Mule engine swap

[jwmorris]

Had a half shaft break on one of the mules down at the farm and a buddy of mine said another friend of ours had one with a blown engine sitting in a field. I wound up just getting a new half shaft but he picked up the mule for spare parts before they scrapped it.

I looked it over and decided it could be brought back to life. Started by hosing it off, removing the drive and making a simple fixture so I could locate the new engine in the right spot for the drive to still work.

 

[jaydee325]

My local Kawasaki dealer sells quite a few Mule replacement engines on eBay. These are a factory direct bolt in replacement. Might be an option for you.

 

[jwmorris]

The Diesel engines for these don’t seem to have a very good reputation haven’t seen any listed. The gas engines run around $2700.

 

[grsthegreat]

So sad they let it get in that shape.

 

[yanmars]

I got one at a low price as the owner was told it had a bad engine. Got it cheap enough that it still would have been a good buy with a replacement engine. As it turned out it was just an intake manifold gasket leak. Simple and cheap fix.

 

[jwmorris]

The taper the drive clutch bolts to is located on the OD by the flywheel.

So I found some suitable material to make an adapter.

Machined the two parts for a press fit.

Just under 7 tons To get them together.

Finish machined, drilled/tapped and broached to go from a 1 1/8” 5/16 key shaft and mount the converter.
I also added drilled and tapped 1/4-20 holes every 120 deg front and rear for set screws and SHCS to ensure the outer ring can’t move on the inner hub.

 

[jwmorris]

Don’t need the starter hole but the factory steel engine plate is a good starting point to work off of.

I had thought about going dirt cheap and using a Predator engine or maybe a B&S but since the mid ‘80s, I have been a fan of Honda engines and picked up a GS690 for just under $1500. It’s not exactly a “drop in” but will fit.

 

[jwmorris]

Lots of in and out, log story short, the height is 1.375” higher than the original mounting point is the right elevation for the engine, will still be under the bed. The cross tube had to be notched, removed sections, inverted and welded back in.

Also, made my oil filter relocation/oil cooler block. Used the factory Honda seals at the block and -6 AN/Teflon for the rest.

 

[plastikosmd]

Nice fabrication

 

[jwmorris]

I got a little sloppy on the spacer plates, the outside, spots anyone could actually see look OK but the inside looks pretty bad. New plasma consumables ordered, it allows the engine to be removed without having to pull the crank hub. Went overboard on fasteners but I promise it will stay put.

The engine is spaced off the factory engine plate with 3 aluminum plates a 1/4” thick each.

Used -6 high flow AN fittings and Stainless steel/Teflon line to go from the engine, oil filter, oil cooler and back.

Blocks crooked but I transferred from the factory part, guess the outside of it isn’t square. No worry, this side is right up against the transmission.

 

[ruffdog]

Keep us posted!

 

[jwmorris]

Attached The tank to a gear reduced motor, filled with soap, water and a 1000 bb’s. Rinsed and refilled a few times.

Adapter plate(s) as well as hub finished, then drilled and cut 1/4” plate for exhaust flanges.

Back in one more time, then started to work on the cable bracket so it clears the engine cover.

 

[Zebrafive]

What HP is the Honda? Super job fabbing and installing!

 

[jwmorris]

It is 22hp net, 27 or 28 gross.

The 3 cylinder diesel only had one 1-1/4” exhaust pipe, wonder if that’s why they had head/over heating problems?

I used two stainless “J” bends, as well as most of the original pipe to mate the new engine to the muffler.

You can also see the alteration in the shift cable bracket, the bend was cut off and flipped over to reinforce the other side.

 

[ruffdog]

Will the different torque and RPM curve be a problem for the clutch?

 

[jwmorris]

That was my first thought, I found this.

The diesel Mule was powered by a water-cooled, three-cylinder, four-stroke Daihatsu DM950D diesel engine rated 24.5 horsepower at 3,600 rpm. It gave the Mule a hauling capacity of 800 lbs. and a 1,200 lb. towing capacity. Top speed of the Mule was limited by a governor to 25 mph.

Another site listed “Torque RPM” at 2800 rpm, not sure if they were trying to say “peak torque” or not though.

Peak HP on both are at the governed 3600 rpm, peak torque on the Honda is at 2500 rpm though. So they are not the same. Not sure if the 300 RPM difference will be a deal breaker.

 

[jwmorris]

I blocked off the air box intake from the fan and epoxied a tube into the top of the air box, so I could connect it to the factory air intake up on the back of the roll bar vs sucking air from under the bed. Using both the original mule air cleaner element and the Honda element.

The diesel mules have two radiators, one up front and another under the seat. I built a 12 volt air compressor for our gas mule and wanted to do the same with this one but decided to use the space (and existing mounts) to mount an oil cooler and full size oil filter. This doubles the oil capacity and I can get better filters for less than the little Honda ones and a much easier location to change. Lift the seat and it’s all right there. The oil cooler/fan also had a thermostat, I connected it using a relay no longer needed for the old diesel engine.

Here you can see the air intake tube, added exhaust, pipe, flange, heat shield and the flipped/reversed section that makes up the cable bracket.

Its been too many years since I drove this one with the 3 cylinder diesel. It was when it was new and my take away at the time was that the diesel was quite loud compared to the gas one we already had. The Honda is noticeably quieter and more powerful than the Kawasaki gas twin mule we have but that one has more than 5300 hrs on it, so not a very fair comparison.