Mowing Breaking BX Blade Bolts

[Tollster]

They did neck down considerably. If it isn't a manufacturing flaw, it could be the friction washers, typically bolts will not neck down that far with a flaw in it. The bolts necking down shows it did its job within the tolerances it was designed to meet.
I believe some elasticity is needed in the material to over come the transfer shock when hitting something, which is what the two cup washers (Friction washers) are for on my 60", They are designed to slip if you hit something when properly torqued. If they have been over torqued in the past, they tend to flatten out, they will not function as designed and transfer the load to the bolt, resulting in failure.
If you insist on reusing the cupped washers, be sure to clean them up good and spray some WD40 on them and WIPE it off(for proper torque), then torque the blades in increments of 3 until the desired torque is reached. Be sure to install them correctly.

 

[JCByrd24]

I can't tell from the pics, but it looks as though the hole through the blade is larger than the bolt (hole through the washer). Is the spindle stepped to fit the blade hole and keep it centered or is there some other method of keeping it centered, or did they potentially put the wrong blades on.

Custom hardware ticks me off anyway so I would try using a standard HW store bolt instead of a kubota special large head bolt, chances are there was a big bad batch of those distributed to dealers all over.

 

[Scooby074]

The more I think about the more of a headscratcher it is. Im starting to wonder if indeed it was a bad batch of bolts.

Id try finding another bolt that fits, like a class 10.9 allen head bolt and try that for a while.

 

[Jeff H]

I wonder if when the blades were sharpened they are enough out of balance to be causing some wobble that is working on the bolt at high rpm.

 

[Coyote machine]

Here are the facts as presented by the OP. Wife took deck to dealer to have blades sharpened. Soon after this bolts started breaking an so on. I would suspect a low skilled 'mechanic' was given the simple job of removing and sharpening the blades and did so using an impact wrench to do so. When he reinstalled the sharpened blades he might have oiled the bolt threads or sprayed something like WD-40 into the spindle holes, and then used the impact wrench set to whatever '/lbs to slam the blades nice and tight. Wife used mower, blade bolt broke. Then another later. This is clearly a dealer related problem and needs to go back to the place that first touched it and sharpened the blades. By possibly overtorquing with an impact, they could have damaged the spindle holes and no bolt, new or used will fix the problem.
Even if someone used oil or antiseize on the bolt threads, or spindle holes and hand torqued the bolts they would still have overtightened them. Bolts- unless specked to be torqued 'wet' are torqued dry so as to NOT overtighten them.
Take it to your dealer who worked on it and let them fix it until it's right. Unfortunately a lot of shops hire cheap, no nothing summer labor to do 'simple' tasks like sharpening blades- BUT the task is obviously not as simple as some might like to think - it takes skill and presents risk of liability to the shop.
Mention your concerns about injury and that they worked on it last, and never having had a problem until they worked on the blades and see what they say.
Do NOT use the mower until it is proven to work to your satisfaction by the dealer.

 

[Shutesbury]

There was mention that the blades look bowed in the photo.
If they do in person also, would that be an indication of the overtightening that many suspect?

Paul

 

[SPYDERLK]

May look strange, but that is the normal shape for the blades.

 

[craigbaill]

Ok...it may be a longshot buuuut. Did they give you YOUR blades back??? It has been known to happen that blades, chains, etc get mixed up. It would explain why all the bolts keep breaking. Maybe?

 

[Scooby074]

May look strange, but that is the normal shape for the blades.

Yes, they are almost "gull winged".

 

[94BULLITT]

Even though you have a Snap on torque wrench check it with another know good Snap on torque wrench to be sure it is accurate.

What are you torquing them too?