My JD ZTrak 757 Repowering Experience

BryanStein

LawnSite Member
Location
Birmingham, AL
Just and FYI to hopefully help someone else going through something similar.

Bought a used JD 757 3 years ago. Back then it had a rebuilt engine and new hydraulics. I use for residential only. Put 30 hours on it in 3 years. Its a beast on my yard. Went from 2.5 hours of mowing to 50 minutes. Well worth it and will never go back.

Replaced the hydro pump this year. Metal in my pump ruined the valve plate. The guy I bought it from did not disassemble the Parker wheel drives to get the metal out. He simply flushed them. You can't get all the metal out without cleaning them out the hard way. It took 30 hours to get to the pump. It apparently had a broken shaft at one point. It won't happen again cause I can drink out of my hydraulic system now.

On the engine side, I dropped the valve (Kawasaki 25 hp). Horizontal shaft mowers are not a good idea. Cooling air comes from right behind the deck. In addition, JD decided to limit the air passages into that chamber just in front of the fan. I think they did this to force air across the hydro pump. Well, those two added together is a bad idea. Builds lots of heat on the engine with little dirty air to cool with.

Long story short, i was running on 1.5 cylinders after replacing a head. I never found the valve stem seal. I think it go lodged in my compression release and I can't get full power on one cylinder.

I decided to repower. Looked at Kohler (bushing on flywheel shaft) vs Honda (bearing on flywheel shaft). Both have nylon cam gears.

Searched the Kohler model. Found a hand full of mechanical issues. Searched the Honda model. All people complained about on the Honda was they couldn't bypass the electronic rev limiter. No repairs to speak of. One poster said the previous version of that engine runs at least 5500 rpm. Honda has better cooling and individual pipes for the push rods allows air direct access the cylinder walls.

I chose the Honda GX690, even though Honda said it was only 22.8 HP, but they use a different ASME standard. I never did figure out what the honda HP was per the ASME standard everybody else uses. I think its around 24 hp. The old Kawasaki 25 HP is actually 23 hp per the new standard. After my first cut, I'm not worried about power. Its got more than the OEM 25 HP Kawasaki.

Points for Honda

1) Moves 2x more air across the engine than the Kawasaki. You can feel the heat coming off the engine. I was amazed.
2) More power than he Kawasaki
3) Bearing on flywheel shaft, not a bushing.

The kit came with an adapter plate, a collar to fit between the pto clutch a engine, a new hydraulic pulley shaft to bolt to the flywheel, a new throttle cable and lever and a new choke cable and nob. I didn't need the choke cable. The throttle cable was needed because the old throttle cable was not long enough.

Engine Mounting:

Instructions were adequate at best. It didn't tell you which side of the adapter plate to put down. One side of the adapter plate was threaded, the other side was slotted for carriage bolts. I put the side down that used the carriage bolts. The carriage bolts were too long (rubbing the hydro lines) so I had to cut them off. Didn't have long enough bolts to bolt through the engine and onto the adapter plate. I used my original bolts but had to cut them shorter to get them to cinch up tight.

The adapter plate was labeled which side pointed towards the hydros, but alas I had to flip mine because my hydro pulley and pto clutch pulley would not line up any other way. Also had to use my old PTO clutch collar because the new one was about an inch shorter and put the mule belt (PTO belt) at an angle.

After all this I read the instructions the 8th time and realized it said insert the carriage bolts in the slot from the engine to the adapter plate (threads pointing up). So, I did it backwards. It just makes no sense to have to thread the bolts upward, through the frame, into the mounting plate. It made must more sense to put the slots in the adapter plate down.

Frame Modifications: (hopefully I am smart enough to upload photos)

The Honda engine is much wider (90 degree) than the Kawasaki. The seat plate had to be cut out to make room, and the vertical plates beside the engine had to be cut. I didn't removed the vertical plates until after the engine was mounted, then held them in place and marked where to cut. Turned out well.

