After looking into the cost to rebuild the motor on my Wheel Horse 417-8, I decided to start looking for a new motor to replace the old one. I settled on a Predator 420 single cylinder engine from Harbor Freight. Predator is Harbor Freight’s home brand name for small engines, but it’s simply another Honda clone made in China. The motors have a reputation for being reliable and cheap which fits both my requirements. This is the hemi version of this motor and is rated at 13 hp and about 20 ft*lb tq. Other bands rate this motor at 15 hp. So, mine may have a little more power than stated. The motor also comes with keyed electric start which I also wanted. One small issue is the PRO shaft on the new motor is 1″ diameter while the old motor’s is 1-1/8″
To locate the new motor, I have to make sure that the PTO shaft is in the same position as the old one. The pulley that powers the tractor as well as the front PTO clutch sit on the shaft. To find where the PTO shaft needs to go I first had to put the old motor back in and measure the PTO shaft’s location in all three dimensions. I ended up clamping a carpenter’s square onto the frame and, using another square, measured the location from the front corner of the frame.
Next, I removed the old motor again and put the new one in place. Here’s a pic of the new motor fresh from the box. It’s bigger than the old one but I plan to working to make it fit under the hood.
To locate the new motor. I moved it around until the PTO shaft was in the right location along the length of the tractor. I also measured the height to the PTO shaft and found that it was 1″ lower than needed. Finally, I put the drive pulley and clutch disk loosely onto the shaft and nudged the motor into position out from the middle of the tractor. The old motor sat on a 1/4″ thick plate that I planned to reuse meaning I need to make some 3/4″ spacers to raise the engine.
To address the difference in PTO shaft size, I decided to make as spacer out of some 1-1/4″ bar stock. First I drilled out the center and bored it to size.
Here’s a pic of me testing the fit of the spacer on the shaft and inside the PTO clutch disk.
Once I knew it fit, I used to the mill to cut the keyway slot. Only the drive pulley is keyed so I didn’t need to mill along the entire length of the spacer. Then it was back to the lathe to trim off the excess.
The spacer also required a 1/16″ taller key. I machined one out of some 3/8″ key stock and fit it to the PTO shaft. Below is a pic showing the test fit with the spacer on backwards before trimming down the key.
Making the spacers was simple enough on the lathe. I used some 1″ aluminum bar that I drilled out to a little over 3/8″ and parted off quickly.
I bolted the plate down with the new spacers and re-positioned the motor as before. I then used some paint on the end of a short bolt to mark spots to drill holes for the bolts that will hold the motor to the plate.
After that, I put the drive pulley and belt back on and was able to take a test drive by pull starting the motor. I drove around some and the motor performed as expected. It seems about the same as the old motor except for the exhaust note.
Here’s a view of the other side showing the drive belt. Obviously, a few panels were off for my test drive.
Well, now that it runs again I think we can call it done! Nah, of course I’m not done yet. Next, I’ll be merging the electrical system of the tractor and new motor together. I want to have all the dash controls on the tractor working again and the hood back on as well.