Scrubworks Fleet: Lawnflite 548 "Racing" Mower

[Scrubworks]

How cheap does something stupid have to be for you to rationalise that, while it has no reason to be in your life, you should just still buy it? Apparently, for me, it's £100. Which got me this:

This is a Lawnflite Model 548 mower, manufactured by the MTD company of Cleveland, Ohio, USA, so it's probably done more miles by sea than it has on land. It is powered by a 12hp Briggs and Stratton engine, has a manual gearbox, and a top speed of "light jog". A quick Google tells me these things were manufactured at the end of the 80s, which makes it even older than me, and a classic, even by car standards. I can't tell you exactly when this one was made though, because even though it does have a plate with "Date of mfg." on it, the machine or person in the factory that was supposed to stamp the date onto it missed the plate so badly that only the edge of one digit is barely visible right at the edge. It's that kind of quality manufacturing and high production standards that made America the industrial powerhouse it is today. Unlike more modern machines, this has no extras like cupholders, bluetooth cutting blades, or a radio, but it is almost entirely made from metal, excluding the plastic steering wheel and headlight lens.

Now, here's the thing; I don't actually need a mower. My lawn is barely big enough to require more than a stout pair of hedge clippers, so this would definitely be overkill. No, I bought this because, honestly, it seemed like a bit of a laugh. I've seen youtube videos where people modify old mowers to reach 50mph, and beyond. This really appeals to me. Of course, you can easily get that kind of speed out of a go kart, but you need a perfectly flat, smooth course to achieve that. This thing has the ground clearance (especially once I've binned the cutting deck) to deal with fields and muddy tracks and such like. There's also the ridiculousness of it. Go karts are fun, but they can end up being a bit serious. On the other hand, the idea of taking this little caricature of a tractor, designed for suburban dads to potter about their lawns with pride, and making it do highway speeds is hilarious. It's not meant to be fast; make it so. Also, proper go karts can be a grand or more. This was a tenth of that. It was actually up for £175, but the garden machinery dealer I got it from had taken it in part exchange a long time previously, and was glad to get rid of it I think. This will be a project of pure farce. I will absolutely be painting pride flags on it and covering it in meme stickers.

So, how do you get one of these things to go 50? Motorbike engine? Well you can do, but that's all a bit tryhard. It's actually much easier; you see, only about 1 or 2 of the 12 horsepower on tap is actually used to propel the thing around. The rest is used by the cutting blades. With them gone, your limiting factor is the gearing, which is of course very low. Fortunately, the actual gears that you select with the lever are all contained in a rear transaxle, like on a Volvo 300 series. The engine's crankshaft doesn't point rearward, as you'd expect in a car, but straight down towards the ground. The power is then transmitted to the blades and the transaxle through a series of pulleys driving rubber belts. That's where most of the gearing down is done, not at the actual gearbox. When you want to adjust the gearing of a car, you change the differential for one with a longer or shorter final drive. This is the same, but instead imagine the power goes to the diff first, then to the gearbox. By swapping the big pulleys with the little ones, you turn the gearing on its head. All that torque which was used to spin the blades is now available as power at the wheels. The belt and pulley system is alsos what makes these things so easy to modify. Engines-swapping a car is a big effort, with all sorts of considerations. Engine-swapping a mower is child's play. It's air-cooled, so there's no plumbing. The carb is gravity fed. The wiring is the starter and the ignition. Four bolts hold it in. Mower engines all use standard imperial size driveshafts, so all you need is a compatible pulley.

Before I do any of that though, there are some quality-of-life improvements that need to happen. As with any newly-acquired motor, it needs a service, probably quite badly. I also need to remove the lever throttle, and reattach the cable to a pedal with a return spring, just like in a car. The clutch and brake pedal also needs sorting. I say "pedal" because there is just one pedal that does both functions. The clutch isn't really a clutch like in a car, it's actually just a belt tensioner that, when pressed on, slackens one of the drive belts under the mower and prevents it from driving the transaxle. I'm fairly sure it's not actually needed for changing gear, even on the move, as all the gears in the transaxle should be in constant mesh with each other. We'll see. There's also an annoying switch that prevents you from starting the engine without the pedal depressed, so that will be bypassed. Only one of the headlights works, and it's about as bright as this whole idea. I'll probably put some LED elements in them instead, if not remove them entirely for some new lights. There's also a bit of slop in the steering. At 5mph this isn't an issue. At 50, it will be, so I'll have to address it. It also doesn't run that smoothly; it just about managed to drive itself into its storage spot behind my friend's shed. This is likely just a combination of old fuel and a dirty carb/air filter. A new sparky should also help.

