Hot Rodding my Push Lawnmower

With a little over 3 acres, barns, a garden, woods, etc., we sometimes need something like a small brush hog for dealing with problem areas (i.e. stuff I can't get to with the tractor, and hence doesn't get mowed regularly). We do have a little 4 HP Murray, and a 3.5 HP of some unknown make, but they get bogged down easily, and the decks are rusting and falling apart.

A friend of mine gave me a bare deck that looked nearly new; he'd picked it up from someone who'd run the engine out of oil.

Then these went on sale for $99 at my local store.

I robbed the throttle cable, blade mount, and some other small bits off the 3.5HP mower. Then I bought a new universal 21" blade from Home Depot ($18) The result:

With 5-and-a-half romping, stomping horses, it really cuts the grass!

Compare to this, basically the same result for $100 less. Total extra time investment was about 45 minutes to install the engine- really, it just bolted on perfectly.

You built the Shelby Cobra of push mowers!

Next step, remove the governer!

bearmtnmartin wrote: Next step, remove the governer!

It is adjustable on this motor...

volvoclearinghouse wrote:

bearmtnmartin wrote: Next step, remove the governer!

It _is_ adjustable on this motor...

Just don't get too aggressive on the blade pitch:

In reply to slefain:

Wow. That thing flies!

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

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.

Here I was hoping to see a chopped and turbo'ed lawn tractor

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.

Go big or go home!

volvoclearinghouse wrote: Go big or go home!

Hmmmm. I've got a woefully underpowered 52" walk-behind that will probably need a re-power at some point. That engine would be more than I spent on the entire mower though.

I forget why, but I want to say spinning a 21" mower blade that fast isn't safe for some reason.

When I was a kid I hot rodded my Mom's old riding mower.

I could ride wheelies on that thing for over a block.

Moriarity over on the HAMB board has a hot rod lawn mower.

slefain wrote:

volvoclearinghouse wrote:

bearmtnmartin wrote: Umm, properly installed blade creates down force. wonder how they got that thing to fly. I suspect trickery Next step, remove the governer!

It _is_ adjustable on this motor...

Just don't get too aggressive on the blade pitch:

PO of our house left their 6.25hp craftsman mower behind. The motor looked darn near identical to my 4hp craftsman motor, I almost swapped the big motor onto my deck but ended up selling the mower they left behind last weekend. It ran ok but did not look like it was taken care of at all. Also appeared it may have had a significant oil leak.

stuart in mn wrote: Moriarity over on the HAMB board has a hot rod lawn mower.

Yeah, but that guy has an Ed Roth fetish, so it's to be expected.

LSx that biotch!

There's a Kohler engine dealear near me who put a 18hp v twin on a push mower as a bit of a promotional piece.

Without mufflers that thing is nearly Harley loud.

SVreX wrote: When I was a kid I hot rodded my Mom's old riding mower. I could ride wheelies on that thing for over a block.

Zoomies and wheelie bars?

Is it possible to adjust the hydrostatic drive on a yard tractor mower so it gets more speed? The logical next step after that is a small turbo...

Nitrous or go home.

I've built a couple of "easy" go-karts...the bones for each was a $100 used lawn tractor, the sort with a simple belt drive front to back, and a vertical shaft engine. Go down to your local small engine store with the shaft diameters of the engine and the transmission input, and buy whatever ratio of pulleys gives you the speed/ acceleration you want. Put the big pulley on the engine and the little one on the transmission, adjust the clutch accordingly, strip off all unnecessary weight, and go have fun.

The second model I built was so stripped down it had no battery or starter. I would put the tractor in gear, push it until it fired, and jump on. That thing would do about 30 mph- pretty frightening. Make sure the front wheels have some toe-in.

edwardh80 wrote:

SVreX wrote: When I was a kid I hot rodded my Mom's old riding mower. I could ride wheelies on that thing for over a block.

Zoomies and wheelie bars? Is it possible to adjust the hydrostatic drive on a yard tractor mower so it gets more speed? The logical next step after that is a small turbo...

Nope- no wheelie bars. It was strictly a balancing act. Hold on, and try not to soil yourself.

Most of the kids in my neighborhood had taken a pretty hard landing on their azz at some point.

Thank goodness Mom never knew!

That thing is begging for silver racing stripes!