retract the carbon scoring theory, after having a better look at the intake side of the cyl looks like lean seize or raw gassed

There is no baffle tube in a 260 muffler, or at least the several I have done. It is just an open chamber with ever decreasing outlet holes. You can read for hours on here about 026/260 muffler mods, so I won't re-hash that now.

New piston/cylinder images

Since others have pointed out the images were of poor quality, I've edited the original post to have more useful pictures.

looks wierd more like it was ran without an air filter or water in the gas...

Remove the low speed limiter cap and count the number of turns you get before the needle is seated...

See if the cylinder will clean up with acid, if not PM bcorradi and get a oem kit as mentioned. While she is tore down, a pressure test would be a good idea and would help determine why the p&c is scored.

If you have the adj. carb, open up that muffler, wayyy to restrictive as it sits. A husky 288xp exhaust deflector works great on those. If your carb doesn't have a "H" screw, start looking for a 194 carb and use that one.

pressure test

So, I have an opportunity to learn something new. Hopefully I can get a little step-by-step advice as needed.

My plan:

1. Pull cylinder off, and try to clean it up with muriatic acid.
2. If 1 is a success, order a new piston/rings/gasket set. If 1 is a failure, order a new piston/rings/cylinder/gasket set.
3. Test for leaking crank seals. How? If seals are blown, replace? Can I do this in my garage, or do I need to send the saw out?
4. Test impulse line. I'm really ignorant on this one. What's an impulse line? How do I check it?
5. Inspect fuel line for cracks or leaks. Replace as needed.
6. Remove limiter caps from carb.
7. Drill some holes in muffler (might as well, in for a penny in for a pound).
8. Re-assemble, and retune.

I don't have a compression tester, leak tester, torque wrench, or ring compressor. Are there tricks to getting around all this? I can probably borrow a torque wrench if it's critical for remounting the cylinder, or anything else. I can't think of too much else I need, specialty-tool wise. I do have all the other basic tools one might need.

Have I missed anything?

stderr said:

So, I have an opportunity to learn something new. Hopefully I can get a little step-by-step advice as needed.

My plan:

1. Pull cylinder off, and try to clean it up with muriatic acid.
2. If 1 is a success, order a new piston/rings/gasket set. If 1 is a failure, order a new piston/rings/cylinder/gasket set.
3. Test for leaking crank seals. How? If seals are blown, replace? Can I do this in my garage, or do I need to send the saw out?
4. Test impulse line. I'm really ignorant on this one. What's an impulse line? How do I check it?
5. Inspect fuel line for cracks or leaks. Replace as needed.
6. Remove limiter caps from carb.
7. Drill some holes in muffler (might as well, in for a penny in for a pound).
8. Re-assemble, and retune.

I don't have a compression tester, leak tester, torque wrench, or ring compressor. Are there tricks to getting around all this? I can probably borrow a torque wrench if it's critical for remounting the cylinder, or anything else. I can't think of too much else I need, specialty-tool wise. I do have all the other basic tools one might need.

Have I missed anything?

Click to expand...

If you do a search for pressure vac test there are a couple cheap ways to get this done without a mityvac. Someone around here even has a link to a thread in their sig. The ring compressor is a very handy inexpensive tool to have. Some have used soda/beer cans cut up but for the price I would just get the compressor. Sounds like you are well on your way to me.

Do not dissassemble it yet. Take it to a saw shop and ask for a pressure and vac test to check seals before you break it down. Or, you can buy a vac tester and do it yourself if you can fab some plates to block inlets etc. Pressure test you just need an air compressor running at 10lbs. check fuel line, impuse line, carb boot, tank vent while you are at it

Once you know the case is sealed (or you know what to replace for seals) then proceed to pulling the jug and cleaning the alum transfer off.

You can make a ring compressor out of a yogourt container.

Here is the link to the low budget vac test

http://www.arboristsite.com/showthread.php?t=42768&highlight=leak

And I use zip ties for my ring compressors

subhunter said:

Here is the link to the low budget vac test

http://www.arboristsite.com/showthread.php?t=42768&highlight=leak

And I use zip ties for my ring compressors

Click to expand...

Excellent, thanks for the link. I'm still chuckling about the zip tie as ring compresor...so simple...pure genius...never woulda thoughta that.

Partial Diagnosis, a little progress

After a careful read of Four Paws' budget vacuum tester, I decided to go with Zombiechopper's suggestion, and took the saw to a dealer for a check-up. Their diagnosis:

1. Pull-starter side crank-seal is leaking.
2. Crank bearings are in very good shape: no noise, turn smoothly, very little play.
3. Piston damage has not made it through the top ring, hence it still holds compression and runs. I didn't ask for a compression test, as it seems pointless.

If there's no damage above the top ring, I suspect there's a fair chance the cylinder can be saved. Next step, pull cyl. off, clean it up w. muriatic acid & emery paper. Pic's to follow.

When cleaning up w. acid, I've read the idea is not to get it anywhere except in the bore, where there's been Aluminium transfer. Are there any other things I should be aware of (e.g. should I remove the decomp valve)? Recommended grit for emery cloth? Do I need/want to hone it?

Now I AM NO EXPERT. But I would not suggest honing the cylinder. I would pull the decomp valve out and use the acid in the bore to clean it up. It may take several treatments with the acid from what I have read. I myself have never done the acid. The one I cleaned up was not that bad and I used fine emery cloth and buffed it back smooth. Good luck with your project and keep us posted....

That bugger of a flywheel side 026 crank seal seems to be a common reoccurance. Not only that, they're one of the most difficult to remove without the expensive Stihl tool.

Cylinder Cleanup

I've only done two cylinder cleanups and they were both a little different, but both successful.

A couple of points about the acid:

Only use a small amount in an acid friendly container like a shot glass. Have another small container with a water/baking soda mix handy to neutralize used q-tips and for any spills or slop that may get to the wrong areas -- including on you! Don't re-use the same q-tip as any aluminum on it can contaminate the container of clean acid.

Try to apply the acid only where it is needed -- generously with a q-tip. The aluminum x-fer should start to bubble and smoke. (Be careful of the vapors -- they are very irritating to both eyes and lungs.)

When the smoking/bubbling stops, that's the end of that application in that area. Go to the next area, or rinse clean and start working the area with 320 grit for the rough stuff and 600 for the lighter and/or final pass. If there's still more aluminum, repeat the applications until things are cleaned up and smooth to your satisfaction. You must rinse/clean the cylinder between applications to ensure maximum exposure of any remaining aluminum to the next acid application. A little oil or sanding dust can greatly diminish the effect of the acid.

Above all, be patient. You're not just rinsing out a dirty coffee cup and the process can take some time and repeated effort to be effective -- or not depending on the condition of the cylinder in the first place. Won't know till you take a stab at it unless it's REALLY bad. That's when you just go for the $85 OEM p/c and put things back together.

BTW, roncoinc has a video somewhere of what the acid reaction looks like. I'm sure a quick search would find it.

Good luck.

Poge

ms260 cylinder removal

I removed the cyl. from the crankcase. Here's what I found:

First, the piston:



Next, the cylinder:



It doesn't look that bad to my poorly trained eyes, however I noticed some pitting:



The left image above shows the pits most clearly. The pit on the left, just under the right side of the exhaust port is definitely not transfer, it looks very much like a casting flaw. The one on the right does as well, but it looks much older, and there seems to be smaller pits around it, like the rings have been catching on it.

I'm afraid if I start putting acid on these they're going to make the flaws considerably worse. Opinions?

Time for a P/C kit.

Good luck with it and keep us posted.

Poge