How does pulling a string start a lawnmower or a weed eater?

[sbrothy]

I simply love how you people can get a 50 message thread out of how starting a lawnmover works! I really feel i found my tribe!

 

[jedishrfu]

A great (but infuriating) character. The book was really fab. The film was good for its generation, but needed a plot twist to avoid the fact that their plane crashed after takeoff during the filming and there were deaths but no money to make another plane.

Wow, I didn't know about the plane crash and deaths. I'll have to read more on it.

While not common, it did happen in many movies like Charlton Heston's Ben Hur and the chariot race. Perhaps that's why actors get such high pay for hazardous duty. Over the years, I've heard so many of these stories.

 

[Janus]

Aircraft required reliable spark-ignition piston-engines. Magnetos and spark plugs were critical components, so they were duplicated, and always operated in parallel. The duplicate circuits were not engaged one at the time, so much as disengaged one at the time.

Both magneto circuits would be enabled, except during the power test before takeoff. Then each magneto on the aircraft would be disabled sequentially, and the drop in RPM of that engine noted. If that "mag-drop" in RPM, fell by more than the specification, the flight would be aborted, because the other magneto circuit was faulty.

Once, while on a training flight with my instructor, we suspected that we had lost a magneto, but after landing, we checked everything out, and couldn't find an issue. The instructor reported it to the airport mechanic so they could give it the once over to make sure.

 

[sophiecentaur]

I'll have to read more on it.

The wiki article mentions it.

 

[JT Smith]

I don't think we can have all of these diversions without at least mentioning how retractable pull cords in lawn mowers, vacuum cleaners, etc. sometimes stop retracting easily/reliably.

When I was about ten years old I decided I would fix the pull cord on our Briggs & Stratton lawn mower. I had tools. I took it apart. At some point I got to the coiled spring and when I pulled it out it inflated in way that Alan Guth would have been proud to have witnessed. Needless to say...

 

[jedishrfu]

That's got to be a dangerous activity pulling out a loaded spring. Mechanics risk their lives when replacing springs, shocks, and other loaded devices. One wrong move and the thing will slip with tremendous force.

 

[Averagesupernova]

That's got to be a dangerous activity pulling out a loaded spring. Mechanics risk their lives when replacing springs, shocks, and other loaded devices. One wrong move and the thing will slip with tremendous force.

There's typically not a lot of torque on a recoil starter assembly for a lawnmower. Not to say the spring can't get away and maybe give someone a good startle. Doing real physical damage will likely not occur unless it gets to an eye. I've had many of them apart. If it's just a broken cord there is usually no reason to disassemble to the point of dealing with a spring.
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The real danger in springs working on vehicles and such is suspension. Semi trucks use air brakes and the canisters that actuate the brakes can have a spring. They will be a two chamber canister. One chamber activates the brakes when air is applied. The other releases the brake when air is applied. That one functions as a parking brake and is the one with a spring. People have been killed messing with those not knowing the dangers.

 

[Baluncore]

People have been killed messing with those not knowing the dangers.

Above all, recognise and identify stored energy, lest it will destroy you.

 

[sophiecentaur]

There's typically not a lot of torque on a recoil starter assembly

Above all, recognise and identify stored energy, lest it will destroy you.

Precisely. It's Energy wot does all the damage. The torque on the starter assembly has to be low enough for your (fit) granny to start the mower or you'll need to be doing it yourself.

The most comical pull cord starting process is with an old outboard motor on a small boat. The skipper can get very cross.

 

[JT Smith]

That's got to be a dangerous activity pulling out a loaded spring. Mechanics risk their lives when replacing springs, shocks, and other loaded devices. One wrong move and the thing will slip with tremendous force.

The problem was that there wasn't enough stored energy to pull the flimsy cord back in. My plan (I was ten years old) was to wind it tighter.

Our old vacuum cleaner has the same problem. I'm not going to try and repair it but I'm not afraid of it.

 

[Averagesupernova]

The problem was that there wasn't enough stored energy to pull the flimsy cord back in. My plan (I was ten years old) was to wind it tighter.

