Ms661 falling while in the cut

[Matt Schmitt]

I have a 661 that while I was cutting seemed to bog In the cut. I’ve read where guys have had electrical issues but I think mine is the piston/cylinder. I put a compression test on it and it was right around 130 which is low but how low can these go reliable, starts and revs fine but doesn’t seem strong while cutting. I did take the cylinder off and piston I have some pics tell me if you think top end is my issue or not. Piston pic is exhaust side as well as the cylinder where u see two lines is exhaust side. There not really deep at all if it’s the top end would you do cylinder along with piston or just the piston? And are there any off brands that work well vs oem parts.

 

[grizz55chev]

130 is a little low, put some Caber rings in it, scotch brite the cylinder and piston, get back to work.

 

[Matt Schmitt]

Do you think that’s the issue with its lack of power?

 

[grizz55chev]

Could be, only way to know is put the rings in and run it. Cabers run about $20, worth a shot.

 

[Matt Schmitt]

Are the caber any different than OEM rings I’m assuming they’re better quality but size wise are they the same width?

 

[grizz55chev]

Are the caber any different than OEM rings I’m assuming they’re better quality but size wise are they the same width?

I believe Cabers are as good and in some cases better than OEM, the size is correct. There’s a post somewhere that states what the ring endgap should be, off the top of my head, I think it’s in the .010 to .008 range, but don’t quote me. Your piston and cylinder look to be in decent shape, just need a little cleanup.

 

[Matt Schmitt]

I did a little surface rubbing on them you can still kind of see the grooves on the exhaust side up top but I can’t feel them at all I’ll take a pic when I get home and repost it.My other Worry is the Nick a cell being worn down too much is that a possibility or would you notice it being warm too much? On a four wheeler of mine you could see a way of where the nickel still had worn away I don’t see that on this.

 

[Matt Schmitt]

Since clean up

 

[holeycow]

Keep scrubbing. The crosshatch has to be revealed.

 

[huskihl]

Take the rings off the piston and insert them in the bore 1 at a time. Using the piston to keep it square, push them slightly above the exhaust and measure the end gap.

Either way, the exhaust side of the piston is a little bit scored and could be keeping the rings from sealing to the cylinder wall. A new meteor piston comes with Caber rings, but make sure it's installed correctly. On the early 661 meteors, the arrow pointed the wrong way, which put a ring gap right on the exhaust port.

That cylinder looks to have some hours on it. You're not going to find any crosshatch unless you create your own

 

[grizz55chev]

Take the rings off the piston and insert them in the bore 1 at a time. Using the piston to keep it square, push them slightly above the exhaust and measure the end gap.

Either way, the exhaust side of the piston is a little bit scored and could be keeping the rings from sealing to the cylinder wall. A new meteor piston comes with Caber rings, but make sure it's installed correctly. On the early 661 meteors, the arrow pointed the wrong way, which put a ring gap right on the exhaust port.

That cylinder looks to have some hours on it. You're not going to find any crosshatch unless you create your own

Which is hard to do on nikasil.

 

[huskihl]

How old is the saw? The early mtronic models had coils that caused the saw to run lean. I believe the 4700 coils were problematic. 4701 and later are better

 

[huskihl]

Which is hard to do on nikasil.

80 grit will barely make any sort of scratch in it. I'm not certain it's necessary anyway

 

[grizz55chev]

My personal experience is clean it up till you can’t catch a finger nail, I might go a little better and run my bare thumb over the spot to make sure it’s as smooth as I can get it. No need to hone it, in fact it’s not recommended.

 

[Matt Schmitt]

It does have the 4700 coil. I was going to change it to the 01 is there anything you have to do or just plug the new one in? I ended up ordering a meteor cylinder and piston kit. I’m going to keep this one as a back up. It wasn’t hard the get the cylinder off but I’d rather spend a few bucks and put it back together once and be done. I’m not positive on the model year I was going to send stihl the numbers to find out. Unless one of you guys can tell off the numbers. Also it’s clean to the touch of a fingernail can’t feel and groove but I found a kit for cheap so I’m going to try it out.

 

[huskihl]

It does have the 4700 coil. I was going to change it to the 01 is there anything you have to do or just plug the new one in? I ended up ordering a meteor cylinder and piston kit. I’m going to keep this one as a back up. It wasn’t hard the get the cylinder off but I’d rather spend a few bucks and put it back together once and be done. I’m not positive on the model year I was going to send stihl the numbers to find out. Unless one of you guys can tell off the numbers. Also it’s clean to the touch of a fingernail can’t feel and groove but I found a kit for cheap so I’m going to try it out.

Unless meteor has improved the 661 cylinders, I doubt you'll be happy with performance. I was given one to try and it ran at about 70% as well as oem. I'd run your oem cylinder with the meteor piston.
I've heard the coil problem was a recall/free replacement thing. Can't hurt to ask your dealer about a recall and see if they'll do it

 

[grizz55chev]

Do a pressure vac test to make sure you’re lower end is sealed.

 

[Matt Schmitt]

Wonder why the performance would be less if it’s the same size cylinder. And I’ll check with them on the coil thanks. All cleaned up and waiting for whatever I can figure out what’s best to put back in lol.

 

[Matt Schmitt]

Would it be best to just buy a whole oem top end my dealer quoted me 282 for cylinder and piston?

 

[grizz55chev]

Wonder why the performance would be less if it’s the same size cylinder. And I’ll check with them on the coil thanks. All cleaned up and waiting for whatever I can figure out what’s best to put back in lol.

Performance is related to port timing, from what I’ve read. Your old cylinder is more than likely still your best bet.