Testing A Raisman Platt Crankshaft In An MS660

[Stihl 041S]

Now I'm not trained in failure analysis, nor am I an engineer, just a mug mechanic but it looks like the crack has propagated from around the 2:00 o'clock position from a stress raiser of some sort.

Now it could start as Rudi suggested, or the lead or start of the thread (threads are notorious for this, particularly cut threads if the tool is a little blunt) or just some sort of notch, and grown from there.

As threads get courser, we put a Larger or MORE blunt insert to Prevent the thread from weakening. The root has a larger diameter and the radius makes it stronger.

Just sayin. ;-))

 

[tdi-rick]

As threads get courser, we put a Larger or MORE blunt insert to Prevent the thread from weakening. The root has a larger diameter and the radius makes it stronger.

Just sayin. ;-))

Bigger radius and blunt cutting leading to a torn surface are different though, aren't they ?

eg. a Whitworth threadform is actually preferable to a UNC thread as it's radiused at the root ? (not withstanding the 5* difference)

Maybe I should've said a rough lead ?

 

[barneyrb]

Randy, if'n it makes any difference I've replaced 2 cranks broke in the same place. Different saws and different owners but same end results.......

 

[Stihlman441]

Nice pics,nice work as uauall thanks.

 

[blsnelling]

Very nice work. Clean shop!

 

[Warped5]

What the story with that can of nuts?

Does it follow Jon everywhere; even into the storeroom with the USC?

:confused2:

 

[Philip Wheelock]

...what caused that to shear off?

There have been a number of threads on AS about similar shearing failures on 660's. One explanation would be that the crankshaft thread diameter at the clutch carrier isn't large enough to withstand the bending forces generated by the offset of the rim sprocket from crank bearing inherent in the inboard clutch design, which creates metal fatigue until the crank fails from a combination of rotational shear and bending stresses. Also, cutting the thread in manufacturing could have created small cracks at the bottom of the thread that could have been the starting points of failure. Wonder if the clutch carrier thread diameter will be increased in the 661...

 

[Mastermind]

I don't think the cylinder cover has ever been off this saw,am i seeing things or will a 461 coil bolt to that hole below the coil ?

Bolt up yes. Run just right? I ain't sure........we can find out very soon though. :msp_thumbup:

You have a bunch of cash and time invested in testing AM parts........you ask, I'll do.

Very nice work. Clean shop!

In spots and places. :msp_unsure:

What the story with that can of nuts?

Does it follow Jon everywhere; even into the storeroom with the USC?

:confused2:

I eat the heck out of those Wasabi Peas. We use the cans to keep bolts in for the saws we are working on.......at times there are 4 - 5 different cans like that sitting around.

I'm impressed with some of the comments on what could have caused the crank to fail.....this sort of stuff is way over my head.

All I know is that it's broken.......and that we are fixing that. :msp_unsure:

 

[Dennis Cahoon]

What is the price of the AM crank?

My son brought home a broken crank that looked just like that one. Crummy OEM parts if you ask me!.....Hahahahahaha!

 

[Stihl 041S]

Bigger radius and blunt cutting leading to a torn surface are different though, aren't they ?

eg. a Whitworth threadform is actually preferable to a UNC thread as it's radiused at the root ? (not withstanding the 5* difference)

Maybe I should've said a rough lead ?

I'd worry about proper Heat Treat.

But yes


Rough would make it worse.

The courser the thread the larger the radius allowed.

Are the threads cut do we know?

 

[exSW]

What is the price of the AM crank?

My son brought home a broken crank that looked just like that one. Crummy OEM parts if you ask me!.....Hahahahahaha!

Not so funny,you drop a grand on a saw it ain't supposed to do that....ever!

 

[watsonr]

What is the price of the AM crank?

My son brought home a broken crank that looked just like that one. Crummy OEM parts if you ask me!.....Hahahahahaha!

Come on Dennis... we know that ain't true hahahahha!!!

 

[Mastermind]

What is the price of the AM crank?

My son brought home a broken crank that looked just like that one. Crummy OEM parts if you ask me!.....Hahahahahaha!

I didn't pay for it........it was sent for this test. I'm not sure of the price.

Not so funny,you drop a grand on a saw it ain't supposed to do that....ever!

I wish that were true......but you should see the stuff I've seen. There's no one brand or any certain saw that's immune either.......stuff breaks.

Come on Dennis... we know that ain't true hahahahha!!!

Sup Randy? :msp_thumbup:

 

[watsonr]

I didn't pay for it........it was sent for this test. I'm not sure of the price.



I wish that were true......but you should see the stuff I've seen. There's no one brand or any certain saw that's immune either.......stuff breaks.



Sup Randy? :msp_thumbup:

I know how much that crank cost..Sup Homey?

 

[Dennis Cahoon]

I know how much that crank cost..Sup Homey?

Probably alot less than that broken OEM crank!

 

[barneyrb]

There's no one brand or any certain saw that's immune either.......stuff breaks.

Saws, tractors, anvils, paper machines, etc...............mechanical stuff breaks

 

[Hedgerow]

Saws, tractors, anvils, paper machines, etc...............mechanical stuff breaks

Ok....
Now you've gone to medlin'...
:amazed:

 

[Mastermind]

Ok....
Now you've gone to medlin'...
:amazed:

Naw man....really. I think Jon could break an anvil. :hmm3grin2orange:

 

[Jimmy in NC]

Naw man....really. I think Jon could break an anvil. :hmm3grin2orange:

Tell him there is a free can of chew inside. Bet be has it cracked open in no time.



Jimmy

 

[Scooterbum]

I've seen 2 cranks just like that. I'd tend to think poor heat treating from the discoloration.