Introduction: Turn Old Walmart Briggs Mower Into Beastly Trail Mower



Action video: http://youtu.be/y8TV1NaiLzM  (sorry for the Blair Ditch Project quality video. hahhaa. I have plenty of trail to mow, so I will make another video, in daylight, and let you enjoy it later.) 

Action video showing carb adjustments on the lowest end Walmart mower (shown in last video)
http://youtu.be/Euq0pJWlmO8

I do volunteer work for a mountain bike club, and power equipment makes a major difference in the amount of labor needed to clear brush along miles of trail. I have used a conventional 2 wheel string mower with success, but found a way to make a similar device for cheap/free from salvage mowers. 

If you don't want to make a stringhead mower or brush mower from yours, this will still help upgrade your common walmart-issue briggs lawn walk-mower (use the steps you want). 

Warnings and disclaimers: 
If you don't know how to use welding equipment or sawzalls, get help from a pro. (a muffler shop will probably do it cheaply)
If you permanently modify your lawnmower, you are responsible for the results, and any breech of warranty, and your own safety. 
This modification does not make a mower into any kind of saw for cutting down trees! 
This is intended only for things you could normally use the mower for, but with benefit of rapid clearance of debris and easier pushing. This modification can make the mower less resistant to running over stumps and fixed objects, so caution and discretion must be used at all times! 
This modification will degrade the cutting quality of the mower for "manicure" yards and fine lawn grass, but will greatly enhance the ability to clear scrub brush, cacti, weeds, overgrown grass, vines, thorns, and small twiggy branches (up to 1/2" diameter woody plants, not trees!) There! 

I
f you use a sharp blade, this mows lawn grass ok. I mow my lawn with it. But if you beat up the blade on trail work, or use the string head, it doesn't cut as sharply and may make divots. Here's a pic of the old style LawnBoy mowers I got the idea from, but those usually had 2 stroke motors with not a lot of torque, and if I had one, I wouldn't sacrifice it for a trail mower. They cut grass nicely!

If you have a welder, you can weld a plate made from scrap metal (maybe which you cut off to open the deck) over the chute opening, which makes mounting the offset wheel a breeze, and eliminates the need for the flap which tends to hang up on stuff sometimes.

07/15/2013
Added photos of mower after braces added. I ran over a hard piece of wood, some kind of stick on the ground, and the blade jammed it against the little strap at the bottom of the mower chute. It still runs, but the frame was weakend by the broken metal strap and fatigued at the front where the wheel is mounted. I added these 3 braces made from scrap aluminum angle and 1/4" machine bolts. I tested it today and it worked as before, even stronger than the original, but the blade is a little warped. Still works though. I mowed a mile of grass with it. I will make another string-head from the busted blade.

Step 1: Create a "wingnut"/finger Screw for the Air Filter Box




Step 2: Replace Missing or Original Handle With Weighted Handle for Easy Starting and Safety

If a mower does not start when cord is pulled, it could "backfire", yanking the starter cord back into the reel. This is dangerous on any mower. Small handles make you grip harder, and can yank your hand before you can reflexively let go. A heavier handle may possibly be yanked, but will much more likely just drop down and hit the mower engine instead of stinging your hand. 
Still a good idea to round the edges and make the handle heavy. 

I made a weighted PVC starter handle to replace a missing handle and a screwdriver that was being used for handle on this junk find mower. (check Freecycle and similar programs to find "dead" mowers that often just need a little TLC or 1 part to run. Many of these mowers were $100-150 new and do not rate much when needing care, as shop rates are $50-100/hr. 

You can simply run the cord through the handle and tie it like a ski-rope, or drill a hole in the PVC and run the cord through it, tying a large knot by making duplicate knots or tying through a bead, and pulling the cord tight. It helps to loop the recoil cable around a stick or something while doing this, so it doesn't pull down into the starter housing! 

You will find the new, heavier handle with large grip area much easier and more comfortable to use than the standard handle!  
If you really want to get fancy, you can add PVC pipe caps. 

Make sure the recoil spring can contain the cord without the handle sagging, or use the handlebar eye-hook found on most mowers, to keep it near the operator. Mine sits by the engine cover and the spring holds it in place with no problem. 

If you know how to replace starter pull cables, now is a good time, before proceeding.  Make sure your cable is strong, because if it breaks the handle will fall off and the cord will suck into the starter reel. 

If you mow trails, you may need to start lots of times because of killing the motor to walk sections you aren't mowing, or to pick up debris, or for trail users coming by. 




