[Homecutter]

Greeting all,

I have a 1999 Yazoo-Kees ZT-Max (ZKH52253) which started to chatter on the right side and quickly lost power. I ordered a rebuild kit hoping that would do it but when I disassembled the pump I found the following:

1) Two of the pistons were stuck fully depressed into their bores. I freed them and cleaned up the bores and now they move freely again.

2) The face of the piston block & end cap valve seat had grooves worn into them (see pic).

A new piston assembly is $55 and the end cap valve seat is likely $150. I can get a new motor for $400. Not sure which way to go.

Another option I'm considering is having block & end cap reground. I'd estimate having to remove 0.010 max per side. Do you guys think this will work?

Lastly, my neighbor has a John Deere 757 and his hydro pumps operate like a Swiss watch dipped in butter compared to my herky-jerky old ass Yazoo :laugh:. I've often thought about getting better/newer hydros for my Yazoo but I'm not sure how to go about it. Now that I may be ordering new pump all I can think to do is get that same model number vs trying to figure out a suitable sub that's a newer/better design. Any thoughts on this?

Thanks Gentlemen!

 

[piston slapper]

Replace the pump..
The head is shot ..grooves between the kidney ports ..and the rotor pistons will stick again...
The other problem is that the pump ingested some metal from somewhere else ..a bearing ?..and you'll need to find the damaged part so that the same failure doesn't happen again..

 

[Restrorob]

What Slapper said ^^^^^^

the end cap valve seat is likely $150.

That end cap alone will set you back a little over 300 bux !

 

[Homecutter]

Thanks Slapper - I appreciate the feedback. I'll order a new pump. Any thoughts on where the other damaged part is likely to be or any ideas on troubleshooting the system? This is my first hydro rodeo.

Thanks Restrorob - "That end cap alone will set you back a little over 300 bux!" Yea man, I ended up locating the part number 2513016 END CAP KIT (STD) and you're right $300!! That's outrageous!

I have a milling machine and may try to re-face the block and end cap. Got nothing to lose at this point. I'm a little worried they might be hardened to much for HSS tooling but we'll see.

I noticed the newer Hydro Gear pumps have a replaceable "valve seat" in the end cap vs using the end cap body, smart. This makes it a $30 repair vs $300 repair.

 

[ricky86]

Well Homecutter, the area that is damaged is the ports for the wheel motor inlet and outlet. If the other components in the pump are intact, brgs etc, (which you do not state). there is a distinct possibility that the debris came from the wheel motor. Does that make sense to you? If not, just replace the pump. FYI, cleaning the cylinder block, after fine debris has made them stick, isn't a good idea. It is amazing just how little debris will get into the wheelmotor after a pump failure. Not true the other way. Feeling lucky?

 

[Homecutter]

So I went ahead and resurfaced both parts on my HF mini-mill. I took 0.005 off each one then polished them both with 3 grades finishing off with 320. no more grooves!! The block face is smoother because is has less cross-sectional area to polish and I spent more time on it vs the end cap. I'm pleased with how they turned out which is better than I expected. I'm degreasing them overnight in a bucket. Will blow them out and re-clean them a few more times before I reassemble to be sure I get out all the metal shavings and aluminum oxide particles from the sand paper out of in inner nooks and grannies. Here are some pics of my progress

 

[Homecutter]

My repair was successful and the pump is working great. Machining 0.005 off each side is not an issue as the piston springs will take up the slack. If you have one of the older Hydro Gear (crappy designed) pumps without a replaceable valve seat in the end cap and the surfaces are found to be worn consider this an option vs buying a $400 to $500 replacement pump. Over the years the right side tracked slower but now it’s tracking at the same speed due to the block face & valve seat no longer leaking. As for what caused the 2 pistons to stick and right side shut down I did not investigate… maybe drive motor debris? I installed a rebuild kit which is just a gasket & O-rings, replaced the hydro filter and put 2 gallons of 20W-50 in the tank with a magnet on a stick to catch metal debris so we'll see how it goes. I only use the mower for my property so I can tolerate some downtime.

To conclude, the two stuck pistons were the reason the pump quit working, not the grooves worn into the block & valve seat. Simply freeing the stuck pistons would have got the pump going again. In hindsight perhaps tapping on the pump would have freed them up. Re-machining the faces was just a bonus and restored drive speed. Of course I knew none of this when I started the repair. Live and learn!

 

[Shaw77]

I know this is an old thread and you may not have the mower anymore but how long did this fix last? Just had the death chatter Saturday out of my left side after replacing the right side last year. Lost power and barely made it back in the barn. Didn't really want to shell out another grand for a pump and motor if I can mill it down myself and save some coin. Thanks for any info.