Question about PTO Operation

[kpbeddin]

Hey guys,
I found the shear pin on my rotary mower broke as soon as I finished mowing a couple of weeks ago. I had not hit anything but I had just made the dumb mistake of turning the ignition key instead of the PTO switch when I was ready to stop the mower. It occurred to me that the PTO shaft must have stopped abruptly once the engine shut down and caused the sheer pin to snap. I'm not sure this is the reason, but if it is, it seems like a fairly unforgiving design. Anyway, no harm done and lesson learned, but hopefully this knowledge will save someone some unnecessary grief and downtime.

 

[MikeInEburg]

Sounds to me like the shear pin did it's job! If it hadn't sheared, think what may have happened to your driveline...
Mike

 

[kpbeddin]

Sounds to me like the shear pin did it's job! If it hadn't sheared, think what may have happened to your driveline...
Mike

Yes, absolutely and I am not blaming the shear pin; however, my point was that on a tractor with a manually engaged PTO, the PTO will normally coast down if the engine stops for any reason. This doesn't appear to be the case here.

 

[LittleBlueTractor]

Yes, absolutely and I am not blaming the shear pin; however, my point was that on a tractor with a manually engaged PTO, the PTO will normally coast down if the engine stops for any reason. This doesn't appear to be the case here.

The PTO on my S3010 is of the "live" variety and I've always assumed it would freewheel if the engine dies for some reason. It's hard for me to imagine why they would design a PTO to work in any other way these days, but there may be some reason I'm unaware of. I'm wondering if maybe there's a brake involved in your "independent/manual" PTO system that mine doesn't have. I got that idea from here:

Power Take Off School

In any case, I'm not likely to test my theory by shutting down with the PTO engaged just to find out. Thanks for posting about this.

 

[rocknrod]

Yes, absolutely and I am not blaming the shear pin; however, my point was that on a tractor with a manually engaged PTO, the PTO will normally coast down if the engine stops for any reason. This doesn't appear to be the case here.

Think about what you did for a moment.
The engine and PTO drive train is cooking along at 24 or 2500 RPM Engaged.
You stop everything by turning off the key - Engine engaged to the PTO.
Your were expecting something different to happen?
That is an Abnormal Operation for any tractor.
Normally - It does coast down.

 

[kpbeddin]

Think about what you did for a moment.
The engine and PTO drive train is cooking along at 24 or 2500 RPM Engaged.
You stop everything by turning off the key - Engine engaged to the PTO.
Your were expecting something different to happen?
That is an Abnormal Operation for any tractor.
Normally - It does coast down.

Actually, I had slowed the RPMs way down because I was (so I thought) about to disengage the PTO. There may have been some coast down had the engine died for another reason (loss of fuel for example) since the switch would still be on. I don't know, I just thought this was worth posting because seeing as we are all human, something similar could happen to anyone under the right set of circumstances.

 

[Localmotion]

Actually, I had slowed the RPMs way down because I was (so I thought) about to disengage the PTO. There may have been some coast down had the engine died for another reason (loss of fuel for example) since the switch would still be on. I don't know, I just thought this was worth posting because seeing as we are all human, something similar could happen to anyone under the right set of circumstances.

I totally agree with your last sentiment Bedding :thumbsup:

While it is logical that the PTO should always disengaged before shutting off the engine, and the other posts in this thread are also right that that is one of the reasons a shear pin is fitted - it never hurts to remind ourselves of the consequences of cutting corners

Any machine (tractors included) are only as good as their operator - hence why shear pins and the like were invented!!!! :laughing:

 

[beenthere]

I wouldn't worry about it, as said the shear pin worked as it should.
But I also wouldn't jump to the conclusions that shutting off the tractor did the number on the shear pin (happened one time? ). It may have been border-line ready to fail.

Some tractors have a free-spin clutch to stop the rotary cutter on the PTO from 'pushing' back through the transmission. This tractor apparently doesn't.

 

[LittleBlueTractor]

Think about what you did for a moment.
The engine and PTO drive train is cooking along at 24 or 2500 RPM Engaged.
You stop everything by turning off the key - Engine engaged to the PTO.
Your were expecting something different to happen?
That is an Abnormal Operation for any tractor.
Normally - It does coast down.

Hey Rod,

I'm still wondering why it wouldn't be designed to just freewheel like a bicycle -- no matter how fast you are pedaling, when you stop, the driving wheel freewheels. That's very old technology and I cannot think of any reason for it to do otherwise on a modern PTO shaft. As the PTO never changes is rotational direction, what reason could there be for it to remain engaged when the driving force stops? I'm not necessarily expecting you to answer this question, but if there is anybody out there that can ....

I really don't like to think it's simply the cost involved unless the expense would be pretty substantial. I just don't think that could be it. Frankly, I'm hoping there's another explanation.

 

[beenthere]

Littleblue
Cost is involved.
The older gear tractors had direct drive PTO out of the tranny. Some of the "new" tractors have that same technology. And cost is involved, or people wouldn't buy the tractors that they do.

 

[LittleBlueTractor]

Littleblue
Cost is involved.
The older gear tractors had direct drive PTO out of the tranny. Some of the "new" tractors have that same technology. And cost is involved, or people wouldn't buy the tractors that they do.

