Your tire is a little low on air, and you’d like to top it up back to the factory-recommended spec. You don’t grab out a traditional hand pump or electric air compressor, though. That would be silly. After all, isn’t your engine just a big old air pump? Why not fill your tires that way?
It might sound ludicrous and impractical, but it’s not as crazy as you might think. All you need is the right tool—an adapter that screws into a spark plug hole that uses your engine to shove air into a tire.
The spark plug tire pump is a beautiful piece of engineering, turning a simple task into an overcomplicated boondoggle. You get to dismantle parts of your engine, get filthy, and maybe even throw a check engine light, just to pump up your tires. Let’s explore how it works.
Four Strokes
The spark plug tire pump takes advantage of a simple property of standard four-stroke engines. They are just glorified air pumps, in a very simplistic sense. With the use of a simple adaptor, it’s possible to get your engine to pump air into a tire instead of just compressing it for later combustion.
The method of operation is simple. First, one must remove a spark plug from a given cylinder in the engine. It is replaced with the spark plug tire pump, which screws into the same hole. The engine is then cranked over to pump up the tire. On the intake stroke, the piston descends in the cylinder, sucking in clean outside air through a one-way intake valve in the spark plug adapter itself. On the following compression stroke, the piston rises in the cylinder, and pushes the air out through another one-way valve through the outlet tube and into the tire.
Thanks to the high compression of automobile engines, the spark plug tire pump could deliver plenty of pressure. As long as your piston rings weren’t shot, you could easily inflate a tire to 100 psi or beyond if so desired. Realistically, though, you’d be aiming for 40 psi or less for a typical automotive tire. As for the spark plug that you pulled out? You were best advised to leave it connected to the spark plug lead and leave it grounded against the engine.
It’s important to note that the spark plug tire pump is specifically designed to act as an air inlet for the cylinder. The device was designed very early in the automobile era, when the carburetor reigned supreme. If the spark plug tire pump merely relied on the engine’s existing air intake, the piston would suck in its usual mix of gasoline and air, before pumping it into the tire. Gasoline and rubber aren’t a great combination, so this behavior is not desirable.
By putting an air intake on the device itself, the piston primarily sucks in clean air from outside rather than drawing from the carburetor. It’s possible a small amount of flow might still come via the engine intake, but it would be reduced to almost nothing—as the tire pump was intended to operate at idle speed with the throttle closed.
It’s not clear precisely when the device was invented. As reported by Old Classic Car, various companies have built spark plug tire pumps over the years. Schrader made some of the most well-known versions, dating back to at least 1948 based on an advert from Popular Science, seen below. If that name sounds familiar, it should. The company was founded by August Schrader, who invented the Schrader valve used in the majority of automotive tires today.
Schrader’s spark plug tire pumps were typically shipped with a few accessories for ease of use, including a variety of adapters for fitting the pump to engines with different spark plug threads. A pressure gauge was also commonly included on the air hose so one could monitor the pressure of the tire being inflated.
There is earlier evidence of similar devices, too. Advertisements were placed in a publication called The Autocar in 1919, reporting on devices called The Pioneer and The Engo-Flator. The former is listed for “all types of cars” while the latter is intended “for small and light cars.” The Engo-Flator appears to work in the same manner as the Schrader device, highlighting that it delivers “pure air” into the tire. It retailed at a price of “39/6″—39 shillings and 6 pence—a pre-decimal price so complicated I won’t even try and translate it into today’s dollars.
Weirdly, the Pioneer is advertised somewhat differently, with the ad claiming “it is the one Spark Plug Pump which does not deliver air to the tyre through the engine cylinder—an absolute guarantee of purity.” The ad also claims the Pioneer can inflate “any size of tyre to full pressure, irrespective of engine compression.” It’s unclear how it may differ in construction from the Engo-Flator, but both were produced by Fluid Pressure Pumps, Ltd. of Latimer Road, London. In any case, the Pioneer retailed for a far higher price of 3-and-a-half guineas, because British currency was an absolute joke in 1919. With a guinea equal to 21 shillings in the early 20th century, the Pioneer cost roughly 73 shillings and 6 pence, if I’ve got the math right.
