John Deere 400 - 26hp Diesel Swap

Hi Everybody,

Over the last year I've really got into working on and tinkering with mowers. I have a 317 and a 330 with a 16hp yanmar diesel. My old man has a 455 with a 22hp yanmar. We are both big fans of the yanmar 3-cylinder diesels.

I picked up an old dilapidated John Deere 400 a few months back for $350. I knew there was something wrong in/with the engine, but since it came with a hydraulic plow I decided to buy it. A mower dealer had it sitting on their back lot for a few weeks and wanted to get rid of it. My original plan was to tear into the motor to find out why the driveshaft would turn freely with no compression. I initially thought it could be stripped timing gears. After pulling off the heads and finding no movement of the pistons, it sounded like both rods were broken.

I decided that the project was worthy of attempting an engine swap on. I started looking for a 20+ hp horizontal shaft motor to stick in. Repowers on these 400s are common and typically not very involved. My love of yanmars took over when I saw a JD 3215a fairway mower come up on marketplace I decided it would be the donor. After some preliminary research, I determined that it would have a yanmar with 25-29hp. I drove 2 hours to pick it up and barely squeezed it on the trailer.

The engine fired up instantly every time I went to start it and sounded perfectly healthy. The machine only had 1200 hours on it, and the hour meter was still functioning. The guy I bought it from had purchased 3 fairway mowers off a golf course to resell. I picked this one up for $1200 and felt like the motor alone was easily worth that much.

I began pulling the yanmar out of the 3215a. It came out without too much trouble, however it was readily apparent how much of a pig it was after getting it out and onto the garage floor. Reading through the service manual, it appears my engine is 26hp. After pulling the yanmar, I went back to the 400 and stripped it down the basically the frame, transmission, and hydraulics.

Ultimately, this engine swap is going to require serious modifications to the front end. I had to machine an adapter to mount the factory PTO sheave to the new engine. I had to make motor mounts and mounting brackets from scratch and weld them to the frame. Tonight I cut out a piece of 5/8in plate on the bandsaw and will start machining an adapter for the drive shaft from the back of the motor to the transmission. I am also working on shortening the driveshaft.

I will also need to modify the steering column side panels, the hood likely will not fit anymore so I will have to make a new one. I will have to mount the radiator and oil cooler off the front end of the frame. Hydraulic inlet and return lines for the oil cooler will have to be lengthened. The battery will be mounted transverse to the steering column. I am going to use the 3215a wiring harness for all of the electricals. And I'm sure there are plenty of other things that I am not yet aware of.

I have made a good bit of progress on this project and have committed to seeing it through to completion. I have filmed the entire process and have 4 videos edited up so far. I am currently working on the 5th. Since I spent all of that time filming I did not take a lot of photos. I have added some of the photos below.

I will add links to my videos after my 7 day new member probation is up.

If your videos are on YouTube. Use the YouTube button to embed them!

Part 1 - The examination and diagnosis

Part 2 - Pulling the diesel

Part 3 - Adapting the front PTO pulley

Part 4 - Motor mounts and bracketry

Neat build, I’ll be following this closely. Going to do a restoration or just a repower?

Rustbucket Garage wrote:

Neat build, I’ll be following this closely. Going to do a restoration or just a repower?

I just want to repower it and hopefully have a good, reliable, overpowered mower with a 60in deck. lol

I got quite a bit done on the rear crank pulley-to-driveshaft adapter. From the last picture of my first post where I roughed out the shape on the bandsaw, to where it stands now.






All that's left to do now on it is to mill a keyway for a 1/4in woodruff key and then drill through 90 degrees from the key to add in a roll pin. After I get it finished I will mock up the engine and cut the drive shaft down to the correct length.

I haven't been online lately to update my thread. However, the diesel swapped 400 is basically finished now. Below are the rest of the videos in the series if anyone is interested in watching the progress.

It runs great and has tons of power. The most difficult part was probably taking the control module based wiring harness off the 3215a and modifying it to just run off of switch inputs.

I would be happy to elaborate on any aspects of this build if anyone is interested!

Nice work! Going to try and make some front body work or leave her as-is? I imagine it would be tricky with the radiator being as high as it is.

Yanmar sounds absolutely minty

Rustbucket Garage wrote:

Nice work! Going to try and make some front body work or leave her as-is? I imagine it would be tricky with the radiator being as high as it is.

Yanmar sounds absolutely minty

Thanks! I am definitely going to build a grill for the front and I'm also thinking about building an engine cage that ties into the rad support. I may see about making some sheet metal to cover the top and part of the sides, if possible.

What a neat machine. I will post a picture, I think it is from here, but I’m not sure. Sorry, I can’t give proper credit, maybe someone else can. But this ‘caged’ front end is a favorite of mine. 

Love what you're doing here! I've saved all the videos to my "watch later" and will catch up with them soon enough, I'll be laid off until spring very soon and will be able to set aside time and enjoy them! Lol

Nice fab work based on the photos! I'm looking forward to watching your machine take shape.