Well as I bought one of the least expensive brands on the market, I guess I shouldn't be surprised if my "value" model doesn't have the latest technology out there.

Are you saying this is a "color" thing and that higher end tractors do have a freewheeling PTO shaft?

 

[bluechip]

Typically, lower end tractors and then those with HST transmissions still have "overrunning clutches" built in, this is why on those tractors you hear a ratcheting sound if you stop the tractor with the pto spinning an implement. The S3010 has a 2 stage clutch, the PTO will freewheel if you disegage the clutch by stepping all the way down. otherwise it is connected to the engine flywheel. No big deal to shear a shear bolt, thats why they are there. Highest level is "independent" PTO meaning the PTO clutch is engaged totally separate from the drive clutch, often by solenoid controlled hydraluic clutch. On these tractors you can start and stop PT0 independently of main clutch. ON 2 stage clutch, you have to release drive clutch before you can release PTO clutch by pushing clutch further down.

 

[beenthere]

.............Are you saying this is a "color" thing and that higher end tractors do have a freewheeling PTO shaft?

I tried not to say that, and forgive me if I implied it.

 

[kpbeddin]

Typically, lower end tractors and then those with HST transmissions still have "overrunning clutches" built in, this is why on those tractors you hear a ratcheting sound if you stop the tractor with the pto spinning an implement. The S3010 has a 2 stage clutch, the PTO will freewheel if you disegage the clutch by stepping all the way down. otherwise it is connected to the engine flywheel. No big deal to shear a shear bolt, thats why they are there. Highest level is "independent" PTO meaning the PTO clutch is engaged totally separate from the drive clutch, often by solenoid controlled hydraluic clutch. On these tractors you can start and stop PT0 independently of main clutch. ON 2 stage clutch, you have to release drive clutch before you can release PTO clutch by pushing clutch further down.

Blue Chip, thanks for the informative write-up. I have an i3030 which has the independent PTO. Is this type of PTO suppose to remain engaged if the engine inadvertently shuts down?

 

[LittleBlueTractor]

Typically, lower end tractors and then those with HST transmissions still have "overrunning clutches" built in, this is why on those tractors you hear a ratcheting sound if you stop the tractor with the pto spinning an implement. The S3010 has a 2 stage clutch, the PTO will freewheel if you disegage the clutch by stepping all the way down. otherwise it is connected to the engine flywheel. No big deal to shear a shear bolt, thats why they are there. Highest level is "independent" PTO meaning the PTO clutch is engaged totally separate from the drive clutch, often by solenoid controlled hydraluic clutch. On these tractors you can start and stop PT0 independently of main clutch. ON 2 stage clutch, you have to release drive clutch before you can release PTO clutch by pushing clutch further down.

Thanks for taking the time to go into this. I've probably done about 15 hours of brushing hogging with my S3010 and pretty much have the 2-stage clutch stuff down now -- change gears and direction all the time without interfering with the PTO speed.

So here's my question: Suppose I have the transmission in neutral with the PTO engaged and running my cutter at 540 RPM. Could I cause any damage to anything if I were to then quickly push the throttle down to idle. That's not as extreme as killing the engine with the switch, but the engine should drop speed much quicker than the cutter. I'm not trying to beat a dead horse here -- just wanting to throughly understand.

 

[Gary Fowler]

Guys for about $20 you can "upgrade" to freewheeling on the PTO regardless of what stupid thing you do accidently or on purpose. Just get the little freewheeling pto shaft like I had to get for my old Yanmar that does not have a live PTO. It always freewheels down regardless of what position the gear is in, PTO engaged or not, clutched or not. They also work well for those tractors that lock or substantially limit the turning of the PTO shaft when the tractor is not running or PTO is disengaged. You can still turn the PTO shaft to align the splines rather than trying to turn the equipment. It only makes the shaft about 6" longer. Havent had any problems with my Yanmar with the one way clutch attachment installed, just have to give it a shot of grease occassionaly for the ratchet mechanism.

 

[LittleBlueTractor]

Guys for about $20 you can "upgrade" to freewheeling on the PTO regardless of what stupid thing you do accidently or on purpose. Just get the little freewheeling pto shaft like I had to get for my old Yanmar that does not have a live PTO. It always freewheels down regardless of what position the gear is in, PTO engaged or not, clutched or not. They also work well for those tractors that lock or substantially limit the turning of the PTO shaft when the tractor is not running or PTO is disengaged. You can still turn the PTO shaft to align the splines rather than trying to turn the equipment. It only makes the shaft about 6" longer. Havent had any problems with my Yanmar with the one way clutch attachment installed, just have to give it a shot of grease occassionaly for the ratchet mechanism.

Thanks Gary, I think I found what you were referring to:

over-run coupling

Now I just need to find one for $20.!:laughing:

 

[kpbeddin]

Thanks Gary, I think I found what you were referring to:

over-run coupling

Now I just need to find one for $20.!:laughing:

Thanks Gary and LittleBlue, I didn't know such a thing existed; I suspect the $20.00 was last year's price.

 

[rocknrod]

OVER RIDING CLUTCH - Agri Supply

 

[kpbeddin]

I can't think of a reason to not own one of these; especially when using a rotary mower. It seems that even lowering the RPMs too quickly would cause the residual inertia to create unwanted stress in the driveline. Time to go shopping.