We are completed stumped!

[motoman]

The responders in this thread are on the right track IMO. We do need closeup pics of the sheared bolt halves. Are there any circular marks on the blade clamp area which might indicate looseness which could lead to over heat and annealling (softening) of the bolt? Any purple or brow color on the blade in that area? Or overheating and shock hardening (embrittling) of the bold on cool down or perhaps water is being used to clean the deck and "quenches" an over heated bolt? If the bolts being furnished are a bit long or somehow the new bolt housing is under bored (depth) you could be torquing against this abutment when you think you are properly stretching the bolt. Try making some depth measurements with a caliper vs length measurement of the old and new bolts. And , though doubtful if the bolts are OEM, there have been many bootlegged low tensile bolts smuggled into to this country . Legititmate bolt head markings can be found that will identify the factory and also the grade.

Perhaps more info than you wanted??:laughing:

Buy a blue marker pen and take a reading of the bolt bearing surface after torquing . Both it and its mating surface should show contact. Do this also to the tip of the bolt.

Kept thinking ...if you use a lubricant like anti seize and do not reduce the required torque by up to 40% you could be causing the bolt to yield (stretch too far). There is a chart in this forum showing the lubricants and reduction factors.

 

[RoperGuy]

If you still have your old spindle assembly, you should try too drill out the stud and threads, use a tap and cut threads for the next size up bolt, go to a place like fastenal or brafasco and get your self a higher grade bolt. It's a free test anyways.

 

[Homer1]

As for pictures, try to sign up for a free Photobucket account or similar, then upload your pictures there, and you can link the pictures here on the forum for us to see. You can use the "img" link and paste it directly into a post once hosted, and it should just pop up as a picture here. If not, you will still be pasting a link that we can click on to see it.

Really an odd problem, I'm sure we'd all like to see you get it figured out fast!

 

[Rock1956]

<iframe width="480" height="360" src="http://s989.photobucket.com/user/lisa_carnell1/embed/slideshow/"></iframe>

see if this works for the pictures

 

[Rock1956]

As for pictures, try to sign up for a free Photobucket account or similar, then upload your pictures there, and you can link the pictures here on the forum for us to see. You can use the "img" link and paste it directly into a post once hosted, and it should just pop up as a picture here. If not, you will still be pasting a link that we can click on to see it.

Really an odd problem, I'm sure we'd all like to see you get it figured out fast!

lisa_carnell1's Library | Photobucket

 

[logan01]

The only reasonable problem I can come up with is, assuming the bolts are good, is that you are torqueing them too tightly. Are you using an impact wrench? If so, do you have an idea as to lbs? For grins, I would find a way to remove one of the broken bolts, cleanup the bottom of the spindle, purchase a grade 8 or stronger bolt. If possible, even if it requires cutting, I would use a bolt that is a solid 1/8" shorter than the factory bolt just in case the factory length, for whatever reason, is bottom out thus putting stress somewhere along the bolt. Instead of cutting, you might be able to use a washer or two on the outside of the blade.

 

[motoman]

Picture suggests work hardening or over torque IMO. (Looseness and repeated bending or torquing beyond the yield point. ) The pictures help, but even the picture of the head portion break- off would help also (the other half). I'm guessing lubricant and unlubricated torquing force or air wrench and lubricant and just tightening by judgement (over torque). But if all 3 were treated similarly it is a puzzle.:2cents:

 

[DaveTN]

Someone earlier mentioned swapping out the other spindle/pulley assembly and
see if it wrings the bolt in two on that one. If so, then it would have to be something
only on that one side of the deck causing the bolt to shear or wring in two pieces. If
the bolt is a high enough grade to resist shearing, then it has to be something in the
torque being too much, or something misaligned causing the shear force. I might try
swapping out one from the other side of the deck to see if it wrings in two or not; But
I would hate to see it shear that one as well. Odd that it only affects that one side.
Also it is shearing down in the shaft and not just the top portion at the top of the pullsy.
I have seen shafts wring off at the blade but this is not the case either. :confused2:

 

[mechanic mark]

Purchase a left handed cobalt or titanium drill bit to remove broken bolts, after locking bit in chuck place drill in reverse, drill slowly & spray bit with oil every minute or two to keep bit cooled down. Purchase two grade 8 bolts of same size to fit, purchase a small pack of antiseize compound & put on bolt threads, torque bolts with torque wrench to specs., grease spindles.

 

[bertsmobile1]

With the Metalurgists hat on and allowing for the quality of the images, that looks pretty much like a strait torsional brittle shear fracture.

So as per previous posts, try some grade 8 or better bolts.
Measure the depth of the bolt hole very carefully.
I have a sneaky suspicion that your spindle hole might be a bit too shallow or the spindle blade assembly is missing a spacer so the bolt is bottoming out in the hole.
The act of mowing tightens up the spindle bolt and my guess is your bolt is bottomed out then gets more torque from the blades so snap.
Specified torques are always for a clean dry thread unless otherwise instructed.
Lubrication can cause drastic over tightening.
If both the top nut & bottom bolt were lubricated then you can be drastically over tightening the whole system.