Hot Rodding my Push Lawnmower

volvoclearinghouse wrote:

gearheadE30 wrote: Noice. I just cranked the governor on mine. 5.5 hp factory, but 3100 rpm rating so that it's nice and quiet. I don't want quiet when the grass is long, because operating speed is basically torque peak. As soon as rpm drops, you're falling down the torque curve. Set to 3600 rpm, now when it lugs back, torque increases as it does so. Much, much harder to stall now.

From the HF cut-sheet, peak torque (6.6 lb-ft) is at 2500 RPM! Truth be told, I'm a bit wary of this engine to withstand high (over the 3200 RPM listed redline) RPM. For $99, we'll see how well it lasts. Also, interestingly, the oil fill is also the drain. You have to tilt the mower over to drain the oil out. That's, um, interesting.

I should probably clarify that I don't have the HF engine...it's a Kohler vertical shaft. Now that I've dug into it more, the 'recommended efficiency' governor setting is 2800 rpm, but the engine is rated to 3600 rpm. I was also surprised by the 9.2:1 compression ratio. Also, I actually couldn't find the torque curve for this engine, so I was basing everything on how it sounded.

I have since lowered it back to stock (which ended up being 2800 rpm ish), since I didn't wait a ridiculous amount of time to mow the lawn this week and it sounded a little excessive running that fast with that little load. Will probably settle at 3200-3300 next time I feel like fiddling with it.

bigdaddylee82 wrote: I did something similar a couple years ago, upgraded to a 190cc with electric start.

Retro-fit self propulsion? Any details on your set-up?

In reply to drainoil:

It was self propelled to begin with. Started life around 1998 as a 22" Huskee from Tractor Supply Co. Was a great mower, used hard, but maintained. The homeowner grade B&S engine on it, had worn the cylinder to the point of unusable. I don't remember the exact measurements but it was WAY over max spec.

While shopping for a replacement mower SWMBO mentioned that if she didn't have to pull start the mower, she'd happily mow the yard.

I could get an engine much cheaper than a new electric start mower, so I added this 190cc Briggs & Stratton from Surplus Center, and a "motorcycle" battery, starter solenoid, and switches from Amazon.

I went through a couple iterations of blade and drive pulley mounts.

While I made sure that the engine mounting pattern, shaft diameter, shaft thread, and shaft keyway on the new engine were the same as the old engine, I neglected to confirm the shaft lengths were the same. New electric start engine's shaft is shorter.

I first bought a taller MTD blade adapter that would fit the shaft and would get me close to the stock blade height, all while still allowing me to use the original front drive pulley apparatus that fit over the blade adapter. The new blade adapter wound up being tapered, and the big end was too wide for the pulley to fit over. I stuck the blade adapter in the lathe and turned it down until it fit. That failed shortly after putting the mower back into service when a large-ish clump of grass got hung up under the deck. I guess that blade adapter was tapered for a reason, and I removed too much material.

Version 2.0 of the blade adapter involved some keyed shaft stock from ebay, a keyed pulley from somewhere, the original blade adapter, a longer bolt, and some Loctite bearing retainer. I extended the shaft with a length of the bar stock, drilled a hole down the center of the bar stock for the blade adapter bolt, and slathered all mating surfaces with the Loctite. The original blade adapter was deep/tall enough to sleeve over where the new shaft extension meet the engine's shaft, so the Loctite was probably over kill, but I like my ankles just like they are, and don't need them amended in anyway by an escaped mower blade.

Version 2.0 has been in service since I built it, no issues.

I reinforced the deck with some strategically placed 1" angle iron welded to the top of the deck across the front, back, and along the side.

The battery mount, and switch mount are made from the same angle iron.

It obviously got painted too.

That's a lot of writing about putting a new engine on an old mower, but it really wasn't difficult.

My 22 inch craftsman motor died when I hit something I left in the yard and bent the crank. My dad gave me this beefy 7.0 hp craftsman mower with a rusty deck, so I swapped the motor to my much smaller deck. Now I don't need to mow the lawn very often as this mower doesn't mind how deep the grass gets lol

One thing to watch for- a lot of manufacturers are now listing small engines by their peak torque, rather than HP like in the old days. I'm not entirely sure why this is, but torque numbers are generally higher- i.e the 5.5 horse engine I bought has 6.6 torque (of whatever unit it is they use, not sure if it's N-m or lb-ft).

bigdaddylee82 wrote: In reply to drainoil: It was self propelled to begin with. Started life around 1998 as a 22" Huskee from Tractor Supply Co. Was a great mower, used hard, but maintained. The homeowner grade B&S engine on it, had worn the cylinder to the point of unusable. I don't remember the exact measurements but it was WAY over max spec. While shopping for a replacement mower SWMBO mentioned that if she didn't have to pull start the mower, she'd happily mow the yard. I could get an engine much cheaper than a new electric start mower, so I added this 190cc Briggs & Stratton from Surplus Center, and a "motorcycle" battery, starter solenoid, and switches from Amazon. I went through a couple iterations of blade and drive pulley mounts. While I made sure that the engine mounting pattern, shaft diameter, shaft thread, and shaft keyway on the new engine were the same as the old engine, I neglected to confirm the shaft lengths were the same. New electric start engine's shaft is shorter. I first bought a taller MTD blade adapter that would fit the shaft and would get me close to the stock blade height, all while still allowing me to use the original front drive pulley apparatus that fit over the blade adapter. The new blade adapter wound up being tapered, and the big end was too wide for the pulley to fit over. I stuck the blade adapter in the lathe and turned it down until it fit. That failed shortly after putting the mower back into service when a large-ish clump of grass got hung up under the deck. I guess that blade adapter was tapered for a reason, and I removed too much material. Version 2.0 of the blade adapter involved some keyed shaft stock from ebay, a keyed pulley from somewhere, the original blade adapter, a longer bolt, and some Loctite bearing retainer. I extended the shaft with a length of the bar stock, drilled a hole down the center of the bar stock for the blade adapter bolt, and slathered all mating surfaces with the Loctite. The original blade adapter was deep/tall enough to sleeve over where the new shaft extension meet the engine's shaft, so the Loctite was probably over kill, but I like my ankles just like they are, and don't need them amended in anyway by an escaped mower blade. Version 2.0 has been in service since I built it, no issues. I reinforced the deck with some strategically placed 1" angle iron welded to the top of the deck across the front, back, and along the side. The battery mount, and switch mount are made from the same angle iron. It obviously got painted too. That's a lot of writing about putting a new engine on an old mower, but it really wasn't difficult.

Thanks for the details, sweet set-up!