Mowing Breaking BX Blade Bolts

[BotaBigot]

My guess is overzealous use of impact wrench at dealer...fatiguing bolts. Have any you subsequently replaced failed?

 

[SPYDERLK]

My guess is overzealous use of impact wrench at dealer...fatiguing bolts. Have any you subsequently replaced failed?

Yes. See original post.

 

[logdog]

My questions is how are you getting the broken bolt out of the spindle, I'd think that would be a *****. Mine does have a hex looking washer thing and I think I have two of the spring washers, but I also have a 60" deck.

I am able to walk them out with a small chisel. Im getting good at it.

 

[logdog]

I have over 600 hrs on my 48" mmm with the original bolts and washers. Have never had a problem and the blades have been removed every 25 - 35 hrs for sharpening. The washers are supposed to be installed with the cupped side toward the blade. Is it possible that one or both of the washers are not installed correctly? Also, is it the same spindle position that the bolt is breaking on? Maybe those washers need replaced.

They are new spring washers. This is the first time I found one after it broke. Usually I cant find the bolt head or washer.

I have had multiple breaks on 2 of 3 blades. The center and shoot side.

This is driving me batty! Like I said, 2 summers with no problems. This is the summer of broken metal!

 

[dodge man]

Go back and read Spyderlk's post. I think he may be on to something. If I follow what he is saying my deck is a 60" deck and my deck has a washer where the inside hole is hex shaped. This goes under the blade. This locks into a hex shape on the end of the spindle. This would help keep the blade bolt from getting any tighter. Yours doesn't have this feature. Think about everytime you start the blades, this may be trying to tighten the bolt until it gets so tight they break.

 

[coveredbridge]

This has me puzzled also. I keep looking at those pics to see if there's any clues to what's happening, and I noticed that the blade seems to have an arc, or bow, between the cutting edges. I know my blades are flat. Are those not OEM blades, or is that an optical illusion? Did you change the type of blade you are using this year and could that be causing the problem?

 

[logdog]

Go back and read Spyderlk's post. I think he may be on to something. If I follow what he is saying my deck is a 60" deck and my deck has a washer where the inside hole is hex shaped. This goes under the blade. This locks into a hex shape on the end of the spindle. This would help keep the blade bolt from getting any tighter. Yours doesn't have this feature. Think about everytime you start the blades, this may be trying to tighten the bolt until it gets so tight they break.

If the missing hex feature is the problem, why were there no issues for 2 years? I will try and get some more pics when I take the deck off

 

[logdog]

This has me puzzled also. I keep looking at those pics to see if there's any clues to what's happening, and I noticed that the blade seems to have an arc, or bow, between the cutting edges. I know my blades are flat. Are those not OEM blades, or is that an optical illusion? Did you change the type of blade you are using this year and could that be causing the problem?

They should be kubota blades. The dealer put them on.

 

[coveredbridge]

The blades on my 48" mmm are flat in the middle. If your blades are bowed in the middle, and they are new blades, that could be causing the problem. You might want to verify that those are the correct blades for your mower.

 

[Tollster]

Typically a bolt does not fail in the thread engagement area unless there is some sort of manufacturing flaw (You may be able to see some sort of flaw present in the piece you had that led to the failure). All threads are under equal tension, and actually stretch when torqued. If there is any hairline cracks in the bottom of the thread, this could have been created from a forging lap of an imperfection in the metal, or during the machining process, it will crack there. I have seen hairline indications on new bolts.
Over torque of a bolt almost always results in failure in the transition area between the head and the shank, not the engagement area.
I would be willing to say you have a bad batch of bolts.

 

[SPYDERLK]

If the missing hex feature is the problem, why were there no issues for 2 years? I will try and get some more pics when I take the deck off

Did you read the post? ... Because something changed when they took off the blades. Maybe they lubricated the spindle threads making the bolt easier to turn. Then every time the blade encounters a sudden resistance and slips a little it drags the easier to turn bolt along with it causing it to tighten. It doesnt take much extra turn on a tight bolt to stretch or break it. These bolts are very hi grade and wont stretch much before they break.
larry

 

[radioman]

I been thinking about this all day. How in the world would a tough blade bolt snap like that? It dawned on my just now an possibility, but I could be wrong. what if the bolt hole in madrel is full of dirt or something hard inside making the bolt stick out a bit more or maybe the bolts were too long bottoming out and that extra torque to compress the washer just right to hold blade. This could result in the twisting/weakening the bolts.

I dunno- its just a theory that could merit a few moments to look into so it can be dismissed.

 

[dodge man]

I have no idea what the problem is, there are a couple of good ideas floating around. I might try and go to another dealer and get three new bolts. Maybe they aren't giving your the right bolts. Maybe they are giving you bolts for a 60" deck and they are different? Maybe they did get a batch of bad bolts? If you go to another dealer the bolts might cure your problem.

 

[SPYDERLK]

I still have to pull the deck back off (I hate doing that) but here are a couple pics of the carnage.
View attachment 331191

The broken bolt shows stretching.

 

[logdog]

Autopsy pictures

 

[logdog]

I should also note the bolts have come from multiple dealers. The first couple came from the selling dealer, one came from the next closest dealer because my selling dealer was out of stock and one came from the dealer by my work since I cant get to the selling dealer during the week.

 

[SPYDERLK]

You need to get the dealer where the problem started and Kubota involved. This problem cannot be unique to your mower, but lurking on all with that design. Kubota will have encountered it.
larry

 

[SPYDERLK]

Autopsy pictures
View attachment 331583

Thats too much stretch for it to be a very hi strength bolt. Id say Gr5/8.8 or less. When mine snapped on tightening there was very little elongation. I figured Gr8/12.9. ... [strange] :confused2: ... I did replace my bolt with a standard 8.8 grade and have had no trouble tho. But then the design of the 54" mower prevents any possibility of further tightening from incremental blade slippage, by use of that hex washer I referred to.
larry

 

[CHDinCT]

Maybe a stupid idea - not familiar with your 48" deck, but can your dealer order you a set of the hex washers to use on your 48"er?

 

[SPYDERLK]

Maybe a stupid idea - not familiar with your 48" deck, but can your dealer order you a set of the hex washers to use on your 48"er?

Wood be good if those spindles have a hex nose for the washer to engage. It doesnt look like it from the picture he just posted.