We can Vintage examples of these tools are readily available via online auction sites. Beyond the many Schrader listings, you can also find examples from companies like Milton and Imperial.
You can actually still buy newly-built versions too. Prism Supply Co. sells the Kick-N-Fill Air Pump, intended for use specifically with Harley Davidson motorcycles. It’s unclear, however whether this version has a clean air port or if it just uses engine intake air to fill the tire.
Remember how we mentioned carburetors earlier? That’s important. Specifically because you wouldn’t want to use such a device on a modern fuel-injected engine—for a multitude of reasons!
In a classic vehicle using a carburetor, if there is very little flow through the engine’s intake port, little to no fuel will be sucked through the carburetor’s venturis and into the cylinder. This is because the fuel dose is directly related to the airflow. However, on a fuel-injected engine, the injectors will squirt fuel whenever commanded by the engine control unit—whether or not there’s much airflow going into the cylinder at all. In a throttle-body or port-injected engine, some of the injected fuel would likely trickle past the intake valve. The rest might end up creating a rich mixture condition in the intake and get sucked into other cylinders. In a direct-injected engine, it would go straight into the cylinder, and then get pumped straight out into your tire. That’s bad. You don’t want that to happen.
There are other issues, too. Your modern fuel-injected car does not like running with a spark plug disconnected. The engine will detect the missed combustion event and probably throw a misfire code, triggering a check engine light. A modern ECU is not programmed to deal with weird situations like hooking up an air pump to one cylinder, and it will throw a fit until you put things back the way they should be. To say nothing of how difficult it can be to access spark plugs on some modern engines.
A well-preserved example of the Schrader pump.
Even on simple older engines, the use of these devices was non-ideal. Overspeed your engine or pump too long, and you could easily overinflate a tire. You also had to muck about pulling a spark plug just to inflate your tire—an oily task, if an easier one on older cars.
Really, though, these devices have disappeared for one major reason: There are far simpler ways to pump up a tire. You can pack a simple hand pump, which is slow but workable, or you can carry a battery-powered pump instead. Virtually every car has a 12-volt power socket, too, which can easily run a small pump or compressor for this exact scenario. None of these solutions require disassembling parts of the engine or getting greasy just to fill a tire.
It’s possible to see some value in obscure situations. For example, the Prism Supply Co. tool is very simple and very lightweight. It might make sense when roadtripping a vintage motorcycle. Even the lightest battery-powered pump would likely be more ungainly and less reliable. But in the vast majority of cases, a modern electric pump is a far cleaner and more versatile solution.
One might think of the spark plug tire pump as a product of a less complex time, when we were ultimately closer to the mechanical truth of the machines that hauled us around. Today, we live on top of layer upon layer of abstraction, where even a simple tire pump has batteries and screens and buttons and so many more things to go wrong. Still, the complexities of modern life afford us so many conveniences, such as not having to dig around under the hood of our cars when we need to pump some air in a tire. Perhaps it really is better this way.
Image credits: Schrader, Amazon, Fluid Mechanics Pty Ltd., Prism Supply Co., ScoutCrafter via YouTube screenshot
These things worked well enough back in the day before 12 volt compressors to save considerable time over the hand or foot pump. Once those noisy rattlecan 12 volt pumps came around though, these tools were consigned to the backup box cause the extra faff of dealing with a spark plug and the tools required was totally cut out by just two alligator clips on the battery.
Umm, just carry a hand/foot pump! (or an electric one if you live in this century…)
You spare all the time fiddling with a spark plug and don’t risk messing up any thread or losing parts or not putting everything properly back together, but the actual filling the tyre might take a bit longer…
–Also works on diesel cars! 😀
Yeah, but how do I fill my tires w/ exhaust smoke? Or can I also use the Lucas Electrics replacement smoke? Also, just a reminder to switch over the winter air in your tires to summer air
Back in the last century plenty of motorcyclists carried these in their saddlebags. I only had to use one once, but it worked. Thank goodness for the electric compressors though. Most bikes had a handy spark plug hanging out in plain view then.
