Stihl 661C. Gotchas? Known Issues?

[leadfarmer]

Andy's 661 Betsy. That's what happened to the piston. Same spot

I think your right Willis

 

[tree monkey]

if you drop a tree on them they will break

 

[sawmikaze]

if you drop a tree on them they will break

Are you sure ?

 

[Trevj1]

Are you sure ?

I'm sure. Got my 461 that way. Put together a good saw out of the better parts of two, used the rest and put a new tank/handle assy on the one I kept. A bargoon!

Still have not got near the 661.

Some o y'all seem to think this is my first time to the dance.
Not so much.
Just wondering if the cutie in the corner has a psycho boyfriend, or any freaky habits I should know about, before I make a move, is all!

 

[Redfin]

Worry about the boyfriend later. Twist the T27 man.

 

[MustangMike]

IIRC, some of the early 661s had problems with the intake boot clogging up, the boot was subsequently revised. That could be the problem, but as others have said, I would pull the muffler after I check for compression just pulling the cord.

Always check simple stuff fist, new plug, fuel filter, air filter and check the decomp valve. All these cheap parts can kill a saw. (If the air filter has only been cleaned, and not replaced, replace it, they reach a point they can't be cleaned).

 

[timbertramp]

Andy's 661 Betsy. That's what happened to the piston. Same spot

I started a thread on this but I’d love to hear a bit more about it. I’m baffled....
Looks to me like the skirt hit the internal intake flange and chunked it. This is the third time I’ve seen this. Twice on one saw, swapped top end and removed flange and been working it as a backup goof results (this saw had a year on it)
Second saw, first time it happened, about a month on it....
Both working flawlessly beforehand.

Not to hijack but any details on “Betsy” ??? Mod, timing, etc?

 

[huskihl]

I started a thread on this but I’d love to hear a bit more about it. I’m baffled....
Looks to me like the skirt hit the internal intake flange and chunked it. This is the third time I’ve seen this. Twice on one saw, swapped top end and removed flange and been working it as a backup goof results (this saw had a year on it)
Second saw, first time it happened, about a month on it....
Both working flawlessly beforehand.

Not to hijack but any details on “Betsy” ??? Mod, timing, etc?

It was the first of 8 or 10 that I ported for @leadfarmer's friend Andy. Supposedly the best running one, his favorite by far. Rodney sent the piston and ported cylinder back to me to get my opinion on it. The only thing we both could come up with was that the piston was dropped at some point in time and and weakened that lower left skirt corner. But now seeing that it has happened to someone else makes me wonder. The 661 has always shown intake skirt wear. Maybe that flange is cooling the skirt so much that it's not expanding and remaining loose in the bore, breaking the skirt. I have no idea

 

[MustangMike]

Or, not cooling it enough, and it expands and touches something. I still think that is what happened to the 461 I put a new piston in.

 

[huskihl]

Or, not cooling it enough, and it expands and touches something. I still think that is what happened to the 461 I put a new piston in.

I'd think it would score before breaking the skirt, given all the scored cylinders we see without broken piston skirts. But I didn't expect to change your mind

 

[MustangMike]

Well, what ever is causing it … I think it is more common on newer saws like the 461 and 661 than on older ones like the 660 and 460.

So that just makes me think it may be related to them trying to meet emissions, but I could be wrong.

 

[huskihl]

Well, what ever is causing it … I think it is more common on newer saws like the 461 and 661 than on older ones like the 660 and 460.

So that just makes me think it may be related to them trying to meet emissions, but I could be wrong.

I agree. There's something in there without enough clearance, or too much.

 

[huskihl]

Well, what ever is causing it … I think it is more common on newer saws like the 461 and 661 than on older ones like the 660 and 460.

So that just makes me think it may be related to them trying to meet emissions, but I could be wrong.

Those two models are the only ones that I've heard of doing it. And those two are the only ones I know of in the Stihl lineup that are nearly identical regarding the piston, cylinder, and crankcase

 

[MustangMike]

I know that when I put the 461 back together, I filed that nipple flush so the piston could not hit it, and it ran fine. That does not mean it was the problem, but better safe than sorry!

 

[timbertramp]

Yeah I have a significant amount of wear in the bottom of the intake port actually appears to be through the chrome....waiting in my hone to see. Also I don’t know what was there before it broke. He had to finish two trees in the strip so he ran it after it let loose. Friend says he’s seen this in several 461’s! I’m removing the “stuffer” from now on. Testing one now but feels like more torque without it.

 

[timbertramp]

Did you have any advance on that saw he had break? Wash looks good and everything was oiled up good so it doesn’t apparat to have been lean also running a max flo and checked for holes, carb throat was super clean so I don’t think it was saw dust.

 

[Wood Doctor]

Parts are just plain expensive for any 661C. For example: $110 for a pull cord housing that does not even include the pull cord, spring, pawls, label, etc. Over $210 for a tank housing, $100 for an outside handle bar, over $110 for the carb, etc. The list goes on and on.

A few early 661C saws sold around here had defective ignition modules that the dealer replaced while under warranty. I also find that repairing a 660 is much easier and far less time consuming.

Quick question: why does the 661C flywheel have two sets of magnets, each at 180 degrees from each other? That caught me by surprise. I'm sure the second one is there for a purpose. Do you suppose Stihl is masterminding a 2-cylinder engine for the future?

 

[huskihl]

Parts are just plain expensive for any 661C. For example: $110 for a pull cord housing that does not even include the pull cord, spring, pawls, label, etc. Over $210 for a tank housing, $100 for an outside handle bar, over $110 for the carb, etc. The list goes on and on.

A few early 661C saws sold around here had defective ignition modules that the dealer replaced while under warranty. I also find that repairing a 660 is much easier and far less time consuming.

Quick question: why does the 661C flywheel have two sets of magnets, each at 180 degrees from each other? That caught me by surprise. I'm sure the second one is there for a purpose. Do you suppose Stihl is masterminding a 2-cylinder engine for the future?

One set of magnets provides spark while the other runs the mtronic

 

[MustangMike]

Friend says he’s seen this in several 461’s! I’m removing the “stuffer” from now on. Testing one now but feels like more torque without it.

Removing that bridge is the last thing I would do, as it is designed to help cool the piston. I would open the muffler a bit and remove the limiters and I think you will be fine.

 

[Wood Doctor]

One set of magnets provides spark while the other runs the mtronic.

Interesting. So that is perhaps why the IM (or the flywheel) on the 661C might be overworked and why it often failed during early production? Two possibilities for failure rather than just one.

I then have to wonder what would happen if a 661C flywheel were installed on a 660. I doubt that would work either and I am sure you would all agree. No compatibility anywhere that I see.