Step 3: Replace Governor Spring With Solid Wire

I used a paperclip to make this item, which replaces the governor spring. This prevents engine surging or sputtering. This will allow the throttle speed to be retained, selected by the rotating throttle selector as on old-style mowers with variable throttle speed. The governor will still be intact (wind-vane type), but will not slow the engine beyond the speed selected by the throttle selector (you can install a $5 replacement throttle cable now if you have/ make a cable stop on the front of the engine's magneto cover.)
Warning: do not overspeed your engine or you could risk damage/failure. The governor will not speed UP the engine in this configuration, but will slow the engine as the throttle cable is relaxed or when the throttle selector is manually moved to low position. (stay away from the chute, and the rotating blades or strings!)
Set the paperclip linkage so that the max throttle setting is the max throttle speed that you ever wish to use (should match what the engine would surge to under load with governor spring originally). 

You can also use the original or replacement spring, and make a similar paper clip, but attached in a different place (there is a tab for it on the bracket or flywheel cover), so that it prevents deceleration beyond the RPM level stopped by the paper clip link (minimum throttle). 

Note how the paperclip has  a u-bend which holds the round shape in the governor linkage, but allows it to freely move forward. 
Note how the paperclip link installs first into the round hole, then into the selector arm. I recommend needlenose pliers for making this adjustment. 

Be sure to test and confirm this setting before further steps. Be sure the selector arm can activate the linkage without jamming or losing the paperclip. 

Added: If you have access to bicycle cable cutters and soldering supplies, you can make a really nice throttle cable from a bicycle friction shifter (mount under handlebar, to not affect the deadman's clutch), which can act as a thumb throttle or a selectable lever. 
run the cable to one of these points and bend the cable in a loop through the proper hole in the selector arm. Wrap with copper wire and solder to anchor it. The cable pull will accelerate the engine.  

Step 4: Modify the Deck for Maximum Clearance to Prevent Stalls and Clear Debris

(more photos later) This is the hardest step. This can be done most easily with a cutting torch, like my last one. (got a mechanic to do it for $10)
You may resort to using a sawzall. On really heavy duty old decks, it will be a MAJOR chore, and might require removing the engine to maneuver and place the deck for sawing. If using welding equipment, drain and dry the gas tank and be sure not to burn the spark wire off. 

See warnings in post 1!  Do not remove metal from above the corner of the metal deck where the top of the bowl meets the front face of the deck. If you can help it, leave a 1/2" "lip" under that corner for deck strength. Some mowers have a ring of sheet metal tacked onto the stamped steel deck, and it may become dislodged or get in the way of a saw blade. Most of these mowers have a 1 piece formed deck that is no problem. 

Before cutting, remove the left front wheel and wheel adjustment assembly, and SAVE these components. 

After cutting off the unwanted metal, you will have to drill a new hole (or 2) to replace the left front wheel (and wheel adjuster if you have one). The mower may flex some now, so I recommend drilling so the wheel system will RAISE the deck 1/2 " higher than the rest of the wheels to compensate. (the wheel may run at a slight angle when the deck flexes. It's ok. But you can weld in a shelf bracket or similar piece of steel to reinforce the deck, if you want. )

IF you use this mower now with a blade, instead of a 4 string head, you must be very cautious not to hit pipes, stumps, large rocks, or fixed objects that would normally possibly just stop the mower. (do not warp your blade or crankshaft) If you use a blade, and mow a normal lawn, the blade can make small divots at low height settings, if the mower front left wheel goes in a shallow area or the mower is bouncing. I have used one of these with a blade and it can easily clear 5 foot tall grass, but you must walk the yard carefully first to pick up any objects that can be struck or thrown. That's good practice for all mowing even with string trimmers. 

With a string head, these problems are still possible, but most likely you'll just break off the string and have to kill it to change strings. 

Step 5: Replace the Blade With a Fixed String Head

(more photos coming)

Note, with 3 to 5hp, you can run as thick a gauge of line as you care to. The minimum needed is .130! ! ! I recommend .155 or .170, or if you can spend it, that "flexiblade" is unbelievable for cutting power and almost indestructible. I've used the flexiblade string and it's wicked, but it's expensive and only works in quick-change type heads with ratchets. 

There are several ways to do this. You can buy a commercial fixed  "4" string head for brushcutter mowers (about $30), that fits the blade fixing bolt you have. You may have to remove the blade-to-crankshaft adapter and attach it to the bare shaft (not recommended, but it works well, just has less strength than other options). You may need a longer bolt. You may need to find or fit a washer to adapt the string head to mower shaft. Most likely the kits with multiple washers will have yours. 

If your mower has a blade-to-crankshaft adapter with a large flat "washer" on the bottom, this works great to just bolt a commercial fixed-head to it. 

