MS260 Piston Pin Circlip Killed Piston

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Ricrhys

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Hi there,
New to the forum, new to chainsaws and to small engines.

I have a Stihl MS260 which I bought a couple of months ago all has been fine until today, it's had really light use so far but today was the longest I've used it for just chopping firewood up at the barn, all of a sudden it just stalled, of course I just went to start it again and it had no compression, then after a few pulls the flywheel jammed.

You can see from the photos that the piston pin circlip has died and caused this damage, what do you think caused it to die? just a dodgy circlip or something worse?

You can see shrapnel in the crank housing so I'll need to clean it out.

Any advice greatly welcome.

Thanks in advance.

Ric
 

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Looks a little dry in there. You'll surely want to split those cases. All the shrapnel got in the bearings too.

Ok so I'll add a new bearing to the list of parts any good sites for part numbers? what would cause it to be dry in there?
 
lack of oil
baileys has high quality aftermarket and oem parts, and there are many other places too
 
I'm using one shot stihl green in 5l of fuel, am I missing something for oil in the crank housing? forgive the questions I'm a bit green myself.
 
Another thing I've noticed are there are no gaskets between the muffler and the cylinder housing, should there be? in the youtube top end rebuild video I've watched there are two.
 
not familiar with one shot stihl green, i use stihl oil that comes in small orange containers that is mixed with one gallon of gas, its idiot proof so i dont have to figure out how much oil for 50-1 or 40-1. i've been using that stihl oil for decades now and never had a problem. i believe there should have been a gasket between muffler and cylinder. I'm not a professional just a hobbyist.
where are you, what country?
there are lots of experts on this site someone will chime in
let me guess you got the saw used and dont know the history of it.
fortunately the ms260 is a great saw well worth rebuilding
 
not familiar with one shot stihl green, i use stihl oil that comes in small orange containers that is mixed with one gallon of gas, its idiot proof so i dont have to figure out how much oil for 50-1 or 40-1. i've been using that stihl oil for decades now and never had a problem. i believe there should have been a gasket between muffler and cylinder. I'm not a professional just a hobbyist.
where are you, what country?
there are lots of experts on this site someone will chime in
let me guess you got the saw used and dont know the history of it.
fortunately the ms260 is a great saw well worth rebuilding

You're correct unfortunately I brought it second hand, I brought the one shot as it's also supposed to be idiot proof, UK based and one of our standard small fuel cans are 5L, so one can one shot. I fully intend to rebuild, will just need lots of help on here.
 
Great, so theres a chance that I did nothing wrong and it's just a crap circlip, would love to know for sure though.

Check to determine if the piston or jug are OEM. If not it was likely rebuilt with Chinese aftermarket crap. When you do the rebuild use preferably OEM parts and especially OEM circlips. When installing the circlips make sure that the notch opening faces either up or down and NOT left or right.
 
Are there any markings to tell if it’s OEM?

what should be on my parts list and to do list?
 

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Are there any markings to tell if it’s OEM?

what should be on my parts list and to do list?

That piston isnt oem. Definitely can tell by the clip thats still in. Also it looks fairly new and i dont see the Stihl markings on top of the piston. Post some pics of the outside of the cylinder and ill tell you if its oem. My guess is somebody fairly recently attempted a quick cheap rebuild and this is the result of cheap parts
 
If its a ms260 then its 44.7mm. The serial number is to the left of the muffler.
Cheers, on another thread in the forum it says that saws before S/N 262xxxxxx were 44mm and after 44.7mm my S/N is 155xxxx, but yet another (on a different forum) thread says they are interchangeable.

I'm guessing I'll be quickly past the £130 I payed for the whole saw in parts to fix this?
 
Hello.

I’ve just done something very similar on an old 038S...might be worth scanning through, lots of good info in there from some very knowledgeable people:
https://www.arboristsite.com/community/threads/038-super-top-end-rebuild.332171/
Something I now know is that if you get an aftermarket piston there is no guarantee that those all important OEM piston circlips will work: I bought OEM circlips for my rebuild but ended up having to use the ones that came with the piston; they might be ok they might not be. I wish I had bought an OEM piston now...even if just for peace of mind.
Yes you will definitely spend more than £130 imo
 
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