M660 Rebuild opinion.

[musch]

I am working on a MS660 saw, and I have a couple questions.

Obviously the piston is scored pretty bad. In the photos you can see two marks where it actually looks like an object was in the way that caused the scoring.

Could this have been from carbon buildup? Or is there another cause that you guys can think of?

Second, the jug looks pretty good EXCEPT at the exhaust port.
Do you think that it could be salvageable? Or should I just start over.

 

[Lakeside53]

You can salvage the cylinder... you need to clean up any burrs from those two dents.

But it looks like your saw ATE something... is you crank in one piece? your bearing AND CAGES intact?

You might be able to salvage the piston too...

The carbon isn't particularly abnormal..

 

[1953greg]

check the decomp valve too. i had 2 to break and one of them to dump the bearings (there are 3 of them and 3 little bity springs) and half the stem into the cylinder.

but from looking at the valve it seems ok. i dont think the ball bearings can get out w/o the stem breaking

freakish, but it happened to me

 

[musch]

But it looks like your saw ATE something... is you crank in one piece? your bearing AND CAGES intact?

I know thats what I was wondering, if some OBJECT got in there.

As far as the crank, thats what is weird. It actually felt like it had pretty good compression, too.
I'm still taking it apart. I think everything is still intact.

The rings seem loose, could they leave those marks?

It wasn't my saw, I got it as a salvage junker. So I don't know WHAT they did to it.. the body, other than dirt, is pretty clean too. opcorn:

 

[musch]

check the decomp valve too. i had 2 to break and one of them to dump the bearings (there are 3 of them and 3 little bity springs) and half the stem into the cylinder.

but from looking at the valve it seems ok. i dont think the ball bearings can get out w/o the stem breaking

freakish, but it happened to me

Now that might actually be it.... I'm checking.

 

[Lakeside53]

The rings look in pretty good shape!

 

[doc874]

066

Is one of the rings in wrong? Upside down perhaps? That would do it because it would stick out just enough to dent the port and chip the piston skirt.

Doc

 

[Lakeside53]

Not rings... you can see the matching dents in the squish band area at the top of the cylinder above the exhaust port.

 

[musch]

There are matching marks toward the bottom on the opposite side :help:

What is the best way to remove the piston, is there a clip tool?

I don't think it was the decomp valve, both it and the spark plug (NKG) appear to be intact.

Lastly, is this amount of play normal around the bearings? I'd rather not tear the whole thing down if I dont have to, but it is gonna need a lot of cleaning.

Thanks for all the help. I'm still learning from this site.

 

[Canyon Angler]

Could those dents have been caused by a couple of loose balls from a broken bearing somewhere?

 

[musch]

Could those dents have been caused by a couple of loose balls from a broken bearing somewhere?

thats what I was wondering. havent found anything yet...

 

[1953greg]

musch

"What is the best way to remove the piston, is there a clip tool?"

use a pointed driver (screwdriver w/ a point) to rotate the c clip such that the end is bout 1/8" from the cutout. then using the cutout, pry underneath the c clip w/ the point to bring the end out enough to get a very small flat screw driver under/behind it.

if u dont want the c clip to disappear u need to cover your hands and piston w/ a cloth when it starts to leave the grove.

dont ask me how i know this. :bang: :bang: :bang:

the play is normal and not adjustable

not sure bout the exhaust ports. i would probably just smooth it up and let it ride.

if the decomp clicks/snaps back n forth its ok. there are 3 spring loaded metal balls bout .030" dia inside it and they detent in a grove when valve is closed. that is why it snaps. i dont think they can get out unless the valve snaps into.
but it sure looks like something very round was in there. probably just 1 and it made 2 dents. my piston didnt have that depth of indention but it had plenty more and i shut the engine off in just couple seconds. but half of the valve, 2 steel balls, and 1 spring made it to the chamber.

 

[musch]

So, would you guys use the muriatic acid here, or am I better off with a hone, or both?

Also, is there a parts or service manual available online for the 66/ 660 series? There are a few other things that need replacing, and/or are missing,
and a couple things I don't even know the name of...
:monkey:

 

[RoyR(MI)]

http://www.arboristsite.com/showpost.php?p=537739&postcount=2

 

[blis]

Looks like you got some bearing balls missing, since those marks on piston seem to be round, id check crankbearings for starters...

 

[PES+]

Are the ring stop pins still in the ring grooves? It does not look like they are....

That crank is pretty much done

 

[Kneejerk Bombas]

What do you see wrong with the crank?

 

[PES+]

Look at the roller directly under the web of the rod...it should be spaced like all the others so there is damage of some sort there cage distortion.......maybe he can force the rod to the other side of the crank web clocked the same degree and we can see something more

 

[PES+]

Just for giggles
Provided the previous owner did not already remove the offending bit or bits, check very closely in the muffler use carb cleaner or fill the muffler half way with kero or diesel and shake it till you hear the rattle Those heavy little gremlins just about never make it out the muffler outlet.

I could be very wrong about the crank but I suspect Lakeside called it on this one

 

[Lakeside53]

I'm not "seeing" any issue with the crank big end. You need to check the balls on the main bearings - pull the oil seals and check the cages/balls.

You do not need to use an acid. Just very carefully grind off any projection from the two dents, then a very gentle hone..

This is what you MIGHT see if your mains are bad:

This one has all its balls, but the cage is collapsed.