Craftsman ZTS 7000 - we have such a problem!

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  #1  
Old 08-09-15, 09:23 AM
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Craftsman ZTS 7000 - we have such a problem!

We have a craftsman zts 7000 zero-turn mower. It is about 5 years old. About a month ago the left blade simply sheared off, leaving part of the bolt in the spindle. We have 6 acres that we keep mowed down, no stumps, no tall grass, nothing that you could run over. Because the bolt sheared off inside the spindle, we had to order the entire spindle assembly, PLUS the pulley on top because it is all attached. In other words, from top to bottom from the blade to the pulley. It cost us nearly $200 to buy every bolt, ring, spacer, spindle, pulley, etc. Now, this particular model of mower does not have a "star" on the spindle to insert the blade like most mowers do. Sears says it is just not built with one. We took the other side blade off and sure enough, that side is not that way and we have never had any trouble with that side coming off or shearing off. So we got the parts and put the mower back together. Mowed for about an hour and ... bamb, it sheared off exactly the same way. We started thinking maybe the bolts were defective. Contacted Sears and they were nice enough to send us the complete repair parts at no charge. Well, we got the parts, took it apart again and put it together again. Yesterday was the first time we used the mower since repairing it. It mowed for about an hour and bamb... seared off again exactly the same way. It makes no noise and simply (blade and bolt) drop to the ground. You don't even know it happens until you see your cut pattern. We are just going to trash the mower, but, we just can't understand why it is doing that. Anybody have any idea what might be going on?? Thank you.
 
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  #2  
Old 08-09-15, 11:10 AM
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The first thing that comes to mind is the bolt shearing as in breaking or is the blade a little loose and literally cutting through the bolt? The bolt half dropping to the ground should show that type of wear.

Secondly would be the bolt being over torqued for the quality of bolt - keeping in mind a bolt of 3/4 inch diameter of grade 8 hardness should handle a lot of torque. What size and thread type (coarse or fine) is the bolt?

Lastly, are you reusing the blade or have you tried a new one?
 
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Old 08-09-15, 11:23 AM
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Were you using the same mower blade each time the bolt sheered? If so I would get a new blade, check it for balance and see if the problem goes away. Balance (or lack of) and spinning blade at certain rpm's can sometimes do bad things to metal surprisingly quickly.

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I had an airplane with a fixed pitch aluminum propeller that resonated when turned at a specific rpm. The vibrations created can break the end of the engine's crank shaft where the propeller is mounted. I could turn it faster or slower without problem but could never let it stabilize on that evil rpm unless I wanted to try the big red canopy jettison handle and parachute.
 
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Old 08-09-15, 12:20 PM
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Both good suggestions. It sounds like the bolt is tightening while it's running. You've replaced the parts 3 times now and the same thing happens... what parts are common to all 3 failures? Are the bell washers in place? Are they still belled? Are they turned with the concave side toward the blade? You may need to replace them if they aren't providing the friction needed to keep the blade solidly mounted to the big flat on the end of the jackshaft.
 
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Old 08-09-15, 01:22 PM
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Another thing that come to mind in terms of Cheese mentioning it tightening on the go is whether the end of the jackshaft is clean, dry and square ended. If the bolt head side is being held and the shaft end doesn't have a good grip on the blade the shaft torque would try to continually tighten the bolt since the bolts threads would be reverse threads.
 
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