Kohler 25hp Command Pro swap into 520-H

[IBleedRed 24]

 

I thought I would do a quick, but thorough, right up on my recent engine swap on my 520-H. 

 

The Onan has served me well for the past three year with the exception of the manifold leaking and having to run it at half choke to smooth out the idle. Currently this machine is used for my snowblower in the winter and loader in the summer. Knowing that the Onan had life left, but not wanting to risk catastrophic failure on a necessary piece of equipment I decided to look for a replacement. With shear luck I found a brand new 2001 Kohler 25hp on Craigslist for $450 and wasted no time getting it. The Onan will have a new home on a second 520 I was given in desperate need of attention, making it a good candidate for a restomod tower/ hood swap donated from a black hood model.

 

The swap isn't to terrible but more time consuming than I had originally thought. The worst of which was a wiring gremlin that I created running a wire to an accessory power source instead of a full time one. The engine is wider than an Onan making placement a challenge.

 

 

An inch froward of where the engine is currently bolted you can see two holes. The one to the left side of the tractor is a factory whole that I used for the first round placement of the motor. This left the engine to far forward for the clutch engagement to work properly, but was a good medium for the belt alignment. After moving the wholes back a little over an inch everything worked out great,  with exception of the belt guard which I have spaced out with washers for the time being.

 

 

Next came the wiring. With the diagrams I was able to find I discovered that the Kohler came with a similar setup to the Onan. This includes the oil pressure switch, starter solenoid, a place for the tach. wire. The Kohler has a fuel shut off solenoid that needs constant 12v while the engine is running and is tied into the starter solenoid. On the back of the engine plug there is a post with a red and a blue wire, the red one I connected to the yellow ( coil 12v ) wire and the blue one to the light blue ( starter solenoid ) wire. The fuel shut off is currently my only engine kill as the 520 key switch does not have a post that provides grounding in the off position. Here is the Basic layout:

 

Tractor                                                                 Kohler CH25S

Oil Pressure - Dark Blue                             Oil Pressure - Green

Starter Solenoid - Light Blue                       Starter Solenoid - Blue

Tachometer - Gray                                      Rectifier - AC Post

Coil Positive - Yellow                                  Carburator Solenoid - Red - formally connectedt to blue

Battery + - Red                                           Battery + - Heavy Red

Ground - Black                                           Ground - Black

Cylinder Temperature - White                    Temperature Sensor

                                                                   Kill Switch - White

 

The cylinder temperature probe needs a whole with 1/4 - 20 threads but the Kohler uses fine thread 1/4 so I had to tap one of the throttle bracket bolt wholes for it. this was the best location for a good reading while keeping it away from the exhaust port.

 

 

 

The throttle cables worked good, just had to shorten the choke a bit. The oil drain from the Onan was the perfect fit for the Kohler also. As for the pto I needed to bend the top bracket to allow the muffler to line up properly.

 

  

 

Last to be modded was the hood. Luckily the hood just clears the filter cover, but I had to notch for the muffler.

 

 

 

If anyone has any questions, don't hesitate to ask.

 

 

 

 

 

 

 

 

 

[Cable 168]

Excellent write up.  Appreciate your effort to share this change.

[slammer302 2,152]

It looks great to me. Thanks for the wiring info. I've wanted to do a similar swap in the future.

[AMC RULES 36,041]

Yeah...should be a nice upgrade there.   

[IBleedRed 24]

Yup, just waiting for the next big snow storm to give it a real test. 

 

Has as anyone heard of a break in procedure for these engines? Google didn't seem to know.

[cschannuth 3,761]

3 hours ago, IBleedRed said:

Yup, just waiting for the next big snow storm to give it a real test. 

 

Has as anyone heard of a break in procedure for these engines? Google didn't seem to know.

 

Whenever you run the engine make sure it is warmed up for a few minutes before running at full throttle and idled down for a couple minutes before turning it off. Both of those procedures will make that new engine last for thousands of trouble free hours. I would change the oil after the first 5 hours (some would say after 10) and then again after 25 hours. After that you should be good to go with normal maintenance. 

Edited January 15, 2017 by cschannuth
Clarity

[roadapples 6,971]

Guess that will make it a "525-H"  

[WildHorses 354]

What's the belt guard looking thing in the top final image? Is that a custom piece?

[dclarke 3,727]

Lots of good information here, thanks for sharing. 

[IBleedRed 24]

8 hours ago, danielbaute said:

What's the belt guard looking thing in the top final image? Is that a custom piece?

Not really sure what your referring to, but that bit on top of the muffler is just a heat shield. If I wanted to get away with out cutting the hood I could have cut that off instead.