We'll see how this goes. If it proves engaging enough, I might prepare it to enter some official mower racing events. If nothing else, it should just be a fun motoring project without the usual hassles and expenses of tax, MOT, insurance, or even using jacks or axle stands. You can literally just upend this thing or tip it onto its side to get at the underneath. Customers tend to object if you do that with their cars.

[Marshall2810]

Followed 👍

[Mally]

I sure there was someone on here into lawn mower racing at one time?

[Dyslexic Viking]

[tooSavvy]

WCPGW.... 😁👍

🚙💨

[Ian_Fearn]

I renovated one of these (mechanically), all parts are available too. Really good mowers, nothing like today’s junk and worth way more than you paid.

[loserone]

9 hours ago, Scrubworks said:

How cheap does something stupid have to be for you to rationalise that, while it has no reason to be in your life, you should just still buy it? Apparently, for me, it's £100. Which got me this:

You and I are on exactly the same page

[500tops]

Yeah, I'd be proud of thst

[Scrubworks]

5 hours ago, Ian_Fearn said:

I renovated one of these (mechanically), all parts are available too. Really good mowers, nothing like today’s junk and worth way more than you paid.

The main issue with mine is that the rear collection bag is missing, but that's obviously not an issue for me. The seller said that I'd probably get 80 quid or so for the cutting deck on eBay which would be a result. I don't know much about these things but applying the classic car logic of "older, simpler, metaller" seems to have worked.

[tooSavvy]

Id buzz round the empty carpark, on a Sunday, of any industrial unit *pref disused!

All Day..... 🚀

🚙💨

[Matty]

My mates eldest lad wants to get into carting. I've already recommended mower racing as cheaper to get into. Nice to see you back pal. Following.

[loserone]

Can you road register them? I'd love to take one over some of the local BOATs

[Scrubworks]

5 hours ago, loserone said:

Can you road register them? I'd love to take one over some of the local BOATs

It's possible I could register this as a mowing vehicle, I'm not too hot on the legislation for that. Honestly there isn't much point though. If this does end up being used on roads, it'll be briefly, on little country back roads where I won't cause any danger. To others anyway.

[catsinthewelder]

Our local mower racing scene seems to have died down now that the drivers are no longer allowed to drink before the races!  Was fun though, even in a wildly uncompetitive mower that would be on two or less wheels at times while heading down a field at 40+ mph.

Looks like a fun project 😎

[ETCHY]

On 18/12/2024 at 01:18, Scrubworks said:

How cheap does something stupid have to be for you to rationalise that, while it has no reason to be in your life, you should just still buy it? Apparently, for me, it's £100. Which got me this:

This is a Lawnflite Model 548 mower, manufactured by the MTD company of Cleveland, Ohio, USA, so it's probably done more miles by sea than it has on land. It is powered by a 12hp Briggs and Stratton engine, has a manual gearbox, and a top speed of "light jog". A quick Google tells me these things were manufactured at the end of the 80s, which makes it even older than me, and a classic, even by car standards. I can't tell you exactly when this one was made though, because even though it does have a plate with "Date of mfg." on it, the machine or person in the factory that was supposed to stamp the date onto it missed the plate so badly that only the edge of one digit is barely visible right at the edge. It's that kind of quality manufacturing and high production standards that made America the industrial powerhouse it is today. Unlike more modern machines, this has no extras like cupholders, bluetooth cutting blades, or a radio, but it is almost entirely made from metal, excluding the plastic steering wheel and headlight lens.

