Kubota Z421 - Hard to get blades spinning.

[oldntired55]

It should be either a Z421-KWT-3 OR Z421-KWTNC with a Kawasaki FS730V-AS17 engine 24hp.
The deck would be a RCK60P-400Z.


Just because there is only a few hours on a bearing doesn't mean they can't have problems. I one mower here that was constantly snapping belt. I had the customer pay a close attention as when it was happening. With that info I finally found one bearing that had what appeared to be minor catch during testing. It was enough to snap the belts on start up it happen to have been resting in that spot. Can even be rust in the bearings.

And some bearings have poor lube installed in them from the bearing factory which causes early failures. This deck uses 6205-RST bearings [6205-ZZ]. There should be grease zerks on the spindles but I see none in the images of the spindle housings so it is highly you ever greased the bearings.

From your further descriptions of the problem it is leaning to a poor clutch engagement problem and might be that the FT-LB torque of the clutch is too low for the deck load. Can even be that the grease in the bearings is hardening.

Or you can have grass and other crap like baling twine or plastic bags wedged between the blades and the spindle housings or between the spindle shafts and the bearings in the lower spindle housings.

So it can be a multitude of problems combined.

just a quick note here, i have seen several craftsman and jd mower decks fitted with grease fittings at top of spindles. yet on disassembly, found sealed spindle bearings, both sides not 1. my thought always was... how can the grease get into the bearings?? i dont think it was intended to force its way past the innermost seals///??// i had an old craftsman 42 inch , i put new bearings in and popped out the inside seals... i ran that deck for 12 yrs, on the same set of bearings... just sayin

 

[StarTech]

just a quick note here, i have seen several craftsman and jd mower decks fitted with grease fittings at top of spindles. yet on disassembly, found sealed spindle bearings, both sides not 1. my thought always was... how can the grease get into the bearings?? i dont think it was intended to force its way past the innermost seals///??// i had an old craftsman 42 inch , i put new bearings in and popped out the inside seals... i ran that deck for 12 yrs, on the same set of bearings... just sayin

Yes the OEMs are putting many cases -2RS sealed bearing which will not accept grease via the zerks. Now the -ZZ and RST can have grease force into them as they have trash seals which are not fully sealed. Even those need the inner seal removed.If you try forcing grease into the -2RS the inner seals tends to collapse into the bearing race jamming the bearing assembly.

 

[pwardxe126]

Bought a used Kubota Z421 60" with 207 hours on it. Great mower, super comfortable. My only complaint is that I have to be 1/2 throttle and up to get the blades to start spinning. Friend of mine has a lawn care business, he came and took a look at it and said that he could not find anything wrong with it. All the spindles are good. It is the smaller motor though, maybe 23.5hp. Anyone else have this issue with their Kubota?

I've had the same problem before. It was the PTO clutch. When engaged, it is supposed to slip momentarily. If it doesn't, it's such a hard jolt engaging all at once and stalls the engine.

 

[Auto Doc's]

Deck spindles come with lifetime grease already packed in the bearings... Don't they?

Most that I open up only have a minimal single shot of grease that resembles thinned Vaseline.

Grease fittings on most modern deck spindles that I see are just an illusion that you are buying a serviceable part. I open them up and find that most bearings have plastic inner seals.

For ones without grease fittings, I drill and tap them for a fitting that I can position for ease of access in the side near the base.

I disassemble new replacement spindles and remove the inner most seals, then pack them by well hand before reassembly. After that, they only need a couple of shots of grease once a season to maintain them and improve their life.

 

[RevB]

Full throttle......

They do make electronic soft start units that will ramp up the engagement voltage over a second or two. Also senses engine RPM to adjust the ramp rate. Ogura makes them and there's a company in NY state that makes them as well.

Why Does Your Zero-Turn Need a SoftStart Clutch Controller? | GDI

Having smooth clutch engagement every time you turn on your PTO is nice.Less of a teeth-rattling jolt when you engage your blades would certainly make any operator happy, but that isn’t why your commercial mower needs a SoftStart controller. Learn

www.gdimeters.com

https://ogura-clutch.com/files/pdfIMP/softstart2.pdf

Got one in a Bad Boy....noticably smoother engagement.

 

[Auto Doc's]

Smoother engagement also means increases clutch plate wear which leads to more frequent air gap adjustments.

 

[slomo]

Deck spindles come with lifetime grease already packed in the bearings... Don't they?

So the manufacturer says LOL. Just like Briggs and their no oil changes.

Lifetime grease, that was a good one.