MS660 Seizing Up

[pepe_silvia]

I was milling with my 660 this weekend, had finished making about 6 slabs on an 18" x 5' black jack oak, and was about 1/2 way through the second cut into a 18" x 6' post oak, when the saw abruptly stopped. No warning, clattering, smoking, nothing, just full stop.

Tried pulling and she was seized up tight. Talking to a buddy's dad who knows of these sorts of things, he recommended pouring some Marvel Mystery Oil into the cylinder and letting it sit overnight, then popping the top of the cylinder with a dowel to try to loosen it.

After setting overnight, we didn't have a dowel that would fit through the decompression valve, and being that the spark plug isn't at a good angle to hit the top of the cylinder, my buddy was able to tap it free by using the dowel and tapping it on the flywheel fins.

So now the piston was completely free moving, could move the flywheel easily by hand. The flywheel would turn some number of times and it would get stuck again. Tap it free, repeat the process, same result. We gave up for the time being because it was time to leave. I got it home today and tapped it free, and was able to pull on the starter probably 30 times before it decided to seize up again.

I've got probably 2-3 hours on a Wolf Creek Nikasil big bore piston/cylinder. There are no visible scores on it, my limited knowledge tells me that it looks just fine.

Prior to running it this time, I had my saw guy (who might hang out here...) tune it up and put an aftermarket metal flywheel on it. This leads me to believe that the cause is likely somewhere in the flywheel.

I haven't been able to get ahold of my saw guy, so I thought I'd see if anyone here had any ideas.

 

[Guido Salvage]

If it rolls over and then hangs up, I would suspect the bearings.

 

[KYsawman]

I second guido salvage sounds like a crank bearing has gone bad.

 

[Chainsaw Jim]

Did you look through the intake at the piston or only through the exhaust?

 

[bayard]

get a saw mill

 

[pepe_silvia]

If it rolls over and then hangs up, I would suspect the bearings.

Would it happen every cycle, or just intermittently?

Did you look through the intake at the piston or only through the exhaust?

Just through the exhaust.

 

[pepe_silvia]

get a saw mill

Don't discriminate against Alaskans.

 

[Chainsaw Jim]

Just through the exhaust.

You should probably pull the carb and have a peek. It could be melted pretty bad and still be perfect looking on the exhaust side. The back side of the cylinder can have damage below where you can see when peeking through the exhaust side.

 

[Jacob J.]

Would it happen every cycle, or just intermittently?


Just through the exhaust.

Sometimes when a main bearing cage has broken- the roller balls will be free and then after several revolutions- they'll bunch up on one side and stop the movement of the crankshaft. I think Gary called it on the main bearings. I'm guessing when you replaced the top end you didn't split the cases and rebuild the lower end?

 

[pepe_silvia]

Sometimes when a main bearing cage has broken- the roller balls will be free and then after several revolutions- they'll bunch up on one side and stop the movement of the crankshaft. I think Gary called it on the main bearings. I'm guessing when you replaced the top end you didn't split the cases and rebuild the lower end?

I had the top end done by someone else, but no, I don't think he rebuilt the bottom end.

 

[pepe_silvia]

Sometimes when a main bearing cage has broken- the roller balls will be free and then after several revolutions- they'll bunch up on one side and stop the movement of the crankshaft. I think Gary called it on the main bearings. I'm guessing when you replaced the top end you didn't split the cases and rebuild the lower end?

Would I be able to hear anything if the main bearing cage broke?

 

[fordf150]

no. there will be no noise but if you pull the clutch drum and clutch you may be able to get some movement out of it. should be nice and tight, any up and down movement is a bad bearing.

 

[Chainsaw Jim]

If it's the bearings locking it then the crank should wiggle around considerably when it's freed up.

 

[Guido Salvage]

Out of curiosity, what fuel/oil ratio are you using? Milling is the most demanding task for a saw due to the extended duration of the cuts and you are using the entire length of the bar. You need to be running 32:1 and allow the saw to cool between cuts. An auxiliary oiler will help and the chain needs to be kept sharp. Trying to force a saw with a dull chain when milling will cook it. Lastly, the cooling fins need to be free of any buildup to properly dissipate the heat generated.

 

[pepe_silvia]

If it's the bearings locking it then the crank should wiggle around considerably when it's freed up.

I popped off the sprocket and gave it a wiggle and it's really tight. Would the play be there with the clutch still installed?

 

[pepe_silvia]

Out of curiosity, what fuel/oil ratio are you using? Milling is the most demanding task for a saw due to the extended duration of the cuts and you are using the entire length of the bar. You need to be running 32:1 and allow the saw to cool between cuts. An auxiliary oiler will help and the chain needs to be kept sharp. Trying to force a saw with a dull chain when milling will cook it. Lastly, the cooling fins need to be free of any buildup to properly dissipate the heat generated.

It was somewhere in the 30-40 range. I was taking a few minute break between each cut, chain was brand new at the start of the day. It wasn't sparkling clean, but there wasn't a bunch of buildup or anything.

 

[pepe_silvia]

You should probably pull the carb and have a peek. It could be melted pretty bad and still be perfect looking on the exhaust side. The back side of the cylinder can have damage below where you can see when peeking through the exhaust side.

Never pulled the carb on this guy before so I'll have to figure out how to do that.

 

[fordf150]

I popped off the sprocket and gave it a wiggle and it's really tight. Would the play be there with the clutch still installed?

Yes... I just said take clutch off to give you more to grab.

 

[pepe_silvia]

Yes... I just said take clutch off to give you more to grab.

Ok, so that bearing is seemingly solid. What is next?

 

[fearofpavement]

Another possibility is that there is a piece of hardware under the flywheel. (nut, bolt or whatever stuck to the magnet)