Mowing mower deck stalling tractor

[art]

Shear bolt on a mower? I don't think so! The belt would normally slip on many and that's one of the reasons they use a belt drive.

Looking at prior posts it was brought up about shear pins on a snow blower. It was a few years back I was clearing our used lot for an auction with a big three point hitch blower that was shear pin protected. Was going along good when the tractor just died!!
I turned of the po and the tractor started right back up and as I thurned the PTO back on it went to die again so I shut it down and went around to the rear when I see a tire sticking out of the blower. Just like a sweat shirt it would never had a shock to break the pin!!!

 

[leonz]

I can simpathise with you art as my snow pup sucked in 30 feet of 12 guage extension cord for my salamander before it stopped. luckily it cooperated and unwound like it went in:laughing:

 

[studway]

I'm not sure why it makes a difference if the deck or tractor fails, either way it is an expensive failure. Just the parts to repair the deck were over $400. The entire gear box has to be disassembled, there are 3 bevel gears that have to have the depth set, everything is held in place with snap rings and there are only two access openings. It's tight, accurate work, not a quick job and it's not a cheap job if you pay to have it done. Dealers won't stock those parts so you will wait. I've got to imagine the total bill was one of those 'have a seat' moments as I was told it was probably just a bad seal.

Most importantly, my point wasn't to say the deck will fail first. The direction of this thread seemed to be the belt would act as a safety device and I wanted to counter that. Only the outer blades are belt driven, the center blade is direct drive through the gear box. Anything you hit with that blade is transferring shock back to the tractor.

I don't believe (short of an actual safety device) you will find individual components of a drive line seriously over or under engineered, they will all be designed to same specs. IMHO any part in the drive line could fail, don't count on my example as assurance the weak link is in the deck. I merely meant to say that you CAN do serious damage by hitting objects.

Thanks for the clarification. I took a look at my deck today and noticed, as you pointed out, that the middle blade is indeed driven directly from the gear box, meaning that even if the belts did have slip built in like a lot of other mowers and other types of equipment have to protect the gears it wouldn't matter. That sweatshirt I ran over was wrapped around the middle blade.

I know people will disagree with me on this, but I consider this a serious design flaw. This isn't a riding lawn mower or garden tractor it's a 23hp deisel tractor fully capable of doing real farm work. I'm not sure why people think it isn't intended for "commercial" use. There are commercial applications that require a small tractor. If not a BX, what other product would fit the bill? They don't sell Kubota's at Lowes. I bought mine at a place that sells huge constuction vehicles. It may be small, but it's a powerful little tractor that wouldn't make much sense for someone with a perfectly manicured lawn to use for their mowing duties. I'm sure there are many, many people using these to mow less than pristine areas.

As I said earlier, I haven't seen anyone reporting that they blew their engine or gearbox by hitting a stump or rock or running over twine or wire with a BX, so maybe (hopefully) its just been engineered in such a way that the stalling is the failsafe and doesn't cause damage. I've done it about 10 times in 4 years without any problems. Still, it bugs the heck out me that their isn't a safety.

Anybody know if I could put a slip clutch on the mid PTO or coming out of the deck? My box mower has a slip clutch attached to the gear box. Works great. I seem to recall that an old box mower I used a while back had a shear pin built into the drive arm near one end. Could I find a little drive to replace the one that came with the deck that has a shear pin?

 

[TripleR]

Yeah, I think you are right that most people will disagree and I am one of them having used different brands in pretty rough conditions for more years than I can remember with absolutely no damage, I view the design as adequate to the intended use.

If I was that worried about it, which I am not, I would simply back off on the blade bolt torque a bit from the 75-80 foot pounds. I found one of my blades had loosened to the point to where it could be turned by hand, but was still tight enough to give a good cut.

 

[radioman]

I know people will disagree with me on this, but I consider this a serious design flaw. This isn't a riding lawn mower or garden tractor it's a 23hp deisel tractor fully capable of doing real farm work. I'm not sure why people think it isn't intended for "commercial" use. There are commercial applications that require a small tractor. If not a BX, what other product would fit the bill? They don't sell Kubota's at Lowes.

