Converting a zero turn mower to diesel engine

   / Converting a zero turn mower to diesel engine #1  

Tenn_Blue

Silver Member
Joined
Nov 14, 2007
Messages
154
Location
N.E Tennessee
Tractor
Deere 2320, Bobcat 322 mini-ex, Bobcat 763 skidsteer
I have a Deere m669 zero turn mower with a blown engine. Originally came with a Kohler 23 hp twin engine and a 5' iron seven cutting deck.

Long story short, I would like to adapt a 3 cylinder liquid cooled mitsubishi diesel engine in it. I already have the engine laying around.. Making it fit necessitates changing the mower drive train. Since the diesel turns slower, I will have to speed up the mower drive train. Thinking abut using a belt-fed right angle gearbox to go from the horizontal crank to the verticle mower shaft (instead of the long belt and numerous pulleys of the original design). That also helps shorten the package since the new motor is longer than the original one. I can use the pulley ratio (crankshaft to gearbox) to get the deck blade speed back up where the gas motor's would be.

Also can change the pulley size on the hydraulic pump to get the speed back up there.

What issues do you see with this change? I have reasonable fabrication skills and can make the mounts, pulleys, etc that I don't have. I know the "easiest" thing would be to buy a replacement engine, but I want a diesel ztr, and already have most of the parts I would need to make the conversion.

One other question - with the original configuration, what percentage of the engine power is used by the mower deck, and how much goes to the hydraulic drive train? I know deck load depends on what you are cutting, but trying to get some idea where the power goes for sizing the mower drive train...
 
   / Converting a zero turn mower to diesel engine #2  
If you are turning the variable speed pump with the diesel, the HP necessary drive the VSP is variable as to the displacement of the pump. Sometimes you are creeping along using little HP, and at other times, you are flat out moving. There is a ratio of ground speed to cut quality also. If the deck is belt drive, you are transferring some of that HP to the deck spindles.

With you old 23 HP engine, you might have been using about 15 HP for the deck, and the rest for the variable speed pump. Some efficiency is lost from engine to pump, and then from pump to hyd wheel motors. Usually, I don't hear the engine change speed as I change speed. It may change speed if you cut uphill. You can definitely hear the engine struggle to cut heavy grass. Sometimes slowing down will allow the extra HP for the deck spindles.

What is the HP of the diesel you are thinking about? Diesels usually have more guts, and will not stall as easy as a gas engine.

You have the right idea about changing the pulleys to keep the original rpm, and therefore blade tip speed.

Since the pump volume is based on speed, and the setting of the squash plate position, using a diesel, will give less rpm for top diesel speed. You will need to compute the change in rpm necessary to bring the pump speed back up to the original rpm. My Dixie Chopper engine is turning a gear box that is turning two hyd VSP pumps. If your pumps are turned by belts, then you can use different pulleys to accomplish the task. The Dixie Chopper line includes some diesel engine powered ZTR, but I have never looked at them close.

Your diesel might weigh about 100 lbs more than your Kohler. Motor mount adaption, muffler position, larger battery, etc. .

You can probably change over from gas to diesel, with a lot of work, but would not a new 25 HP Kohler do quite well?
 
   / Converting a zero turn mower to diesel engine
  • Thread Starter
#3  
The original hydraulic drive pumps were driven by a pulley/belt off the flywheel side of the kohler. So I can run a different ratio pulley off the diesel engine to make up the difference in engine speed.

The mitusbishi diesel is one of their common industrial motors - output is between 17 and 23 hp depending on application. This one came out of a Toro greens mower and was speced at 22 hp. So the power should be a good fit... I still have the toro so can scavenge all the parts I need off it.

A replacement kohler would be around $1,500+ (best price I have found...) :( vs already owning the diesel engine. - If I had to BUY the diesel, I would definitely go gas replacement, but since it is just sitting around...... :) Aside from the time (I'm retired...), I think I have, or can make, most of the stuff needed to make the switch. So there should be a cost savings in going with the diesel.

