Author Topic: Getting speed out of Drive Shaft Mowers?  (Read 205 times)

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Offline klett226

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Getting speed out of Drive Shaft Mowers?
« on: April 12, 2021, 10:26:54 pm »
Hey all! So I have been trying to do some research on being able to get speed out of a mower with a drive shaft rather than pulley and have found quite honestly very little on the topic. I have a Honda ht3813 I would like to build up but dont really know where to start other than larger tires and adjustment/removal of the governor, if that would even increase the speed that much. Any help would be appreciated.

Offline Knoot

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Re: Getting speed out of Drive Shaft Mowers?
« Reply #1 on: April 13, 2021, 01:54:45 am »
Others may be more helpful, but i'll try and answer.

Larger tires will help very marginally as far as speeding it up. If it's going 5 MPH right now, oversized tires might get you to 7mph. Removing the govenor is also a pretty bad idea on stock internals, these engines are meant to be run at 3600RPM. 3800RPM is probably safe, but anything over that is tempting fate, it also wouldn't get you that much more speed.

To get any real speed increase you either need to do one of these 4 things

1: Use a static gearbox to increase the rpm before the main gearbox on the mower. Downsides is that it'll be expensive, and reliability is a concern when you spin stock gearboxes much faster than they're originally designed to. This is a bad option unless you already have the parts readily avalible and you're comfortable designing, welding and fabbing parts.

2: Swap out the gearing on the original gearbox. Upsides is that it'll be a LOT cheaper, but finding the right parts and understanding the stock gearbox might be a little bit of a pain. I've never done this, but it's probably your best option, especially if you don't have a welder, shop equipment, and the knowhow to fab your own parts.

3: Buy a racing mower gearbox and fit it. Peerless gearboxes are the standard as far as I can see and come with the nice option of simply swapping pulley sizes to increase or decrease top speed. These are strong, but expensive, and you'll have to be comfortable with fabbing it in somehow. If you can do this, it's the performance but it won't be easy or cheap.

My advice, sell your honda. If it's in good condition it will get enough for a mower that you can more easily build. Look through the fourms for other builds for refrence. Anything with a decent transaxle and a belt pulley system can go 15-25mph for free with a pulley swap (front/back), or if you have to get new pulleys, they're readily avalible for under 20$.

Offline RoMow

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Re: Getting speed out of Drive Shaft Mowers?
« Reply #2 on: April 23, 2021, 08:09:22 pm »
Klett -- good post.  Knoot -- good answer, mostly.  Please allow me to "be more helpful:" 

   First, the engine: 
   You didn't say what engine was on your Honda HT3813 -- single or twin. I presume it's a Honda engine. 
   In February of 1999, I attended the Kohler Engine Level 2 Factory School, and on Thursday afternoon of the 5-day school, the class was given two Command 25hp V-twin engines to "do with whatever you'd like."  Since in our shops, we only see an engine needing repairs after it's been damaged, we decided we'd run one wide open and the other without oil.  For the wide-open engine, the instructor wired the governor open, set the engine stand outside (just in case), and started it up.  The tachometer read 5700 RPM -- for 45 minutes!  It never missed a beat, and would have run faster but the valve springs began floating, so 5700 was its maximum RPM-- well above the "recommended" 3600-3800 RPM.  And the short strokes of our mower engines do help keep metal stresses within limits. 
   So...with Honda engines being a comparable quality to Kohler, I wouldn't hesitate to do away with the governor.  Carburetor and manifold size, as well as the ignition system, will likely be the limiting factors on your RPMs. 

   Next, the transaxle: 
   Again, you didn't say what transaxle/transmission is in this mower, but I don't see a problem keeping the shaft drive and going with a Peerless 820 transaxle.  The heavy-duty 820 transaxle can be mounted "vertically" with the input shaft horizontal, axles at the bottom, and cluster gears above the differential.  There are also higher-speed final-drive gearsets available for the 820 that allow the axles to turn faster with no increase in input RPM.  What you would need to be careful about with this setup is how the transaxale input shaft disconnects from the driveshaft for the purpose of shifting gears.  And Knoot did have a good point about being able to vary pulley sizes for more ratio possibilities. 

   Again, I believe your "keeping the driveshaft" is doable.  If I can be of further help, please let me know.  The high-speed Gearset Upgrades are available on my internet store site -- . 
I also offer new 820 transaxles. 

   One thing is certain -- you would have one unique racer. 

   Decisions, decisions...

Rodney Rom 
   Kohler Expert Technician 
   Peerless Gear Master Technician 
Rom's Reworks 
Butler, MO 

"No matter how many material possessions or awards you may acquire in your lifetime, the only thing you will ever truly own is your reputation." (Age 73)