You may also find some quick-detach fixed string heads (2 strings) that bolt up easily to the bare shaft and protect it (they will place the string path higher in the deck, note). These are great, as they allow you to use less string, and make string changes a breeze. 

You can also MAKE a four string head from a worn out blade (labor intensive). 

You will need to remove the blade, clamp it in a vise, and saw off the ends/wings (keeping 5" of the center piece), grind smooth and round the edges, and drill in the pattern shown or similar, to attach the strings. Chamfer the holes to prevent cutting the strings with centrifugal forces. 

You could also MAKE a four or eight string head (leave short strings on and add new ones to opposite sides) for maximum cutting potential.  Draw a 5" circle on a piece of 1/4" plate steel, cut out the circle, drill central hole, check object for balance as a flywheel, and drill pattern for strings. 

Do not make it out of wood. I tried that, and it worked, but the holes wore out and eventually it broke. I made one before with a commercial aluminum fixed-string head and it worked well. 
examples, with many similar products available. 


Oregon brand string head $30 with adapter washers and nuts http://www.amazon.com/Oregon-55-130-Trimmer-Head-Fixed/dp/B0018U2CWU

Echo Rapid Loader head from Home Depot $30  http://www.homedepot.com/p/ECHO-Rapid-Loader-Trimmer-Head-21560059/100056334

Oregon Jet Fit Flexiblade compatible 4 string (the ultimate) $60 http://www.lawnmowerpartsoutlet.com/Oregon-Aluminum-Jet-Fit-Trimmer-Head-4-Line-55-404_p_4677.html

WARNING: Obviously, you will need to kill the mower to change strings. 
Note: You cannot use this modified mower to trim lawns as a trimmer for cutting up to fences and bricks. The wheel gets in the way. You need a conventional string trimmer (portable or wheeled) for that. This is for beating down hiking/biking trails and overgrown lawns. 

Step 6: Install and Trim Line, Test Run Mower

I prefer .155 line, and it is hard to cut with pocketknives or scissors. You can use these pet nail clippers (about $5) as a pocket or backpack carry tool to cut line rapidly. I like to make duplicates of the line pieces I need (pre-cut pieces) from a large spool at home, instead of buying pre-cut pieces (expensive and wasteful). 

The edge of the front right wheel well can be sharpened to cut string by rotating action, but it's harder on your line head, and can THROW pieces of cut line!  I would rather pre-cut my pieces, or install from a long piece and cut to fit. 

This mower may THROW objects, like any string strimmer, and caution should be used, and protective equipment worn. 

Joey Novak has made a more heavily modified mower that uses manufactured trimmer string heads on a mower shaft, with a similar engine. You can also view his IB page https://www.instructables.com/id/Hack-a-Mower-to-build-your-own-Red-Neck-Trimmer-Mo/ . 

My "mauger" is more suited to my work because it still has 4 wheels. Mine requires a lot of maneuvering over rough terrain, including hills, and sometimes the blade is needed for things that nylon string will not cut. 

Comments

author
Yard Sale Dale made it! (author)2015-02-17

This went ok until the engine died. It was a trash find, anyway, and survived hard use, so I do not care.
I made a different bush-mower, later, which is still in use, and which has outlasted a couple junkyard engines. It's ugly as heck, and only mows at one (tall) height, but it does the job (knocking down grass on footpaths). The big wheels are in front because it does not need to turn sharply or often, and it rolls over obstacles and tree roots.

scorpion mower 1.jpg
author
Yard Sale Dale (author)2013-06-22

I did this before with a heavy 1970s dept. store mower. It worked very well, but the motor was old and died. The walmart Weedeater mower shown is pretty weak. I had to add 2 braces to the top of the deck, by bolting pieces of angle extruded aluminum to it, for strength. The strap at the bottom of the grass chute got knocked out by a chunk of wood, so I have to add a piece there too probably. It's still running like a champ, though. I've mowed miles (literally, the trail is 6mi long, and I've been over it a couple times) with it and it plows down years-old thorn bushes, vines, saplings, deadfall, leaves, thick weeds, and dirt! It's very useful for "shaving" the edges of the foot path where they have grown deeper from high foot traffic and rain. If you make one of these with a 5.25 briggs, it should be unstoppable! That will be heavy, though, so I recommend bolting the wheels straight onto the deck instead of the adjustable casters, (re-use your wheels if you want), and bracing the deck. Old Snapper decks are the boss, and have a 5 speed self-drive with current parts available.

author
telmore1 (author)2016-03-03

im thinking of making a bush mower but instead of pushing it I will pull it behind my off roading mini bike just have to come up with a hitch please help any tips or ideas

coleman mini bike.png
author
dq3221 (author)2013-11-28

A Trimmer mower is similar to a regular mower but is much better for cutting tall weeds. A regular mower just runs over them, pushing them down and out of the way of the blades.

