Stihl MS 192 C- I Think I Broke Something

[Toneman]

Was changing the spur sprocket on my MS 192 C and didn't have a small diameter plastic piston stop so I used the old rope in the cylinder trick. Got the sprocket changed over, but now the crank spins, but the piston doesn't move. Is it possible that I broke the connecting rod? I didn't use any air tools, just a wrench and the sprocket came apart easy.
Will take it apart on the weekend and see what is going on.

 

[Mastermind]

Yep, they have a stamped rod....and you bent or broke it.

 

[Andyshine77]

You likely broke the rod, or the wrist pin crushed the underside of the piston and broke free. Sounds like they have the same weak rod and piston like the 170.

 

[Mastermind]

You likely broke the rod, or the wrist pin crushed the underside of the piston and broke free. Sounds like they have the same weak rod and piston like the 170.

They share the same crankshaft Andre.

 

[stihl sawing]

A stamped piston rod? How do they get away with such cheap crap.

 

[Mastermind]

A stamped piston rod? How do they get away with such cheap crap.

It's great......it's a Stihl.

 

[XSKIER]

They share the same crankshaft Andre.

How's that? Is not the MS 170 the dreaded inboard clutch? Is not the MS 192 T C-E the highly praised outboard clutch? Would not the PTO ends of those crankshafts be different?

 

[nmurph]

Maybe Brad won't get too upset if I drag this one up-

http://www.arboristsite.com/chainsaw/81365.htm

 

[Mastermind]

How's that? Is not the MS 170 the dreaded inboard clutch? Is not the MS 192 T C-E the highly praised outboard clutch? Would not the PTO ends of those crankshafts be different?

I might be thinking about the 019......191, 192 something like that.

Checking Media Cat..... BRB

 

[Mastermind]

Yep,

017, MS170, 019T, 190T all share same crank....

Checking 192 now.

 

[Mastermind]

The 191 shares the cranks with the MS180, 018.

The 192 is different as you said.

Thanks for straightening me up there.

 

[mountainlake]

Stihl quality, are you listening Stihl? Steve

 

[Toneman]

Really disapointing that Stihl would use such a cheap material for the con rod.. This saw retails at $400.00 here in Ontario.
Will take it apart tomorrow.

 

[Saw Dr.]

Hey guys, I have NEVER heard of a 192, 170, 180 or any of the other rods failing under USE. They all seem to fail when being worked on...... The 192 comes with the piston stop just to prevent this. If the dealer did not supply one, they did you wrong.

I realize that one should be able to take the sprocket off, but that is why they supply you with the tool. The rope thing has been argued to death here. The rope trick has been used in my shop many times, but it is a calculated risk. I agree that the stamped rods seem flimsy, but I have not seen one fail yet under normal use. Lots of mechanical things require special tools to do maintenance. Often the penalty for using makeshift tools is damage and wasted $ and time. This is not restricted to saws. If the O.P. had used the factory piston stop, this thread would not be here.

 

[naturelover]

+1

Probably best if using the rope method would be to place the cylinder as close to TDC as possible.




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[Philip Wheelock]

...Probably best if using the rope method would be to place the cylinder as close to TDC as possible.

Theoretically, stopping the piston so that the connecting rod journal is minus 90º from TDC would provide the greatest torque resistance at the crankshaft for the least axial load on the connecting rod.

 

[mountainlake]

+1

Probably best if using the rope method would be to place the cylinder as close to TDC as possible.




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TDC would put the most stress on the rod, middle of the stroke would be best. Steve

 

[naturelover]

Wouldn't that make it easier to bend?

Seems TDC would put all the force straight down through the rod instead of a twisting moment at 90?


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[Andyshine77]

TDC would put the most stress on the rod, middle of the stroke would be best. Steve

Incorrect. Think of it like a a 1x1 piece of wood, it's compression strength is many times greater, than side load strength. No it's not really the same thing, but it's the same basic idea.

 

[Philip Wheelock]

TDC would put the most stress on the rod, middle of the stroke would be best. Steve

Incorrect. Think of it like a a 1x1 piece of wood, it's compression strength is many times greater, than side load strength. No it's not really the same thing, but it's the same basic idea.

It's important to get this right. mountainlake is correct. As a structural analysis, assume a connecting rod journal offset from the crankshaft centerline of 1", and that we're applying 40 ft/lbs of rotational force at the clutch. At 90º BTDC the 1" horizontal offset from the crank centerline results in 480 lbs of axial force (40 lbs x 12"/ft) at the connecting rod, which, due to pin connections at each end, never sees side loads. When the conrod journal is 10º BTDC, the horizontal offset from the crank centerline is TAN 10º x 1" = 0.176". The resulting axial load on the conrod is 2722 lbs (40 lbs x 12"/0.176"/ft), making it much more prone to buckling.