It’s not much help for the V-twin and thumper crowd. I doubt you could get most old cruiser motorcycles to start on a single cylinder, considering how hard they can be to start with two. Dirt bikes and the smaller displacement Hondas I usually rode only had a single cylinder.
I remember those. I’ve only ever seen them used on tractors though. I had an aunt that had one for her corvair I’m not sure she ever used it but her husband had given it to her because they used something similar in the military.
I remember seeing these ages ago. But I never had the opportunity to use one. In my old jeep I used a hand pump or a foot pump and set aside an hour to air back up in the desert. 15 minutes per tire with a rest break. I always wanted to convert a York a/c compressor to use as an air pump but never got around to it.
It’s interesting that this exits/has existed, but frankly, I’d much rather stick a plug into the 12V socket in the dash (what old guys used to refer to as the ‘cigarette lighter’ for some reason) for a Harbor Freight compressor to fill a tire rather than keep a deep 13mm socket and ratchet in the car and go to the trouble of pulling a spark plug just to top off a tire.
I’m sure someone will disagree, and that’s fine of course.
Also, some post offices in Canada apparently have small ‘fitting rooms’ where people can try on clothes they just received from online purchases… if it doesn’t fit, you’re already at the post office and can send it back immediately w/o making a second/separate trip.
Of course, this assumes you’re carrying a smartphone (to get the return going) and aren’t nervous about standing in a closest in a post office in your undies. And that you didn’t get this clothing item delivered to your own house for some reason (I know, some folks prefer/have PO boxes, etc…). But assuming all those conditions are covered, having a dressing room AT the local post office where you can try on those dark olive green insulated overalls you ordered last week when you had that second glass of wine, seems like a great idea.
Unless Youtube lied to me about this… but I saw like three different post offices as examples in meme montages. Plus, I’d like to believe that it’s true. So there. 😛
We used one of these all the time in the early 1970s as we roamed off-track through California’s deserts. The car was a VW Thing, we all knew how to take out a spark plug, and tires we aired down to 15PSI or so went right back up to 30PSI with the inflator. No problems at all!
Used one of these on the farm. Worked great. John Deere 720 with 38-14 rear tires and a slow leak, the 5 gallon air tank on the pickup wasn’t quite enough. Then we started filling the tires with water, with just a little air for softness. Usually didn’t leak much after that.
Of course we put it on the pickup’s engine , not the tractor’s. 180 cubic inches per cylinder would have made it interesting though. Probably wouldn’t run on only one cylinder come to think of it. Now I’m curious. Anyone know if a John Deere will run on one cylinder? It does have that manhole cover size flywheel.
As someone who had to do this once, I can say it works in emergencies but I do not recommend it. Not only is it slow, but it’s also exhausting. I put about 10 PSI in my relatively low volume Prius tires and I was pretty much toast by the time I was done. If it had been a big truck tire or I’d had to reinflate it from flat I’m not sure I physically could have.
I guess that’s the one argument in favor of low profile, rubber band tires. They probably don’t have much more air volume than a bike tire so you can pump them up quickly, even by hand. 😉
I now carry an 18V Ryobi inflator in all of my vehicles. It’s a bit larger than the integrated ones, but periodically I can just swap the batteries so I don’t have to worry about pulling it out in an emergency and finding that the battery is dead because I forgot to charge it (or remembered to charge it but forgot to put it back in the car). I also don’t have to worry about the cheap battery dying and leaving me with a worthless brick.
The hand pumps for car tires with a 3 inch bore are quick and easy, the 3/4 inch pumps for 100psi bike tires will take all day.
Umm. A smallish hand pump works great for me for tires that size (on 1996 and 2003 Legacys, 2010 Prius formerly). If just topping off a tire that’s a bit low, my small (1-inch bore, 11-in stroke) plastic bike floor pump that I keep under the trunk floor of the car takes just 20 seconds or so before I stop and bleed out the excess. If it were 10 psi down, I’d probably pump for about 45 seconds before checking where it was. I am admittedly an athlete and don’t mind using physical effort. When my newer (2003) Legacy was still running old tires from the previous owner, one of the tires had a leak that progressively got worse (while waiting for a tire on order) until I was pumping it from rim on the ground every day. That 205/55-16 tire still only took 4 minutes (admittedly vigorous) effort from zero using that small pump. With a real full-size bicycle floor pump, it would have been 2x faster.