Also, this will be cutting 3-6 acres of yard/field, so the diesel's lower fuel use should help. I use off-road diesel and keep a tank at the property.

I have other cutting equipment, so am not in any rush to get this done - it's more of a project to build a better tool for future use. Worst case, I go buy the Kohler, but if I can make this work, I think it would be a better mower as a diesel!
 
   / Converting a zero turn mower to diesel engine #4  
Are you talking vertical or horizontal engine. I have purchased 25 HP Kohler from Small Engine warehouse for around $700. You can get these engines with 1 in or 1 1/8 in shaft.

There is no reason that you can not try, except time needed to start cutting. I have two Magnums 18 HP on the 42 in Dixie Choppers, and 25 HP on the 60 in models. .
 
   / Converting a zero turn mower to diesel engine
  • Thread Starter
#5  
Horizontal shaft. Thats the problem! The bigger horizontal shaft engines are a lot more expensive compared to the vertical shaft ones.

I actually initially thought about trying to convert the mower to use a vertical shaft engine because of the price. The mower deck would be easy to convert. The original configuration takes a belt off the back of the horizontal engine shaft, then around pulleys and down to a vertical pulley shaft on the deck. It uses a really long belt! But the hydraulic pumps are on a horizontal plane. I would have to right angle the drive to the pumps somehow.

Given that most of the power goes to the deck (based on what you said before), I guess a vertical shaft engine configuration would be more efficient.
If the diesel idea falls through, I may revert back to this idea, but I REALLY want the diesel idea to work if possible.
 
   / Converting a zero turn mower to diesel engine #6  
I think that I would look at the Agri Supply brush hog gearbox, it's 119 bucks before shipping, and at a 1-1.47 speed increase would get your diesels output up around the 3600 rpm the the gas engine had as well as giving you the right angle drive that you need. GEARBOX 40 HP, SPLINED INPUT SHAFT - Agri Supply
 
   / Converting a zero turn mower to diesel engine #7  
I went through this with my JD 680 ZTR last year. I waited until after mowing season and started watching the specials at Small Engine Warehouse, Jacks, OPE, Brand New Engines,Small Engine Suppliers, etc and Ebay. Sure enough OPE started running no reserve Ebay auctions on some CH670 horizontal shaft engines in early October. They had quite a few so I kept watching the auctions and each one sold for less and less and I finally bought mine for a little over $600 including shipping. I should have waited, they got even cheaper. I like the idea of a diesel conversion but it sounds like time is on your side. Chances are if you do some patient Internet watching you can replace your Kohler engine for less than you think this fall/winter. The great things about the CH Kohlers are that They all use the same basic block,if your JD uses the flywheel as a PTO drive with the stub shaft, they all are drilled and tapped for the shaft attachment, they all use the same wiring, so that's easy to decipher when it's time to splice your JD electrical plug on to it, and some of the JD mowers don't even use the engine crank/pto, but sounds like your mower does- there are tons of Kohlers spec'ed close enough to what JD used to easily make the adaptation work.
 
   / Converting a zero turn mower to diesel engine #8  
You know, I went through this with my JD 680 ZTR last year. I waited until after mowing season and started watching the specials at Small Engine Warehouse, Jacks, OPE, Brand New Engines,Small Engine Suppliers, etc and Ebay. Sure enough OPE started running no reserve Ebay auctions on some CH670 horizontal shaft engines in early October. They had quite a few so I kept watching the auctions and each one sold for less and less and I finally bought mine for a little over $600 including shipping. I like the idea of a diesel conversion but it sounds like time is on your side. Chances are if you do some patient Internet watching you can replace your Kohler engine for less than you think this fall/winter. The great things about the CH Kohlers are that They all use the same basic block,if your JD uses the flywheel as a PTO drive with the stub shaft, they all are drilled and tapped for the shaft attachment, they all use the same wiring, so that's easy to decipher when it's time to splice your JD electrical plug on to it, and some of the JD mowers don't even use the engine crank/pto, but sounds like your mower does- there are tons of Kohlers spec'ed close enough to what JD used to easily make that aspect of the adaptation work easily.
 
 
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