435 Build

[marrt]

You guys may recall my thread, a few months ago, about the death of my Subaru. The root cause was gas in the oil. Seems to be happening a lot lately. I didn't bother tracking down the exact source of the leak. I suspect it was the carburetor but I don't know for sure. By the way, I still have the old engine if somebody needs a part.

After a lot of hemming and hawing, I finally ordered the 35 hp Subaru "Generac" engine. I decided to go with this approach because I like to "mod" stuff especially Power-Tracs. I ordered larger will motors too. Probably don't need them with the larger engine but it should make the VD pump's life a little easier.

I'm ready to put everything back together but still have some concerns about cooling. And, given KentT's experience with the plastic fuel tank during a fire, I'm thinking about fabricating a steel tank. Also, this would be a good opportunity to relocate the hydraulic filter out of the tub and up near the tank. This could probably be accomplished by fabricating a smaller fuel tank so I have room.

I'll try to take a few pictures along the way.

 

[KentT]

Sounds like a fun project! What size wheel motors are you putting on it?

 

[joshlee]

Since I'm sort of new with understanding hydraulics, I'm just curious about the bigger wheel motors on the Pt 425. So I take it, the bigger wheel motors don't cause engine power loss, or work the tram pump too hard?

 

[Gravy]

You guys may recall my thread, a few months ago, about the death of my Subaru. The root cause was gas in the oil. Seems to be happening a lot lately. I didn't bother tracking down the exact source of the leak. I suspect it was the carburetor but I don't know for sure. By the way, I still have the old engine if somebody needs a part.

After a lot of hemming and hawing, I finally ordered the 35 hp Subaru "Generac" engine. I decided to go with this approach because I like to "mod" stuff?specially Power-Tracs. I ordered larger will motors too. Probably don稚 need them with the larger engine but it should make the VD pump痴 life a little easier.

I知 ready to put everything back together but still have some concerns about cooling. And, given KentT痴 experience with the plastic fuel tank during a fire, I'm thinking about fabricating a steel tank. Also, this would be a good opportunity to relocate the hydraulic filter out of the tub and up near the tank. This could probably be accomplished by fabricating a smaller fuel tank so I have room.

I'll try to take a few pictures along the way.

My 435 conversion is still working so well that I sorta forgot that I promised details. Have fun!

 

[marrt]

Kent, I'll have to look. I remember you made recommendations. I recall taking those recommendations into account. More tomorrow.

 

[marrt]

Joshless,

It's just like gearing in a normal vehicle. Larger wheel motors are like a lower gear. The pump has to run "longer" to fill the displacement on each revolution..which results in more torque. The tractor will run slower...but will likely spin the wheels before it runs out of mojo and stalls the pump/engine.

Tom

 

[MossRoad]

Since I'm sort of new with understanding hydraulics, I'm just curious about the bigger wheel motors on the Pt 425. So I take it, the bigger wheel motors don't cause engine power loss, or work the tram pump too hard?

As I understand it, the engine will still turn at 3600 RPM (max throttle) and the tram pump will still turn at the same RPM at full throttle and the tram pump will still put out the same gallons per minute at full throttle. The only thing different is the displacement inside the wheel motor is larger, so it takes more fluid to turn it 1 RPM than a smaller displacement pump would. So the larger displacement wheel motors won't spin as fast as the originals, but they will apply more torque.

My guess is the larger displacement means bigger vanes, gears, or pistons inside the motor. Bigger vanes, gears, or pistons would be the equivalent to lengthening a lever. Longer levers apply more leverage but take longer to go full stroke. That's why higher displacement makes more torque, but turns slower.

Of course, I don't know how that works at all, I'm just guessing. Someone will correct me if I'm wrong, and I'll get a free education.

 

[KentT]

You're understanding is correct. And with the tram (hydrostatic drive) pump, using a larger engine does not increase the maximum volume of the output, since both engines spin at 3600 RPM, but it increases the amount of pressure that can be produced by the pump (at any tram pedal setting), also increasing torque...