Now, here's the thing; I don't actually need a mower. My lawn is barely big enough to require more than a stout pair of hedge clippers, so this would definitely be overkill. No, I bought this because, honestly, it seemed like a bit of a laugh. I've seen youtube videos where people modify old mowers to reach 50mph, and beyond. This really appeals to me. Of course, you can easily get that kind of speed out of a go kart, but you need a perfectly flat, smooth course to achieve that. This thing has the ground clearance (especially once I've binned the cutting deck) to deal with fields and muddy tracks and such like. There's also the ridiculousness of it. Go karts are fun, but they can end up being a bit serious. On the other hand, the idea of taking this little caricature of a tractor, designed for suburban dads to potter about their lawns with pride, and making it do highway speeds is hilarious. It's not meant to be fast; make it so. Also, proper go karts can be a grand or more. This was a tenth of that. It was actually up for £175, but the garden machinery dealer I got it from had taken it in part exchange a long time previously, and was glad to get rid of it I think. This will be a project of pure farce. I will absolutely be painting pride flags on it and covering it in meme stickers.

So, how do you get one of these things to go 50? Motorbike engine? Well you can do, but that's all a bit tryhard. It's actually much easier; you see, only about 1 or 2 of the 12 horsepower on tap is actually used to propel the thing around. The rest is used by the cutting blades. With them gone, your limiting factor is the gearing, which is of course very low. Fortunately, the actual gears that you select with the lever are all contained in a rear transaxle, like on a Volvo 300 series. The engine's crankshaft doesn't point rearward, as you'd expect in a car, but straight down towards the ground. The power is then transmitted to the blades and the transaxle through a series of pulleys driving rubber belts. That's where most of the gearing down is done, not at the actual gearbox. When you want to adjust the gearing of a car, you change the differential for one with a longer or shorter final drive. This is the same, but instead imagine the power goes to the diff first, then to the gearbox. By swapping the big pulleys with the little ones, you turn the gearing on its head. All that torque which was used to spin the blades is now available as power at the wheels. The belt and pulley system is alsos what makes these things so easy to modify. Engines-swapping a car is a big effort, with all sorts of considerations. Engine-swapping a mower is child's play. It's air-cooled, so there's no plumbing. The carb is gravity fed. The wiring is the starter and the ignition. Four bolts hold it in. Mower engines all use standard imperial size driveshafts, so all you need is a compatible pulley.

Before I do any of that though, there are some quality-of-life improvements that need to happen. As with any newly-acquired motor, it needs a service, probably quite badly. I also need to remove the lever throttle, and reattach the cable to a pedal with a return spring, just like in a car. The clutch and brake pedal also needs sorting. I say "pedal" because there is just one pedal that does both functions. The clutch isn't really a clutch like in a car, it's actually just a belt tensioner that, when pressed on, slackens one of the drive belts under the mower and prevents it from driving the transaxle. I'm fairly sure it's not actually needed for changing gear, even on the move, as all the gears in the transaxle should be in constant mesh with each other. We'll see. There's also an annoying switch that prevents you from starting the engine without the pedal depressed, so that will be bypassed. Only one of the headlights works, and it's about as bright as this whole idea. I'll probably put some LED elements in them instead, if not remove them entirely for some new lights. There's also a bit of slop in the steering. At 5mph this isn't an issue. At 50, it will be, so I'll have to address it. It also doesn't run that smoothly; it just about managed to drive itself into its storage spot behind my friend's shed. This is likely just a combination of old fuel and a dirty carb/air filter. A new sparky should also help.

We'll see how this goes. If it proves engaging enough, I might prepare it to enter some official mower racing events. If nothing else, it should just be a fun motoring project without the usual hassles and expenses of tax, MOT, insurance, or even using jacks or axle stands. You can literally just upend this thing or tip it onto its side to get at the underneath. Customers tend to object if you do that with their cars.

Cool.

More pic's needed please.

[beko1987]

@Talbotis/was building/planning a Peugeot 306 powered lawnmower. That should do more than 50mph 😂

[Coprolalia]

On 18/12/2024 at 06:49, Mally said:

I sure there was someone on here into lawn mower racing at one time?

That was me. Let me find my OG post.

Edit:

Right back at the start of my main thread: 

20fucking17. We raced again in 2019. I have a mower sat in my garage awaiting building to regulations, but kids and house move have come first.

@Scrubworks - depending where you are there are a few clubs you can join to properly race. All have different rules about specs and modifications allowed.

