Stihl 260MS Pro find

[TrekJeff]

Been lurking and ready all the great input on this site for a while and thought I'd throw this out there for some suggestions.
I recently came across a 260MS Pro in a mystery box I bid on at an estate sale. Saw looks great, but pull on the cord to start, and nothing even moves, like the thing is seized up.
What/how should I go about seeing if this thing is salvageable? I was looking online for parts ect and also saw that this came with either a 44mm or a 44.7mm piston.....are there markings on the OEM piston to identify the size or do I need to get a big micrometer?

 

[JonCraig]

First off, pull the muffler and take a picture of the piston. Post it here and you'll get a ton of advice.

 

[blsnelling]

Most MS260s are 44.7mm. You'll have to pull it apart to find out. It's all guessing until you do. Stick with OEM. Most pistons are cheap.

 

[HarleyT]

This bulletin addresses that. What is the serial number?

 

[TrekJeff]

Pulled the top end off and the exhaust side of the piston is dimpled on the edge and has scoring at the face of the exhaust. Found the serial number and it's a 44.7 series. Before I got things apart it was still seized, the flywheel but came off with little trouble, but the torque I used was enough to free the piston and the nut. Once the piston was free, the crack case rotated freely with out binding or slop. So it looks like I'm looking at new piston, things, gasket.
The rings on this are seized on the exhaust side, but free to expand on all other surfaces.

 

[TrekJeff]

Forgot to add pictures Piston and inside of cylinder

 

[Mad Professor]

Looks like you can salvage the cylinder. Is that a dent/chip on roof of ex port or just some transfer?

Try to clean the saw up better before you take it apart then there will be less junk falling into the crankcase.

Try to find out what made it seize. Could be a straight gas but make sure there are no air leaks. Crank seals come in a gasket kit.

 

[Mad Professor]

This bulletin addresses that. What is the serial number?

Is there any advantage/reason to add the muffler heat shield on the older 44mm saws? maybe run a little cooler?

 

[JonCraig]

If you're going this far, replacing anything rubber is cheap insurance. Crank seals, etc.

 

[TrekJeff]

Looks like you can salvage the cylinder. Is that a dent/chip on roof of ex port or just some transfer?

Try to clean the saw up better before you take it apart then there will be less junk falling into the crankcase.

Try to find out what made it seize. Could be a straight gas but make sure there are no air leaks. Crank seals come in a gasket kit.

That is a dent....I was able to touch up the bearing surface.....and yes, great point. I got ahead of myself when tearing into it. I would have smacked my brother if he ever tore into an engine without degreasing and covering an intake manifold.

 

[grizz55chev]

That is a dent....I was able to touch up the bearing surface.....and yes, great point. I got ahead of myself when tearing into it. I would have smacked my brother if he ever tore into an engine without degreasing and covering an intake manifold.

Read up on pressure vac test before you run your new rebuild. If you do not test the saw before running you will likely be doing it again.

 

[TrekJeff]

Read up on pressure vac test before you run your new rebuild. If you do not test the saw before running you will likely be doing it again.

Funny, I was looking that up as I saw you had responded. Gota love YouTube

 

[blsnelling]

It looks to me like something was stuck into the exhaust port as a piston stop. If you hope to use that cylinder, that bulge in the cylinder will have to be ground down. Otherwise, that cylinder is ruined.

 

[TrekJeff]

It looks to me like something was stuck into the exhaust port as a piston stop. If you hope to use that cylinder, that bulge in the cylinder will have to be ground down. Otherwise, that cylinder is ruined.

That's what I was thinking too, you can see the matching dent on the piston. I knocked the edge down but will have to make sure all surfaces are flush. Gota love mystery boxes at estate sales. Once this one is back together an running, I have my grandfather's old Jonsered 630 Super II to refurbish.

 

[TrekJeff]

It looks to me like something was stuck into the exhaust port as a piston stop. If you hope to use that cylinder, that bulge in the cylinder will have to be ground down. Otherwise, that cylinder is ruined.

What would be the best way to address that dent? I'm searching the site, seeing your comments on the topic. The only cylinders I've ever honed out were engine blocks, but with these ports how do you go about honing?

 

[grizz55chev]

What would be the best way to address that dent? I'm searching the site, seeing your comments on the topic. The only cylinders I've ever honed out were engine blocks, but with these ports how do you go about honing?

Look up the Master Mind method of removing transfer, do it on YouTube or google.

 

[blsnelling]

What would be the best way to address that dent? I'm searching the site, seeing your comments on the topic. The only cylinders I've ever honed out were engine blocks, but with these ports how do you go about honing?

A hone is not the answer. You'll have to use a stone or something similar to make sure there are no high spots.

 

[TrekJeff]

Look up the Master Mind method of removing transfer, do it on YouTube or google.

Yep.....I'm looking at just getting the piston and jug....the rotary tools I have aren't going to get th ejob done...price of the tools vs price of a new cylinder/piston...New parts for now.

 

[grizz55chev]

Yep.....I'm looking at just getting the piston and jug....the rotary tools I have aren't going to get th ejob done...price of the tools vs price of a new cylinder/piston...New parts for now.

If you have a drill you can do his method, I took a bolt and sliced it with a hacksaw, folded a piece of sandpaper and went to town. That cylinder is salvageable.

 

[TrekJeff]

Cool, I'll give it a go then post pics for evaluation before I put things back together. As soon as this is done, the Red is next and that thing was a beast when it ran...I know what happened to that..."one" of Gramp's grand kids learned about "Mixed" gas.....sort of how it was given to me when gramps passed. Still feeling the willow branches after that day and it was 35 years ago.