Did this MS 660 Crank Get Too Hot?

[Threewood]

Or maybe a better title would be "I found an MS 660 power head in a trash heap that needs new rotating assembly and bearings."

Piston looks unscathed but the rod was bound up on the crank. Straight gassed?


I have the rest of the big parts cleaned and drying. The saw is in great shape.

 

[Skavenger]

It did get hot yes. My best guess is that the temper is gone.

 

[Threewood]

I have a new Stihl crank and bearings on the way! This will be a cheap saw lol.

 

[Skavenger]

It's not every day someone finds there dream saw in the trash. Nice find I would have to say this belongs in the you suck thread.

 

[Thommo]

I had this happen to a cart motor back in my younger days and was told it was from having the low speed mixture set too lean.

 

[Hand Splitter]

What did a 660 crank run you?

I couldn't find a crank for my 441 for less than $350 when I need one!

 

[Threewood]

It was a good, used crank off eBay for $99. I thought about a new chinesium one but figured a parted out Stihl crank is still better.

 

[mdavlee]

Did you look the bearing over in the big end? If the rollers aren’t discolored that color on the rod is from the heat treating.

 

[Threewood]

Did you look the bearing over in the big end? If the rollers aren’t discolored that color on the rod is from the heat treating.

I didn't inspect it visually. The rod to crank bearing was very tight and the two crank bearings were very notch so I figured they needed replaced

 

[Threewood]

There is also scaring inside the crankcase to indicate a clearance issue, possibly from it getting hot.

 

[crabby cooter]

the piston will score long before the crank gives up on straight gas

 

[Jasonrkba]

I need to start looking at peoples trash cans a little better. What a find!

 

[Threewood]

the piston will score long before the crank gives up on straight gas

So as the poster above said....low speed mixture too lean? It wouldn't pull over as is. The rod was pretty tight on the crank and the crank bearings were very notchy. The jug and piston look mint. Plus the scoring inside the crankcase from the rotating assembly making contact.

 

[crabby cooter]

poor oil, lean gas oil mix, would be my guess from what I can see

 

[mobilemech13]

The scaring in the crankcase maybe from the crank not being centered in the case, 660 cranks have to be centered, the bearings are not pressed to zero on crank, crank will rub and piston will not be lined up in cylinder.

 

[Deleted member 135597]

The scaring in the crankcase maybe from the crank not being centered in the case, 660 cranks have to be centered, the bearings are not pressed to zero on crank, crank will rub and piston will not be lined up in cylinder.

Huh? Look where the scarring is. It’s on the bottom. Bad bearings. Now what happened first is the million dollar question. Did the bearing fail first and cause the crank to overheat or did the lack of oil cause the crank to overheat and bearing to fail.

 

[crabby cooter]

the scoring in the case was caused from the rod rubbing it when the bearing failed.


is the saw stock or ported?

side loading could be the cause, but rare in stock saws. if there is a lot of wear on one side of the of the piston or the pin bosses inside the piston, it's likely the cause.

 

[SmellyPirateHooker]

View attachment 688831 View attachment 688832

Or maybe a better title would be "I found an MS 660 power head in a trash heap that needs new rotating assembly and bearings."

Piston looks unscathed but the rod was bound up on the crank. Straight gassed?
View attachment 688839 View attachment 688840

I have the rest of the big parts cleaned and drying. The saw is in great shape.

See the heat line on the rod? If factory stihl rod don't have the bluing id replace the whole crank assembly. The metal properties have been changed and it is now unevenly hardened.

 

[crabby cooter]

See the heat line on the rod? If factory stihl rod don't have the bluing id replace the whole crank assembly. The metal properties have been changed and it is now unevenly hardened.

that a given since the rod a crank pin were destroyed when the rod bearing completely failed.

 

[crabby cooter]

is it a oem or aftermarket crank?

I strongly recommend an oem crank