The main one is the BLMRA. They're the oldest and have the tightest regs, so if you build to their spec you can race wherever. Their overnight 12 hour is a blast. Mainly SE UK, some trips abroad (Finnish ice racing). https://www.blmra.co.uk/ 

NWLMRA race in the North West. I've only raced in their stuff once (the  six hour). Don't know their rules. https://nwlmra.teamapp.com/?_webpage=v1

Mower madness are Wiltshire way. Much looser rules, and much more chill. http://mowermadness.club/DIARYP.html

Think there are others.

[High Jetter]

This has to be worth following. (Not on the road, obs)

[beko1987]

25 minutes ago, High Jetter said:

This has to be worth following. (Not on the road, obs)

If its built right and the mowing deck could stick out to the passenger side he could drive to work AND mow the verges 👌

[warch]

This is what I'm talking about.

Hayters gonna Hayte...

[Scrubworks]

4 hours ago, ETCHY said:

Cool.

More pic's needed please.

There will be more pics the next time I go and see it, which probably won't be until the new year. I asked my friend with his trailer to get us there for midday to pick it up, so naturally we arrived at 2pm. This is the only pic I took before we lost the light.

[Scrubworks]

1 hour ago, Coprolalia said:

That was me. Let me find my OG post.

Edit:

Right back at the start of my main thread: 

20fucking17. We raced again in 2019. I have a mower sat in my garage awaiting building to regulations, but kids and house move have come first.

@Scrubworks - depending where you are there are a few clubs you can join to properly race. All have different rules about specs and modifications allowed.

The main one is the BLMRA. They're the oldest and have the tightest regs, so if you build to there spec you can race wherever. Their overnight 12 hour is a blast. Mainly SE UK, some trips abroad (Finnish ice racing). https://www.blmra.co.uk/ 

NWLMRA race in the North West. I've only raced in their stuff once (the  six hour). Don't know there rules. https://nwlmra.teamapp.com/?_webpage=v1

Mower madness are Wiltshire way. Much looser rules, and much more chill. http://mowermadness.club/DIARYP.html

Think there are others.

Naturally the BLMRA were the top result on Google, so I read their regulations. It's fairly light as far as motorsport goes, but, in my opinion, still a little anal for a sport that they themselves describe as cheap and simple, and not to be taken too seriously. The requirement to haul your mower off to somewhere in Middle Earth to have it homologated seems a bit inconvenient. The pics and videos of their events show some pretty seriously worked-over machines, which seems to defeat the point of it being a cheap simple sport. I'm far more at the "fucking about" end of the spectrum, so Mower Madness seems far more my speed (literally). The NW lot might be a bit far away for me.

The whole racing thing is very much an end-game idea for me at the moment. The current goal is to get the mower to above Gee-Wiz speeds.

[catsinthewelder]

One thing you might want to investigate is a manual belt detensioner.  Sort of like a clutch pedal it lets you rev the tits off the engine then dump the 'clutch' for a quick start.  I would then wedge my foot under the pedal to stop myself from pressing it with the side bonus of holding me into the seat on bumps.  Other foot pedal was the brakes that I mostly did the same wedging my foot underneath!

Throttle was a bicycle brake lever on the steering wheel that was mostly clamped on full power.

 

[Scrubworks]

I went over to my friend's to work on the Lawnshite today.

Front left inner tube has deflated. Add to shopping list.

Main objective was to try and get it running more consistently. I only had limited time and no new parts, so this effort was limited to adding some fresh petrol, since it hasn't seen any in many months. Unfortunately, this did nothing. I'm not exactly sure what the problem is; the chap I bought it from said it probably needed a carb clean, and I'm inclined to agree with him. The symptoms are that it doesn't like anything other than idling at low throttle. Any throttle input, or attempting to drive it, will cause the engine to die, come back, and then die again, in a continuing, uneven cycle. It also doesn't particularly like hot starting, but starts absolutely spot on from cold, without any choke at all. This leads me to deduce it's running rich for some reason. Since the fuel didn't help, I swiped my friend's Parkshite socket set and started taking things apart. First thing, get the air filter off.

