Small Engine Pondering

[pyat]

So, do gas push mowers have a battery, to provide spark? Mine has a key ignition, suggesting that there is a battery somewhere, surely? The ley ignition does nothing, and never has, so long as I've owned the beast - it's second hand. The pull cord worked in past years, but I could not start it today. After inspecting the spark plug, checking the gas and oil, etc., I can find no reason for it's reluctance.

Why is this keeping me awake? I have to be on a bus in 7 hours.

Also, the rusting tool that's been hanging in my garage since I moved in, left by the previous tenant? Swivel-head spark plug wrench. I'm going to write about that tomorrow.

Comments

[zorinlynx.livejournal.com]

Small gas engines don't use batteries; they use a magneto:

http://en.wikipedia.org/wiki/Ignition_system#Magneto_systems

It's a simple and reliable system for generating electricity for the spark.

The switch to kill the engine basically interrupts this circuit so there's no spark. Another way to kill a gas engine is to ground the spark plug to the frame, but this can be less reliable than just opening the circuit. And yeah, with a lawnmower you want it to stop immediately when you tell it to! :)

[pyat.livejournal.com]

I figured they would not have a battery, normally.

However, the switch is an ignition key - like, to turn it on. According to the manual, the pullcord just a backup. Since there's no muscle power going to turn the dynamo, I assume there must be a battery involved somewhere.

[firesign10.livejournal.com]

If you are using the ignition, it would use the battery. If you are using the pullcord, it's falling back to the purely physical magneto thing and the battery is not involved or an issue.

[pyat.livejournal.com]

Hmm. Yeah, that makes sense. And, as I noted, the key has never worked, so presumably the battery has always been dead, and it never interfered with starting before..

[archai.livejournal.com]

Mmmmeh. Yes and no. If there's an ignition with a start position on it, it has a battery and a motor/generator permanently geared to the crankshaft (and if the start position doesn't work, one of these, likely the battery, has failed).

When you turn the key to start, it juices the motor, which starts the engine, which then keeps spinning the motor/generator as a generator to recharge the battery from starting the engine. At no point is the battery ever providing spark, though.

Briggs and Stratton engines use a ridiculously simple version of the magneto - there's a huge magnet in the flywheel, and it fires every time it comes past a set of inductor coils bolted onto the block. That's it. They never, EVER break, and neither do they need battery assistance. The ignition switch simply shorts the spark to the block to shut down the motor, which coincidentally you can also do manually with a wrench, screwdriver, or pocket knife to get the same effect in an emergency. Just don't touch anything to the spark plug FIRST, and be ready for a bit of a jolt if you get it wrong.

Wait...

[pxtl.livejournal.com]

Hold on, there's actually a device called a magneto?

Next you'll be telling me that there's an animal called a wolverine, and a mythical beast called a cyclops.

Re: Wait...

[pyat.livejournal.com]

Scott Summers has TWO eyes!!

[firesign10.livejournal.com]

Advice from my Blogula:

Two things to check out of the gate:

1) clean the air filter - it is really easy to have that be too clogged to provide air.

2) remove the spark plug and test it - it might LOOK ok but still not generate a spark. Safety is an issue here - he said to look online for a how-to on testing spark plus (it was more than I could type here...). If this is second-hand and you have never replaced the spark plug, just go ahead and get a new one.

Also, check online for an owner's manual. Even older machines now have their manuals online a lot, and that may have more specific instructions.

Hope something here helps! :-)

[pyat.livejournal.com]

I checked the air filter last night as part of my poking around at it, and it seems fine. Fairly clean, even, since I have a tiny lawn.

Spark plug is the next step!

[anidada.livejournal.com]

You can turn it in for a credit toward a nice shiny, environmentally friendly reel mower, if you can't fix it... Try Home Depot, Canadian Tire, probably Rona and Loews.

Or replace your grass with something that doesn't need mowing. :)

[catsarah.livejournal.com]

Also...Lee Valley has nice reel mowers.

[pyat.livejournal.com]

It's a very good mower - indeed, too good for a lawn my size. I acquired it from Cats' late stepdad, and it was designed for a much larger property. It's fairly new, too. I'd be more likely to sell it, and use some of the proceeds for a reel mower.

[warphammer.livejournal.com]

Or what my dad did for his tiny yard: Electric.

[pyat.livejournal.com]

I was raised on electric. Sigh. So many chopped extension cords. :)

Maybe a battery one, though.

[warphammer.livejournal.com]

Yes, the battery type. That's what he uses.