sudden and violent PTO engagement with new Kubota MX5800

[rbtjr]

Good thoughts. I try to have the mower level when I engage the PTO. This also raises the blades up so that they can't hit anything. I think that if anything the slip clutch was too tight. I am replacing the shaft to the mower, and the slip clutch is an integral part of the shaft, so I will have a new slip clutch and a better shaft (longer, so more overlap of the two halves of the shaft). I am not sure why the blades sometimes touch. This weekend I will take off the blades, make sure neither is bent, and re-torque them. I have already measured the up-and-down flex of the tips of the blades, and they are both the same. And the tips of both blades at rest are the same distance from the underside of the deck, measured at the same point on the underside of the deck. It may be the combination of the tractor PTO engagement and the HD mower with very heavy blades. I will know more after this weekend. I'm going to try PTO engagement at a little higher rpms than the 800 rpm lowest idle speed. I will probably calibrate the slip clutch. And I may experiment with how the blades are positioned when the PTO is engaged (positioning the blades by hand with the tractor turned off, of course, and not with me under the mower). I have the thought that if the blades are both turned 90 degrees away from their widest configuration when up to speed, that may reduce the inertia of the blades enough to make a difference. I am referring to the blades being turned 90 degrees away from the direction in which they rotate. We'll see.

 

[ovrszd]

I've engaged my various brush cutters thousands of times. I've never "positioned" the blades.

I'm pretty sure if I removed the 3 blades from my large cutter and the 2 blades from my smaller cutter I'd find at least one bent.

Not sure what the problem is, but pretty sure it's not the cutter.

 

[rbtjr]

Thanks for the feedback. I believe that if the PTO engagement on the MX were the clutch style, where you could feather the clutch and gently engage the PTO, I wouldn't be having these issues. The MX PTO is engaged suddenly, no doubt by a solenoid being electrically activated instantly which in turn instantly activates the hydraulic-fluid flow to the tractor PTO shaft.

I have had bent blades on a cutter before and had no problem until they were bent so much that they were able to get stuck one blade under another. I don't think that is the issue, because of the measurements I mentioned before.

Thanks again.

 

[boggen]

just tossing stuff out there. to toss it out there.

have you properly leveled the rotatory cutter? flat surface both tractor and cutter. and leveled the deck with the gauge wheels and 3pt hitch?

if you have a quick attach or pat's easy hitch, have you removed them from the 3pt and hooked directly to the cutter?

have you removed cutter from tractor, and gotten up under it. and physical checked out the bolts/nuts are tight and to rated torque specifications?

is the physical frame work on top of the deck tight and secure?

are the blades straight?

have you removed the blades and physically tested to see if one is heavier than the other blade. other words dealing with a finishing mower blades and balancing the blades after sharpening them.

is the stump jumper if you have one in working order?

do you have your check chains and sway bar/chain in place on 3pt hitch.

is PTO shaft properly greased. not just the ends, but also the shafts that slide in/out of each other.

have you correctly cut the PTO shaft to length. most times you buy a longer PTO shaft then need to cut both the shield and then also cut each piece of the shaft to correct length for your tractor. dealing with correct amount of overlap.

is the PTO shaft correctly sized. and rated for X amount of HP for tractor and cutter?

i do not know your hydraulic schematics. instead of lifting the cutter up into the air and engaging PTO. let the cutter rest on ground (flat open area no weeds to cut) and engage.

i do not know your hydraulic schematics. curl bucket / uncurl FEL bucket, while engaging PTO. some power goes to FEL in idea rest of power goes to PTO. (not a clue if it would work, talking out my rear)

have you installed an overrun clutch on the PTO and got one that is going in wrong direction?

is there a PTO short extension shaft, beyond general PTO shaft?

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upload a video to youtube and post it. what you think is really bad, maybe, *meh* ya what ever and continue on, to others.

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with above said, use it and abuse it. i would imagine hitting a stump / branch with rotary cutter and stump jumper / blades spinning out of way, most likely drives a shock through the system worst than just simply starting it up and getting things going. granted be nice for feather effect. but you also have other PTO implements, that may need an extra kick in the pants to start turning initially.