Maybe my pump just really sucked, but it took me at least 10 minutes of pumping like crazy to get my tire back to where it was relatively safe to drive home on.
This immediately makes me think of the amount of unburnt fuel scrubbing the oil from the cylinders and going into the exhaust. Sketch.
Quick Q, can I jump start the engine with my tire?
You’d have to at least figure out what cylinder was in the right position just after TDC to push down on, but sounds like an interesting science project. Probably best done with a modern DI engine so you could quickly fire the engine in the first 1/2 crank revolution, similar to some research from some years back looking at if DI could enable starting an engine without a starter.
The really fun game though would be the whack a mole variation of trying to reinstall the spark plug in the running engine, I would watch that youtube video if it existed, especially if there were combustion flames shooting out the hole every other engine revolution anytime the spark plug got close
There is (or was) a related system for aircraft engines – a blank rifle or shotgun cartridge. It would give the engine enough of a kick to get turning over, and hopefully start.
Flight of the Phoenix ftw.
Used on tractors as well.
Ha, yeah, maybe if your car is a pre-WWI Pierce Arrow, S.C.A.T., or Wolseley. Some of those cars, before the advent of electric self-starters, used compressed air systems, with tanks of air (ha, a tire is basically a tank of air after all) for starting their engines. Not altogether easy to find information on pneumatic starters used in such cars online; more information is out there for agricultural/industrial applications such as tractors and construction/factory equipment, though. If you all ever write up such an article I daresay there’ll be quite a few of us interested in reading it. Did find a very few posts online such as this: http://www.mtfca.com/discus/messages/411944/418429.html?1390700092
No, we have to dig through the innumerable menus in the touch screen to accomplish anything, valuable or not. BC everyone follows Elon.
It is not better this way.
No, it’s much much worse.
Or is it?
Yes, it is far worse.
I assume this is the same Schrader that invented the Shrader valve, used for filling up tires? That’s kind of cool.
That is correct- August Schrader, founder of A. Schrader’s Son Inc, which is apparently still in business as a manufacturer of diving equipment in Ottsville, Pennsylvania
Makes me want to own a gas station only so I can park a junk car in the corner, hook up this rig, and have a sign “Free Air, just start engine”
With an old flathead or early OHV engine this makes perfect sense.
Never seen this one, but I used one on travels in Mexico & Central American for my Honda SL350 in the Seventies. It worked fine!
A riding buddy had one, that was early 90s?
These days I can walk to a tire shop faster than I could find and remove a spark plug from a modern engine.
And maintain whatever remains of your dignity.
My shop teacher in high school had a vw engine that had 2 cylinders modified to be air compressors and the other were stock. I think he pulled the lifters out on the 2 that were compressors and had check valves like this. He had a little generator run to the output shaft too. It was a cool little tool
If I was using this on an analog car, I’d disconnect the distributor from the coil, that way the engine won’t start up on you.
We used to do this when doing an oil change on a turbo, in order to get oil to the turbo before actually firing up the engine.
I’ve got a 1940’s military version of this for my 1945 Willys MB army jeep. I’ve never been desperate enough to try using it.
Now there’s an application this device is perfect for. Stuck out in a French forest with a flat tire and Jerry on your tail.
Lewis, Springer or Seinfeld?
elon
It was a World War 2 reference.
It’s clever, and you could do this on a fuel injected vehicle, you would just have to disable the injectors too. This would be a good little kit for an ADV bike. Especially a small single cylinder one.
Yeah, I could see this being a decent emergency tool for a bike or something else that might get stuck away from civilization. A part of me wants to find one just to see if my recently revived Vespa could pump up its own tires.
Would be great for a Moto Guzzi.