Probably a stupid question about an MS660

[Ocala]

Hello again all.

So please excuse the lack of experience here.

I bought a used MS660 recently. I haven’t had too much luck so far buying used saws lol.

Anyway, after a bit of cutting I’ll say it’s the most awesome saw I personally have ever used. Starts easy and keeps running.

However, I’d noticed a bit too much flex and determined the several of the annular buffers were toast.

I did cut a lot with it before that happened, and yes let the saw do the work, kept it sharp and didn’t push the saw too hard.

So I’m taking the saw apart to get to them and took a few pics of the piston through the manifold side.

Anyway, the dent in the side of the piston is obvious. I’d noticed a strange sound just before I shut the saw down. Sort of like air passing, hard to describe…

Feels smooth although once I saw this dent I stopped turning the piston anyway.

I’m thinking this could be caused by a piece of a ring and that it obligates me to pull the cylinder, clean everything and examine carefully.

Is that about it?

Finally, I noticed the buffers come in soft, medium and hard… I’m almost afraid to ask any preferences on that?


Great site, thanks all in advance.

 

[Mad Professor]

Piston is a bit worn besides gouge. what is ex like?

Time for a clean up, gasket set/seals, and piston/rings soon.

It will run a bit as is. Don't cheap on parts

 

[ericm979]

I don't see how a piece of debris in the engine would cause that dent but no other damage to the skirt. Usually when debris damages the skirt it's dug gouges and beaten up everything along the way.

It's more likely damage from the person installing it or messing about in the exhaust port. I'd look at the piston crown (as much as you can through the port, shine a light through the plug hole) and the intake side of the piston. If there's no other damage then its really unlikely to be debris. Whoever installed the piston might have dropped it which could weaken it. But chances are if there's no other damage that its ok.

Also, clean the saw up as much as you can before you take it apart so you don't get crap in the engine.

 

[Vintage Engine Repairs]

Hello again all.

So please excuse the lack of experience here.

I bought a used MS660 recently. I haven’t had too much luck so far buying used saws lol.

Anyway, after a bit of cutting I’ll say it’s the most awesome saw I personally have ever used. Starts easy and keeps running.

However, I’d noticed a bit too much flex and determined the several of the annular buffers were toast.

I did cut a lot with it before that happened, and yes let the saw do the work, kept it sharp and didn’t push the saw too hard.View attachment 1081141

So I’m taking the saw apart to get to them and took a few pics of the piston through the manifold side.

Anyway, the dent in the side of the piston is obvious. I’d noticed a strange sound just before I shut the saw down. Sort of like air passing, hard to describe…

Feels smooth although once I saw this dent I stopped turning the piston anyway.

I’m thinking this could be caused by a piece of a ring and that it obligates me to pull the cylinder, clean everything and examine carefully.

Is that about it?

Finally, I noticed the buffers come in soft, medium and hard… I’m almost afraid to ask any preferences on that?


Great site, thanks all in advance.

View attachment 1081137View attachment 1081136

From memory the av rubbers have a code on them referring to their hardness, just replace them like for like.

 

[Ocala]

All great advice thank you all. I was wondering how the dent could be debris related without more damage... I'll clean it up and get some more detailed photos. I did see a spot on the top of the piston that appeared to have been polished, just a very small spot. I wonder if the was someone trying to do some porting?

 

[Bob Hedgecutter]

All great advice thank you all. I was wondering how the dent could be debris related without more damage... I'll clean it up and get some more detailed photos. I did see a spot on the top of the piston that appeared to have been polished, just a very small spot. I wonder if the was someone trying to do some porting?

I wonder if you did not pick up a saw made from a box of all the parts of left over 066/660's from a logging crew.
If the AV's are toast, the impulse and manifold rubber will have had a good flexation work out.
Might be time to clean it down, tear it apart and start replacing all the stuff that wears out.

 

[Ocala]

Piston is a bit worn besides gouge. what is ex like?

Time for a clean up, gasket set/seals, and piston/rings soon.

It will run a bit as is. Don't cheap on parts

Exterior is dirty. Cylinder is OEM but appears cleaner than the rest of the saw.

 

[Ocala]

I wonder if you did not pick up a saw made from a box of all the parts of left over 066/660's from a logging crew.
If the AV's are toast, the impulse and manifold rubber will have had a good flexation work out.
Might be time to clean it down, tear it apart and start replacing all the stuff that wears out.

It was actually just one of them, the large one on the forward right side that was broken. There’s another smaller one that mounts on the upper right side of the case with two bolts that were both simply loose.

I’d planned to replace them all or at least the main ones while I have the saw apart.

I also intend to replace the manifold and impulse tube.

 

[Bob Hedgecutter]

I would be seriously thinking about main crank bearings and oil seals as well.
Check the conrod bottom end bearing real good as well.

That saw has done some hours- everything will benefit from a refresh.

 

[Ocala]

Regarding the crank bearings and seals, I get the benefit of doing this now, but while I’m mechanical enough to get by my understanding is that splitting the case is tricky to get everything to specs.

Would it be worth taking the case to have new bearings and seals and taking it myself from there?

Or is it less complicated than I think?

I’ve pulled heads and clutches etc on engines but this is all new to me.

Another question in this area… I’m used to using torque wrenches to know how tight something is. With the cylinder, I guess I could find a long T27 that would work with a torque wrench, but it seems everyone uses the long T handle torque wrenches.

Appreciate thoughts on this one too, I have unfortunately a few saws that need cylinders

Thanks again everyone.

 

[Bob Hedgecutter]

It is not beyond your scope- but can be intimidating to anyone that has not done so before with case splitting and bearing fitments.
Can be done with basic tooling, but is easier if you have a case splitting tool- however, for a one off build- too expensive a piece to be buying. An old oil pump is handy for 1122 builds, as the PTO bearing used the oil pump as a seat for depth.
There might be someone close to you on this forum with the gear and the knowhow to help out? Walk you through it and show you any tricks of the trade, borrow their tooling and make a friend.

I for one do not use a torque wrench on a saw- never have, probably never will. There are some new kids on the block that will quote you the specs for each screw and torque value for all Stihl products- to each their own, but I have never had a repair or rebuild fail I could blame on torque, or lack thereof from using standard T handle wrenches and armstrong torque.

If you have a few saws needing cylinders, you probably have a few that could do with bearings and so maybe an aftermarket Stihl style case splitting tool set might be worth a look?

When you have it that torn apart, it is not a much larger step to do bearings and oil seals for peace of mind, so when the saw is finished- you can be sure all is well.

 

[ericm979]

I like to use a torque wrench on important fasteners like cylinder bolts. I got an extended T27 3/8" socket drive bit, It wasn't too hard to find.

There's a lot of support for the 660 including aftermarket case tools.

 

[Ocala]

Yeah I get the concept of “having a calibrated arm” but stripping a cylinder bolt thread would REALLY be a bad move.

My uncle was an A&P in the Marines at Andrews. They had this one guy who would always strip threads, so the other guys cut all of his wrenches in half.

Possibly after I’ve done about 10 of them I won’t need it anymore.

When you haven’t done ONE, a bit scary haha.

 

[pioneerguy600]

After a couple dozen you can do them with eyes closed, there are times I think have done them in my sleep.

 

[huskihl]

If you use a T handle, you’re not going to strip any major bolts on a saw. Recoil screws and anything shorter may be an exception because of threading into magnesium and having slightly less reach. Unless you start one cross threaded. At that point, there’s no saying what will happen. But a torque wrench wouldn’t have saved it anyway.