I cut much more of the seat plate out than needed because I wanted to suck air from the top behind the seat and not from the front behind the deck. I thought maybe my hydros would run hotter. After an hour of use, I shot the hydro pump at 196 degree with an infrared thermometer. It didn't seem that hot. I plan to install a small hydro oil cooler this winter.

The muffler is top mount. Thus, the rear cover rests on the muffler when reinstalled. They tell you to cut the top of the cover out, but I'm planning on raising the cover about 3 inches to clear, and cutting slots in top of the back to evacuate the heat that tornado brings with it as it blows through the engine.

I'm very impressed with the honda engine. It really needs a side mounted muffler so the rear cover can be reinstalled without modification. It moves 2x more air than the kawasaki and I have not doubt it will run cooler.

Its interesting, the Kawasaki is a ground to kill, open to run engine. So the kill code is sending a ground to the coils. The Honda is a ground to run, open to kill. Thus, there is a relay on the Honda that opens the coil when the ground kill is sent. There is also another relay on the Honda that powers the harness and fuel solenoid. I don't know why the kit supplier chose to use a relay to power the harness.

When I first started the new honda, the check engine (oil pressure) light would not go off. After the kit supplier sent me a new oil pressure switch, I removed the old oil pressure switch. No oil drained out when I removed it. Turns out they had installed the oil pressure switch in the wrong port. So, I had to switch that port. No apology from them about that.

I developed a bad diode that shorted the parking brake switch. Essentially, the mower thought the parking brake was always on. So whenever I engaged my hydro levels, the kill command was sent. Took almost a week to find that. The kit supplier was patient with me as I worked through that. It wasn't until after I completely disconnected the new Honda engine, and the kill command was still being sent, that I believed the issue was not in the kit, but in the mower wiring. I would have thought the supplier would have offered that trouble shooting suggestion, but that was my idea in an effort to convince them that the problem was in their wiring.

Essentially, the kit is average. Just a few tweaks that would cost about $25 more and a little effort on the instructions and the kit would be superior. I am extremely impressed with the Honda engine, which is why I selected the kit. The kit needs better instructions. It arrived with a busted valve cover. The supplier replaced it and the oil pressure switch with no hassle. They do answer the phone and email. They even call back if you leave a message. They also sent me a wiring diagram for the JD 757 to try and help, so I guess I can't complain too much. They told me about having to cut the rear cover and the seat plate, but they didn't mention the two vertical plates I had to cut. Not bid deal really.

The three things that I wasn't pleased with the kit are:

1) The biggest thing I thought was bush league was the new throttle cable and controls they sent. You could not remove the nob off the control lever to slide it through the slot in the instrument panel. I called and asked them. When they said I'd have to cut it off to get it into the slot, or use my existing lever with the new cable, I told them that was a bush league, cheap thing to do.

2) Another thing that ticked me off is they didn't once apologize for having the oil pressure switch in the wrong port.

3) The last thing that bothered me was when I told them the instructions could be better and a simple diagram showing how the plate is mounted would greatly help, they replied that this is there best kit. They sell one or two a day. Well whoop te doo. I'm no ace mechanic, but I've done almost everything but rebuild transmissions. I found the instructions lacking, and they could have at least acted like my thoughts counted for something.

I still have one potential outstanding issue. The throttle barely holds at high RPM. It has a spring that keeps pulling it back down. I got better as the mower warmed up. I hope it works itself out. If not, I'll have to call them to address that issue.

All in all, I'm pleased. Half way through I was regretting not using a Kohler or another Kawasaki, but after seeing the Honda run, I'm pleased.

Hope this helps someone else.
 

Attachments

  • Rear.pdf
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  • Rear Cover.pdf
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  • Removed metal.pdf
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  • Rt Plt Cut.pdf
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  • LFt Plt Cut.pdf
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  • Seat Plt Cut.pdf
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  • Rt Rear Engine.pdf
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  • Muffle Rear Cover.pdf
    208.8 KB · Views: 374

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