MS260 Buy another or Repair?

[jughead500]

No boring to 44.7mm that's past the plating.

 

[ChrisA]

Close your eyes, some of these pictures are disturbing...

First two pictures are the original MAHLE piston, scored the most on the exhaust side. Pictures from this afternoon show the MAHLE cylinder.

Third picture is the 'broken' aftermarket piston from ebay. This was the second one, fist one was similar but again I'm pretty sure that was from the broken ring.

Fourth and fifth pictures are from the aftermarket cylinder that were on the saw with the piston in picture #3. Very smooth, no scoring, just that notch on the exhaust port.

 

[ChrisA]

Sounds like a bad experience indeed. The "little crack" when you installed the top end sounds like trouble to me. To me the saw is definitely worth fixing, you just have to
be cautious as to how you install the kit. If I had the green backs for the Mahle kit, I'd pull the trigger on that set. The cost is less than the used MS260 pro you mentioned.
Since I'm not sure the source on the Ebay kit I'm not going to start to crap on the quality, but one I purchased was pretty much unusable. The ports were weird shaped, the
Nikasil was very sketchy -- not even worth trying. (I've personally repaired probably over 200 saws in this series o26, 026 pro, MS260 and MS260 pro, even the little 024).
If you do buy the OEM kit, take some time and replace the fuel line, filter and impulse (if you have not already) and do a pressure vac test before you run the saw. If not,
see if your Stihl parts friend can do it for you.

On another note, those like myself no nothing at this point as to how you tuned the saw. It could have died the last time due to lean seizure because of an improper tune.
Take some time and do some searches here on "tuning a saw" there is a great thread about that, and if you are in this thing to fix, repair and maintain your saws I suggest
you invest in a wireless TACH as well. Keep us posted on the choice and progress. Welcome to AS

Thanks - no tuning done at all, I'll read into that more if I rebuild it again. Say I did go with the MAHLE set, if I did a pressure test and it was successful would that eliminate the chance of ruining another C&P (assuming it was tuned and right fuel mixture) or would there be other necessary tests to perform before running it? You think a Stihl dealer would run a pressure test for me after I fix it haha?

 

[ChrisA]

Do you have some pics or a better description of "the piston broke"? Where did it break? Did you orient the piston in the correct direction? ie, arrow pointing towards the exhaust port?

I posted the pics, let me know what you think. I made sure to install correctly following youtube video by Jeremy Fountain so I am confident that I did have the arrow pointed the right way. I was thinking back to the install tonight though, I only have a star bit driver with a regular screwdriver like grip. I used that to tighten the four bolts holding the top end to the bottom, and took a vise grip to give it a good crank - is that tight enough?

 

[XSKIER]

I'd be parting that saw out and putting my $190 towards a different saw. The $400 MS 260 PRO if you want a saw, the $659 MS 261 C-M if you need a saw.

 

[rich450es]

did you put the arrow on the top of the piston facing the exhaust port ?

 

[fearofpavement]

On the broken piston, are the ring locator pins still on the piston somewhere?

 

[ChrisA]

did you put the arrow on the top of the piston facing the exhaust port ?

Yes

 

[Wood Doctor]

The 2150 picture shows a piston with the head blown apart upwards. That's caused by ring seize. When the rings got hot and expanded, they collided and had no place to go. So, they blew the roof off.

This never happens to me unless I buy rings separately from the piston. So, I don't do that.

 

[ChrisA]

On the broken piston, are the ring locator pins still on the piston somewhere?

Yes just check tonight they are both there.

 

[nstueve]

The cheap eBay kits can blow up from just about anything. I got a ebay kit that I reviewed a while back compared to the Hyway kit. The cheap eBay kit had voids in the casting everywhere including the spark plug threads.

Chris,
If your piston came apart the case may need to be separated to clean the bearings and inside of the case. Maybe even replace the bearings if there is too much run out in the crank; due to piston shrapnel. If you we're closer I would let you trade it in as a core and sell you one of my rebuilt units. Do you still have the OEM cylinder?

 

[Stihl Ohioan]

OEM all the way . You get what you pay for!

 

[moojpg2]

Ring end gap guys, if its too tight it needs to be filed a little wider. No different than building a v8. Put the ring square in the bore, there should be a certain amount of clearance. Not sure off the top of my head what the gap should be on a chainsaw but very likely some chinese rings are not perfect. Any time u install new rings in motor the end gap should be checked.

 

[ChrisA]

The cheap eBay kits can blow up from just about anything. I got a ebay kit that I reviewed a while back compared to the Hyway kit. The cheap eBay kit had voids in the casting everywhere including the spark plug threads.

Chris,
If your piston came apart the case may need to be separated to clean the bearings and inside of the case. Maybe even replace the bearings if there is too much run out in the crank; due to piston shrapnel. If you we're closer I would let you trade it in as a core and sell you one of my rebuilt units. Do you still have the OEM cylinder?

I do still have the cylinder, see pictures earlier in the thread to see the scoring...

 

[nstueve]

Just get a meteor piston, replace the oil seals and fuel lines and leak check it all before you run it. You should be running just fine at 1:1 turns out on H & L on the carb. Best thing you can do is mechanically clean the scoring with a mandrel and emry cloth.

 

[Stihlofadeal64]

I don't believe with the chunk out around one of the ports that the cylinder is able to be reused (if I see
the picture correctly). Hope the OP has his saw up and running by now. Keep us posted!

 

[computeruser]

Tangentially related: since when did used 026/260s in good shape start going for $400? I thought they were $200-250.