 

[rbtjr]

Thanks for the thoughts. Yes, mower is leveled. Yes, Pat's QH is installed. I used the mower twice without Pat's and had the same problem, although no shutdown. All mower top-side bolts are good. I'm going to remove the blades this weekend, check them thoroughly, put them back on if they're okay, and re-torque. I did measure the maximum flex of the tip of each blade, and the distance between the tip of each blade to the underside of the deck--with the blades in the same position under the mower for each measurement. All distances were very close. Stump jumper seems to be okay but I have not removed it and hope not to. Yes, sway bars are good (telescoping type). Yes, PTO shaft greased. The PTO shaft that came with the mower was a little too short with Pat's QC installed. I am putting on a new one. The overlap on the new shaft will be much better and the new shaft will not need to be cut (i.e., is not too long). Both original and new PTO shafts are properly rated. About lifting the mower or not, that's an interesting thought. I have been lifting the front end of the mower to level the mower and PTO shaft for engagement, which also insures that the blades are touching nothing. But that has to result in constant pressure on some part of the hydraulic system to hold up the weight of the front of the mower. I have no idea if the PTO-related hydraulics and the 3PH lift hydraulics are so inter-related that the 3PH hydraulics could affect the PTO engagement. Same comment about curling the FEL bucket while engaging the PTO in order to divert some of the hydraulic flow. BTW, Kubota says that there is nothing I can do to the tractor to soften or dampen the PTO engagement. No overrun clutch. Yes, I used a short tractor-side PTO shaft extension a few times because the original mower PTO shaft was not long enough to have as much overlap as would be ideal. The extension didn't seem to affect anything but it did make the PTO shaft sturdier due to more overlap. I stopped using the extension because of concerns about damaging the tractor-side PTO shaft. The new longer PTO shaft will fix the overlap issue.

Thanks again for the thoughts.

 

[deanocraft]

I second the idea of starting the pto with the cutter on the ground. Not in tall grass, but on a nice flat surface. The wheels being anchored to the ground by the cutter's weight will absorb a lot of the jolt you are feeling.

 

[CobyRupert]

Probably not the problem here, but......
Can the two pieces of the PTO shaft be put together wrong? That is, are the two universals 90 degrees out of phase with each other?
Seeing how the vibration stops once up to speed, and most pto shafts can't put together incorrectly, this is probably not the problem, but something to keep in mind on PTO vibration problems.

 

[DLTTrekkers]

The shape of the pto shaf.....triangle.....lemon.....or square ? Square can give you problems !

 

[Catchad81]

When I had my M7060, that was my very first issue with the dealer. I demo'd the tractor without a cutter I had and didn't like the engagement rated. They changed an orifice in the supply line, but it only helped a small amount. Purchase a new cutter with the tractor and it was the same way even choking off the tractor at idle when the cutter was new. I did learn you can feather the turn button just a bit. That being said, traded that tractor in on a deere and it engages alot better (slower) than the Kubota, same cutter or not.

 

[DieselBound]

I have very limited experience so far with my NX, but the handful of times I've cranked up my 6' BH 286 (old battle-hardened beast I bought used!) I've not felt any slamming. There's a bit of shaking, as is pretty standard until blades start to balance out. The electric PTO seems just fine here: I don't see any real difference between it and the manual "clutch" operation on my B7800 (other than there doesn't seem to be any meshing issues like I have now and then on the B7800).

How much overlap on the PTO shaft segments do you have? Minimum, from my understanding, is 6" (or is it 7"?). I think I figure the shaft on my BH 286 to be about 7" (was considering an extension). I think that this issue with the PTO shaft needs to be isolated.

What series PTO shaft?

What happens when nothing is attached to your tractor's PTO output shaft and you engage it?

Do you have any other PTO implement that you can attach to test with?

At this point it's hard to determine whether this issue is due to an issue with the tractor or with post-tractor. Given that you've actually managed to stall the engine upon start-up of the cutter I'm thinking that this is a post-tractor issue: something is so horribly out of balance that it's presenting a huge drag that stalls out the engine.

After testing w/o any shaft attached you might then look to hook up and engage with a slackened slip clutch (to test the shaft).