author
Yard Sale Dale (author)2013-08-25

I recommend finding a longer bolt for the air-cleaner, and leaving it threaded in, and use a nut, if you want to remove the filter a lot of times. The plastic in the carb stripped out on this one. I will include an update on how to make a permanent air cleaner stud and mount it to the side of the carb. (bent piece of 1/4" all-thread, with a few nuts). If you want a whole new mower for $80 or less, check on fleabay. Here's a classic briggs pusher for $80 shipped! http://www.ebay.com/itm/Murray-22-Push-Gas-Walk-Behind-Lawn-Mower-Briggs-Stratton-Engine-M22450/360722167148?rt=nc&_trksid=p2047675.m1851&_trkparms=aid%3D222002%26algo%3DSIC.FIT%26ao%3D1%26asc%3D163%26meid%3D832117923481450308%26pid%3D100005%26prg%3D1088%26rk%3D3%26rkt%3D4%26sd%3D130972366616%26

author

This deck has finally had it after mowing a cow pasture (2.5 acres) with it. hahaha. I'm putting the engine on a converted bicycle trailer lawn mower. (see on youtube bicycle drawn lawn mower, instructables later. Friend is welding the engine mounts, and I've got to get a couple more pieces of tin to finish the "deck". We're going to use it to mow where a yard tractor can't get in, on a bike trail that is basically a flat road )

author
Yard Sale Dale (author)2013-08-18

The old junker is still running well, but the deck has been beaten mercilessly (rough mtn bike trails, cracked ground, and even dog pens and horse pastures, plus that stump I hit last month, oops), and has cracked again. The Weedeater deck is the flimsiest deck I've ever seen. The points the engine bolts through are reinforced with 1" squares of steel plate. lol. I think I'll bolt another piece of flat stock to it to fix it until I find a high-wheel deck from the 1980s (one of those that is hard to dent with a hammer even). Check your local junkyard or scrap yard. Millions of mower decks in USA will take Briggs 3 bolt motors.

author
joeynovak (author)2013-06-25

Awesome build Dale! Much safer then mine. I like it!

author
joeynovak (author)joeynovak2013-06-25

Also, building your own trimmer head definitely reduces the cost. I had problems with mine backfiring after a lot of usage, I thought it was because dust was by-passing the air filter and had worn out the valves, it seems you're saying that without the weight of the blade it may backfire more often, is that right?

author
Yard Sale Dale (author)joeynovak2013-06-25

If you mean during starting, yes. The weight of the flywheels on typical mowers is designed to work with lawnmower blades as an additional weight. It's like the crank handle on old timey Ford cars. If you spun it but not hard enough to start the engine correctly, the handle could spring back and turn you! Sometimes those engines could be started backwards, but the mower can not because the pawls on the starter reel and tension of the starter rope prevent it. I had a junkyard find mower that backfired with a standard blade on it (crappy carb and worn valvetrain), and it stung my hand so badly I thought I had a broken knuckle. It went numb and swelled like a tennis ball. Be careful.

author
joeynovak (author)Yard Sale Dale2013-06-26

Yeah, during starting. Thanks! Again, awesome build!

author
Yard Sale Dale (author)joeynovak2013-06-25

If you mean backfiring during operation, most likely it's a dirty plug, dirty governor/linkage (don't forget the pivot the carb butterfly sits on) clogged or burnt muffler/screen, or deformed timing key. Check the easy ones first.

author
Yard Sale Dale (author)joeynovak2013-06-25

Thanks. I like yours better, but I'd make a string head out of a steel disc for it, and use a high-wheel mower for the deck. A removable bar with a swivel caster on it for the front might help when cutting lawn grass with it for the regular haircut. A 2" wide wheel won't block up the grass going into the strings. Might be a PITA on hills though. I have to wrestle my 2 wheel conventional trimmer on hills.

author
Yard Sale Dale (author)2013-06-01

This worked great. I mowed the heck out of miles of grass and thorny stuff. The left wheel pointing in just a bit did what I expected. It helped a lot when mowing on inclines and deflected a lot of vines and roots instead of hooking them behind the wheel.

author
Yard Sale Dale (author)2013-06-01

I drilled two holes in the side of the tube, about 1/2 inch apart, and looped the string through them to tie. I like this better than the ski-rope style tie.

author
Yard Sale Dale (author)2013-05-31

I recommend removing the spring, and using a throttle wire. If you use a non-solid cable, you may have to add a strong spring to pull back the throttle selector when cable is relaxed.

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