If you are ever in that situation again:


Notice the notch. Line the notch up next to where to cord goes out and slip the cord in the notch and wind around tightening the spring by one turn. You will obviously need to have enough cord out to get a full turn. No need to disassemble any farther than the pic shows.
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Oh btw @JT Smith, you're excused for not knowing. Lol. Any ten year old that wants to be doing 'stuff' like that instead of being a bum gets my approval.

 

[JT Smith]

If you are ever in that situation again:

View attachment 360702
Notice the notch. Line the notch up next to where to cord goes out and slip the cord in the notch and wind around tightening the spring by one turn. You will obviously need to have enough cord out to get a full turn. No need to disassemble any farther than the pic shows.
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Oh btw @JT Smith, you're excused for not knowing. Lol. Any ten year old that wants to be doing 'stuff' like that instead of being a bum gets my approval.

Thanks but I'm never going to try to repair a gas powered lawn mower again. We got rid of our lawn a long time ago in favor of ground cover that didn't require any watering. And our tools now are electric. I think that is now mandated by law here. It turns out all those lawn mowers and leaf blowers produced a substantial amount of pollution, way more than I would have thought. So good riddance to those Sunday sleep disturbers.

And I'm okay with my ten year old self, at least in that way. Around the same time I tried to fix a radio and when I plugged it in to test my work it burst into flames! That was more spectacular than the near-instantaneous expansion of that spring.

More recently I tried to fix a fancy microprocessor controlled toaster. No flames that time but there was smoke!

 

[berkeman]

Around the same time I tried to fix a radio and when I plugged it in to test my work it burst into flames!

Bonus Points!!

 

[jedishrfu]

I did something similar. Not having enough allowance to buy relays for a mechanical digital computer and not understanding the AC in AC electricity, I embarked on a journey to create my own. I collected some 10-penny nails and began to wind wire around each one to form a sort of line of relays. I used tin cut from discarded cans for the switching contacts.

I figured that since it was 120v, I only needed about ten windings to complete my electromagnet using thick electrical wire that I found in the garage.

I plugged the two wires of my first relay into the socket as a test and was startled by the flash of light and the melted wire. I judiciously yanked them out of the socket and spent an hour or so replacing the blown fuse and checking every appliance in the house to reset its clock.

However, there was one clock in my parents' room that I missed but my mom didn't. Grounded for the sake of STEM learning.

 

[JT Smith]

Not nearly as advanced as you but I tried to make an electric hot dog cooker: two nails though a piece of wood and an extension cord. You get the picture. When I plugged it in the hot dog shivered for a second or two and then that was it. That circuit in our garage never worked again. We had breakers instead of fuses but resetting the breaker didn't make any difference. I wonder what my ill conceived idea did to that circuit?

 

[Baluncore]

The most comical pull cord starting process is with an old outboard motor on a small boat. The skipper can get very cross.

The chief engineer then has to go through a long checklist before finding the problem and fixing it. That requires a thorough understanding of small engines. Is there a spark? Does it have clean fuel? Is it flooded? Does the camshaft rotate? Does it have compression? Is the air filter or the exhaust blocked? Does the starter turn the engine in the correct direction? Trying to start a small engine goes on, as long as the engine does not, and your arm hurts. Messing around in boats is such fun.

 

[sbrothy]

OK then. Let me join in the geeky fun:

Starting a Wankel engine (rotary design) should be easier or smarter somehow. Lots of factors at work:

Optimization design of the ignition system for Wankel rotary engine considering ignition environment, flow, and combustion

Also, I'd never heard of the The Lawn Mowing Problem.

 

[sophiecentaur]

Also, I'd never heard of the The Lawn Mowing Problem.

I'd guess that it's rapidly becoming a thing of the past. Cordless mowers are less smelly and batteries are not a ridiculous price any more. Larger IC mowers will have electric start (for the same reason) just as motor bikes have electric start these days.

It's a shame that people are switching to low maintenance plastic 'grass' even for massive areas of lawn. One of my sons has a lot of money and switched for reasons of fashion.

 

[sbrothy]

I'd guess that it's rapidly becoming a thing of the past. Cordless mowers are less smelly and batteries are not a ridiculous price any more. Larger IC mowers will have electric start (for the same reason) just as motor bikes have electric start these days.

It's a shame that people are switching to low maintenance plastic 'grass' even for massive areas of lawn. One of my sons has a lot of money and switched for reasons of fashion.