 

[MossRoad]

Gotcha. Thanks. :thumbsup:

 

[joshlee]

I understand now, thanks everyone.

 

[marrt]

Still working on this guys. BUT, I broke my lathe (stupid "learning experience"...waiting on parts) and it's slowed me down. Will report back once I get going again.

 

[cqaigy2]

Still working on this guys. BUT, I broke my lathe (stupid "learning experience"...waiting on parts) and it's slowed me down. Will report back once I get going again.

Sorry about the lathe. We all have our learning experiences so don't let that get you done, only stupid if you do it again, as i well know.

 

[marrt]

To finally get back to this thread, here's an update. Everything is installed and working. Only took 3 years. LOL. Actually, it's been finished for about a year, thanks to the help of a good friend. But I wanted to get some experience with the tractor before I posted an update.

If I were doing this today, I'd probably opt for a Kohler motor. I've heard a rumor Power-Trac offers a kit to make the swap (Subaru to Kohler) much easier. But that wasn't available when I started this project.

For the project, I needed to:

+ modify the pump mount weldment to match the new engine's bolt pattern.
+ create new engine "stands" (DOM tubing) so the engine sits at the same height as the original
+ cut out the rear of the tub to accommodate the new engine's slightly larger footprint and enable easy cleaning of the intake screen
+ increase the size of the wheel motor mounts to hold the slightly longer new wheel motors

For the wheel motors, I increased the capacity from 14.2 cu. in. to 22.8 cu. in. The the tractor was very fast with the previous wheel motors. I would estimate top speed was approaching 10 mph (same as my zero turn mower). The current speed is about 6 mph. This is fast enough for my use as I'm happy to trade speed for additional motor torque. The difference is literally night and day. I have no trouble climbing any hill and can spin the wheels, when pushing into a dirt pile, without a problem. I could go on about the differences due to the extra horsepower and wheel motor torque, but let me just say it completely transformed the tractor. The downside is additional strain on the tractor frame that may cause future problems. Also, the additional engine power can generate a lot more hydraulic heat...beyond the cooling capacity of the current configuration. I'm going to install a temp gauge so I can monitor the hydraulic oil temperature, which should never get above 80 degrees C.

Here's a few pictures plus some additional tweaks I made while working on the tractor.

Tub cut out.

A weldment was then fabricated to ensure the tub couldn't flex and to enable easy access for cleaning and filter changes.

Here's the final assembly.

The new wheel motor I used (1/2" longer than original).

Modified motor mount.

Final assembly.

As mentioned numerous times here, the Power-Trac parking brake solution doesn't work very well. So we mounted a lever on the left side that uses a cable and pulley arrangement. This works much better.

I also felt it was necessary to do something about the muffler heat. We fabricated a rockwool insulated assembly to surround the muffler. We then mounted a fan on the opposite side to blow air across the muffler for additional cooling. I can now rest my hand on the battery tray without getting burned.

I bought a new Bondioli and Pavesi pump. It's the same 21 cc pump as originally installed. Here's the model number.

And finally, some additional tweaks in no particular order...

Relocated exhaust exit.

Rear hood stops...allows internal swing arm to be removed, freeing up space for the spark plug wires (no rubbing).

New lights. These lights are fantastic. I like the "look" of the old lights better myself...but these work so much better with less battery drain.

 

[joshlee]

Awesome :thumbsup:

 

[m5040]

Great job! Should someone put these part numbers (pump and wheel motors) in the interchange post should someone need to replace their stock motors and want to increase the torque. I know I would go that route.

 

[MossRoad]

:drool:

 

[Marks481]

wow, that is some awesome fabrication. You are an inspiration. Thanks for the follow-up post.

 

[joshlee]

You will probably have more than enough power with that beast of an engine.

 

[cqaigy2]

Man oh Man! That's amazing!! and i second MR, :drool:

 

[woodlandfarms]

What I am looking forward to seeing is how the body survives. With all the added torque your wear is going to be increased.