MMM Cutting Height Adjustment

oldballs · Mar 20, 2017

My Kubota B2620 MMM cutting height adjustment knob will not hold the setting. The past few years it looses height now and then. I figured it was just a sudden bump that threw it off, and just reset it.

But at the start of this season it will not stay up at all. I can set the height all the way up to #4, but as soon as i let the hydraulics down it spins the whole knob around and drops to #1 which would scalp the grass. It will not stay on any setting except the transport position.

I took the apparatus apart this afternoon and can't see any obvious defect. Having reassembled it, I found that it worked okay for a few minutes, but then went back to the original problem. Maybe the cam teeth are worn out is all I can guess. Neither the Kubota Parts manual or the owners manual are of any help. Any help would be appreciated.

JWR · Mar 21, 2017

Quite strange. Never heard of this issue before. Normally the BX's have the full weight of the deck hanging on that cam and you cannot adjust the "drops down to point" to allow deck height adjustment unless you have the deck fully raised so it is resting on the hydraulics, not the cam. So most people I know have had the reverse of your problem -- they can't turn the knob (with weight on it) and typically break the knob trying. I see the cam is bolted on with a single nut in the middle of it. Might that nut be loose, allowing the cam to rotate too easily ? That does not seem likely since your knob is spinning when you lower the hydraulics. A puzzle for sure.

EricK · Mar 21, 2017

I had a very similar issue with my BX-24.

The issue is the plate where the adjuster knob goes through becomes worn and the shaft has play in it even with the bolt (on the underside) is completely tight. When the deck bounces, it causes the shaft to move and will cause the stop to jump out of the cam.

The fix is to add a washer (or something to pad out the plate). I added mine on the topside so it did not affect the mowing height and still allowed me to lock the deck in the top position. After the addition of the washer, it is possible to tighten the bolt too much and you will not be able to turn the adjustment knob and the adjuster shaft should be ridged.

This link can provide additional information.
http://www.zbcreations.com/b2620/B20 Series Loss of Deck Setting.pdf

JWR · Mar 21, 2017

Great info Erick ! If I may ask, who is zbcreations ?

EricK · Mar 21, 2017

Sorry, I have no idea. The document came up after many hours Google searches, not an easy find.

I installed it last mowing season any the issue went away. Also, added some blue loctite to the nut inside the cam to make sure it would not loosen. The document suggest replacing the factory nut with a nyloc nut but finding the correct size to fit inside the cam proved very difficult.

oldballs · Mar 21, 2017

Eric K..............you saved my day. Thanks for the reference. By putting a good size washer on top of the cam, the problem was solved. But I did buy a new cam ($45). Next time I'm under there I'll add that blue Lcctite. The dial is a little tight right now, but I'll follow that as the season moves along. Thanks again.

Cheers,
Mike

EricK · Mar 21, 2017

Mike,

Glad it worked out for you. I was pulling my hair out until I found that fix. I also bought a new cam and even the linkage arm in case the $0.20 washer didn't work. ;-)

Eric

RaydaKub · Mar 23, 2017

I've got basically the same issue on my BX. The finger on my arm is warn even worse than yours appears to be. It seems to slide down easily. I know the nut on mine is tight, I can tighten ittoo much so I can't even turn it. I've thought I might see if a friend can weld on a tiny piece of angle iron on the end of the finger just to square it up. But it requires so much tear down to be able to get a welder in there, I just dread the job.

oldballs · Mar 24, 2017

RaydaKub.............try that link that EricK posted in #3. There is a picture of the fix with a washer sitting on top of the cam. The part that you call the "finger" was worn as well on mine. But the washer fix seemed to cure the problem. For sure if you took that all apart to weld, that would be a big job in my mind. Yet, I haven't put my MMM to work that much since the "fix". We'll be soon to find out however.

Cheers,
Mike

JWR · Mar 24, 2017

In some ways I think this problem is blown out of proportion. Of course, if you have the problem, it is not minor and needs fixed. It seems worth investigating "how and why" this (in extreme cases undirected lowering of the deck) happened, especially because I do not think most of us BX owners have the problem and all of us want to avoid it. My data point is that I've put 500 hours on a BX2200 over the last 14 years and had no such problem. I am not a heavy or commercial user. Something specific must have been done or happened with those machines having the problem & it would be good for everyone to find the underlying cause.