Not directly lawnmower-related, but:

Yeah, that last thing sounds kind of sad. And yeah, batteries are the future for sure. Just compare the smell of the inner city streets now to how they smelled in (y)our childhood. I'd certainly call that progress.

 

[sophiecentaur]

Not directly lawnmower-related, but:

Yeah, that last thing sounds kind of sad. And yeah, batteries are the future for sure. Just compare the smell of the inner city streets now to how they smelled in (y)our childhood. I'd certainly call that progress.

Are you referring to the smell of horse manure? You can’t be that much older than me.

 

[Janus]

I did something similar. Not having enough allowance to buy relays for a mechanical digital computer and not understanding the AC in AC electricity, I embarked on a journey to create my own. I collected some 10-penny nails and began to wind wire around each one to form a sort of line of relays. I used tin cut from discarded cans for the switching contacts.

I figured that since it was 120v, I only needed about ten windings to complete my electromagnet using thick electrical wire that I found in the garage.

I plugged the two wires of my first relay into the socket as a test and was startled by the flash of light and the melted wire. I judiciously yanked them out of the socket and spent an hour or so replacing the blown fuse and checking every appliance in the house to reset its clock.

However, there was one clock in my parents' room that I missed but my mom didn't. Grounded for the sake of STEM learning.

Tried to make a model electric motor from instructions given in a book. Hooked it up to the 6 volt lantern battery it was supposed to run on, gave it a few test spins and nothing. Assumed it wasn't getting enough juice, so dug out an old electric cord, wired it up and plugged it in. gave it a spin.... shower of sparks and a blown fuse. My folks weren't pleased, but nothing to the level of grounding me.

 

[sbrothy]

Was probably just a fuse or two. But you learn something you can't learn any other way. Like lifting a cat by the tail.

EDIT:
Oh the fuse. You said as much. Was a little too quick there...

 

[sbrothy]

Are you referring to the smell of horse manure? You can’t be that much older than me.

I'd almost risk my neck and postulate that the smell of manure was probably healthier, heh, perhaps even more pleasant. With engine exhaust you can pretty much smell it's carcinogenetic properties.

Like you know the smell of a solvent (one of the stronger ones obviously) isn't healthy at all. Like the smell of gasoline or kerosene only worse.

EDIT:
Like salmiak spirits for removing traffic film from windscreens. That one is nasty on more than one social level / context. .. errr, sadly.

 

[gmax137]

but nothing to the level of grounding me.

I see what you did there

 

[JT Smith]

I'd almost risk my neck and postulate that the smell of manure was probably healthier, heh, perhaps even more pleasant. With engine exhaust you can pretty much smell it's carcinogenetic properties.

Like you know the smell of a solvent (one of the stronger ones obviously) isn't healthy at all. Like the smell of gasoline or kerosene only worse.

While I agree with you that engine exhaust is most likely a lot more hazardous than the smell of horse poo I don't think it's something we instinctively sense. I grew up around horses and smelled (and shoveled) a lot of it. We used it in the garden as fertilizer. I didn't particular like the smell. I actually did like the smell of cigarettes and also gasoline. I still prefer those aromas to horse manure. I know (or at least believe) that horse dookie is okay to smell, handle, or grow your vegetables in whereas cigarette smoke and gasoline fumes are things to avoid not because of instinct but because I was taught that.

Frankly, if any smells are instinctively repulsive I would imagine that feces would be high on the list.

 

[DaveC426913]

I didn't particular like the smell.

Frankly, if any smells are instinctively repulsive I would imagine that feces would be high on the list.

Context is important to me. Manure in the right place is good. Manure in the wrong place is bad.

I used to work in a city 100km away from home - staying in a flat for the weekdays and driving home for the weekend.

Every time I drove hime, I would pass farmer's fields. The smell of manure on the fields became a goodbye from the grinding week of work, the welcome fresh outdoor countryside, and the harbinger of a well-earned weekend of leisure.

My wife doesn't like it, but for me, it smells like fresh air, countryside and freedom.

 

[jrmichler]

OK, since this thread has drifted way far away from lawn mowers

I simply love how you people can get a 50 message thread out of how starting a lawnmover works!

Time to start a new thread. Something like "Childhood STEM learning experiences that I somehow survived". This thread has clearly fully answered the OP, so is closed.