Good point here- they don't sell BX's in box stores.

As I said earlier, I haven't seen anyone reporting that they blew their engine or gearbox by hitting a stump or rock or running over twine or wire with a BX.?

I believe you might be our first. I hope I'm not offending you, but you seems to be out lab rat in this case.

Anybody know if I could put a slip clutch on the mid PTO or coming out of the deck? My box mower has a slip clutch attached to the gear box. Works great. I seem to recall that an old box mower I used a while back had a shear pin built into the drive arm near one end. Could I find a little drive to replace the one that came with the deck that has a shear pin?

This is just a guess here-I don't think there is enough room even for the smallest slip clutch. The problem is when deck is in uppermost position, it looks to be about less then 6 inches of space. Plus your fuel filter is there by the mower shaft.

Only suggestion I have is add your own shear bolt. At this point is take the yoke shaft off your mower deck that connects to the mower gearbox and take it to a machine shop. Have them cut the shaft from the yoke end 4 inches back and weld a tube on the shaft cut off to hold the shaft together to yoke end. drill a hole for a shear bolt in tube and shaft and add shear bolt. Keep in mind that your fuel filter is RIGHT there by the shaft and it will need to be a short shear bolt.

 

[studway]

If I was that worried about it, which I am not, I would simply back off on the blade bolt torque a bit from the 75-80 foot pounds. I found one of my blades had loosened to the point to where it could be turned by hand, but was still tight enough to give a good cut.

That crossed my mind as a possible solution.

 

[studway]

Only suggestion I have is add your own shear bolt. At this point is take the yoke shaft off your mower deck that connects to the mower gearbox and take it to a machine shop. Have them cut the shaft from the yoke end 4 inches back and weld a tube on the shaft cut off to hold the shaft together to yoke end. drill a hole for a shear bolt in tube and shaft and add shear bolt. Keep in mind that your fuel filter is RIGHT there by the shaft and it will need to be a short shear bolt.

I thought about that, but I'd rather not make such a major mod. I like the idea of loosening the blade bolts a bit.

 

[SPYDERLK]

studway- you make many good points as well. With the last post you made, it really has clarified many things for us I would say.

Perhaps when talking with your dealer, you could make a point that the snowthrowers, that the cheapest and most expensive ones have a shear bolt. now go figure. While snowthrower and MMM are different implements, but It just goes to show your point that a expensive purchase should have some sort of a protection. I can't really say don't worry about it since I never stalled the engine via MMM jammed or clogged. I really don't think the gearbox is a protection to the engine.

The difference between MMM and snow thrower drive is infinite. As describe well by TripleR and others there is slip built in to the drive and blade attachment on the mmm. On a snow thrower there is major torque multiplication after the initial drive, whether it be belt ot gear. The only slip possible on a Kub snow thrower is shearing a pin. Even on belt drives the fact that there are tremendous torques available on the torque multiplied slow turning elements forces the use of a protective device in this part of the mechanism.
larry

 

[SPYDERLK]

I thought about that, but I'd rather not make such a major mod. I like the idea of loosening the blade bolts a bit.

I wouldnt do that. They are going to slip either way in shock situations. If you make it so they slip too easily you will end up grinding up the metal at the spindle attachment point. Theres plenty of design strength to accomodate the forces transmitted at correct bolt torque. They surely didnt pick that number out of the air.
larry

 

[czechsonofagun]

I would not loosen up the bolt either. I torque them down and still once a season or so one of them will get loose and the blade will spin freely. Typically after I went over some poison ivy, I believe in the evil spirit of things happening on purpose

That joke out of the way. I too stop the tractor while cutting with my 60" MMM, just clutch and start again, lift the deck and ease the clutch in to see if it works now or if I have to get under. I am sure the between the belt slipping and the robustness of the tractor nothing in the transmission will brake.