I was hopeful that it would be compeltely blocked, and that simply removing it would solve the issue. No such luck, it's in pretty decent shape. I did remove the foam pre-filter though, since this things of being showered in grass cuttings are behind it, and airflow for maximum race-winning speed is important. Without the filter, it did have an easier time hot-starting, but still ran like shit. I could actually see fuel pooling in the carb inlet, which isn't really a good sign.

Next, the sparky.

It's an NGK, and in pretty good nick. It also means that it's been changed at some point in the not too distant past, which is good as it means I now don't have to. It is, as you can see, rather sooted up, a telltale sign of running rich. Though, to be honest, I expect these get quite sooty in normal operation, since the engine doesn't really work up much of a sweat. I gave it a clean with a rag and stuck it back in. That also didn't really make a difference to the running, so, off with the carb.

Despite my earlier quip about this being poorly made, it's actually not. It's definitely built to last, as evidenced by a slightly excessive amount of steel covers and sound deadening foam in the engine bay, a lot of which I had to remove to get at the carb mounting screws. I found the shrivelled, roasted carcass of a small rodent in the cooling fins, which was lovely. You can just about see it in the picture, wedged under the ignition coil (or is it a magneto?). Some faffing later, and the carb was off.

The trouble is, the carb is a bit of a catch-22. Almost all my experience working with carburetted engines has been on classic British stuff, which all use SUs, or other variations of the variable-venturi design. I am very familiar with their issues, and how to identify and fix running issues. My experience with fixed-jet carbs amounts to a bit of faffing about with the Holley on my Mustang, which has plenty of Heath-Robinson mechanisms on it to elevate it above the controlled-leak quad toilet bowl it really is. The carb on the mower is of the fixed-jet variety, but it only has a single jet, and a simple throttle disc, and a choke disc, all fed by a little float bowl. That's it. The only thing I could identify visually that was wrong with it was that the throttle return spring was missing, which I suppose isn't much of an issue with a throttle lever, but going over to pedal I'll need to replace it. The catch-22 is that there's so little to go wrong with such a basic carb, which is good, but this of course means my running issue could very well be elsewhere. But, I mean, where could it be? The ignition coil could be faulty I suppose, delivering a weak, inconsistent spark, so that may need to be checked. All the other stuff that could usually go wrong doesn't apply here. There's no dizzy, advance system, overhead valves, or aux belts. There isn't even an oil filter. The charging circuit is working, as I can tell from the helpful little DC meter, which perks up when it's running, so hopefully that's not the issue. I'll clean and strip the carb, as much as I can, and try again.

[Scrubworks]

Was working on the thing and I couldn't keep this video out of my mind the whole time:

 

[Coprolalia]

On 19/12/2024 at 22:27, catsinthewelder said:

One thing you might want to investigate is a manual belt detensioner.  Sort of like a clutch pedal it lets you rev the tits off the engine then dump the 'clutch' for a quick start.  I would then wedge my foot under the pedal to stop myself from pressing it with the side bonus of holding me into the seat on bumps.  Other foot pedal was the brakes that I mostly did the same wedging my foot underneath!

Throttle was a bicycle brake lever on the steering wheel that was mostly clamped on full power.

 

Where were you racing @catsinthewelder? We ran a manual belt detensioner as a clutch for a long time. Easiest way, just mounted with a fuck off spring. I think most people have moved to motorbike/ cart clutches now.

This guy on YouTube has been documenting his builds and racing. He's ex motorsport journalist of some sort, so it's a high quality video (if a bit clickbaity on the titles).

https://youtube.com/@callumraces?si=mk0LTU9Hz2QBiZ6z

[Coprolalia]

Is it something simple like jets blocked up with shit modern fuel?

[Scrubworks]

Just now, Coprolalia said:

Is it something simple like jets blocked up with shit modern fuel?

I've disassembled the carb and cleaned the jet tube. It did seem maybe a little clogged but nothing serious. In the process of disassembling I discovered it actually has two separate mixture screws, so I will have a play with those when I refit it.

Also the mower does have a manual belt-detensioner clutch already, it's on the same pedal as the brake which I'd rather it weren't.

[RetroShite]

These are great fun to mess around with. We swapped pulleys and welded the diff on ours.

https://youtu.be/TEaGSuGvrWM?si=QmrJE9lvixt6tK_y