 

[Tuneup 1,343]

Wow! Great job and with V-Twin torque, those rear tires and weight - she's an incredible puller. As for break-in, we all have our methods. It's my opinion that an air cooled engine has cooling capacity based upon full load. I would get the oil (basic dino oil) warm off idle and then run a good load like a deck for up to 30 minutes to stress the rings. After that, remove the load and run full throttle for max cooling for a minute then idle for 10 seconds to clear the muffler of un-burnt fuel if needed before killing it. My Kohler K301 rebuild had minor smoking from blow-by at the start but she was running clean after this break-in. So, there's some opinion on a Sunday for ya

[DougC 2,639]

Great job! Enjoyed your thread.  

[IBleedRed 24]

Thanks for all the compliments. I thought if nothing else I could save someone a bit of time on their swap.

[EricMassey 14]

Awesome swap! I'm wondering what size the front tires are and are they the v61's? If so I've been wanting a set for my 520-h but can't decide on the size. Thanks!

[IBleedRed 24]

V61 16x6.5-8's on the front, easily the best purchase for the tractor I've made so far. The tires plus the gear reduction makes it like power steering at half the cost. Even with the loader steering was a breeze. 

 

 

[bmsgaffer 2,040]

I just finished a swap into a 522xi with the fuel injected version of that exact same engine. I only have some minor exhaust routing modifications remaining. Awesome engines and it looks awesome stuffed under that hood. 

 

I had thought that Kohler twins were not rated for the PTO side-load and that's why many places were using the Briggs Vanguard for replacement. Any thoughts on that? 

 

Did I read you right that you were planning a black-hood swap? I had a plan like that for a while and never found time (then found and XI) so I sold the parts. That would be a sweet looking black hood, and I think they give just a bit more clearance for the muffler than the 520 hoods.

 

Have you tried fitting the chrome muffler shield from the 520? I think that would be the icing on the cake for that swap. 

 

 

[IBleedRed 24]

I know there's no bearings on the pto side of the engine, so that is a problem. It's a risk I'm willing to take for the circumstances. I'll keep updates coming if I see any premature wear.

 

I'm not sure because I haven't tried it yet, but I think I would have to cut the hood more to accommodate the heat shield. 

 

Here's the black hood swap:

 

 

 

 

[bmsgaffer 2,040]

On some of the briggs models wheel horse produced, they put a plate behind tne PTO with a thrust bearing on it to take the side pressure. I have never seen it in person, only read about it. This may be an option worth pursuing to prolong the life of that super nice engine... just a thought.

 

It may have only cost you 400 now but to replace it would be over 1000!

 

Oh i thoughtthe black hood was going on this kohler twin tractor, i misread.

[Northport 0]

My 416-8 needs a rebuild or repower.  I found a Kohler Command Pro 23hp model CH730 for $400.  Your swap documentation is very helpful, and it looks like this could work.  My biggest concern is the PTO.  The output shaft is 1 7/16, did you have to modify your PTO or crank, or did yours come with 1 1/8?  Any assistance is appreciated.

[IBleedRed 24]

I got lucky, mine matched the Onan. Not sure how to help in your situation, but I imagine someone has done a right up on it. Best of luck with your swap.

 

 

[19richie66 16,079]

2 hours ago, Northport said:

My 416-8 needs a rebuild or repower.  I found a Kohler Command Pro 23hp model CH730 for $400.  Your swap documentation is very helpful, and it looks like this could work.  My biggest concern is the PTO.  The output shaft is 1 7/16, did you have to modify your PTO or crank, or did yours come with 1 1/8?  Any assistance is appreciated.

Going through the same thing with the same motor. You can run an electric clutch as this motor is used on a Vermeer stump grinder. So far thats the only option I have found. 

[Northport 0]

I was also considering an electric PTO clutch,   I did find a write-up on someone who installed a similar motor on a Wheel Horse C160.  He had a machine shop cut down the shaft to 1 1/8, which is probably the most practical option.  He said they were able to do it while installed in the engine, but I'm guessing I'll have to remove it for anyone around here.

 

I did find that this motor is available with 1, 1 1/8, and 1 7/16 shafts, but the best I've found for a new 1 1/8 crank is $300 plus shipping.  I'm looking at a motor with 200 hrs, but don't want to spend a fortune modifying it. 

 

John Deere used the Onan's with 1 7/16 shafts, but their pto's are significantly different.  Good Luck

[19richie66 16,079]

good luck. Post back here if you find a good option. Mine won't be used for mowing so I only need the drive pulley on the engine at the moment. I have some ideas but nothing that wouldn't take some work to do.