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Four-Stroke Engines Simply Illustrated: The Best Info-graphic We have Seen

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It’s sort of like admitting to your fraternity brothers that you are still a virgin.  Admitting that you don’t understand the basic workings of a four-stroke engine to your motorcycle brethren, can be embarrassing . . . but it is probably true for the majority of us.  Jacob O’Neal has created the following animated info-graphic that is by far the best, and most comprehensive explanation of basic four-stroke technology that I have ever seen.  It won’t teach you everything, of course, but for those who need a solid foundation in how a four-stroke engine works, it would be hard to beat the 10 minutes or so needed to study the following carefully.  If you click on the info graphic below, it will take you to a larger one on Jacob’s site.

How A Car Engine Works, by Jacob O'NealInfographic designed by Jacob O’Neal

25 Comments

  1. Haggis Eater says:

    Suck-Squeeze-Bang-Blow. Has that changed?

  2. NORKA says:

    I loved my old 2 stoke Yamahas. Flying down a back country 2 lane with the engine screaming; great fun. However, they went out of favor because by it nature a 2 stoke has a very limited efficient rpm range. Where a good 4 stroke can produce usable power from say 1500 rpm to 7000 rpm, a 2 stoke can produce a LOT of power between 5000 rpm and 7000 rpm, but little outside that range. The other major issue with 2 strokes is they burn their oil with the gas. Major pollution issue and you have to keep replacing the oil.

  3. Norm G. says:

    and now for a reminder of the development that changed the face of motorcycling in similar manner to what honda’s CB750 I4 did in ’69. seems like an appropriate thread…

    https://www.youtube.com/watch?v=oEXUrO5wYcE

  4. Gene says:

    Thanks, this will come in handy as I help teach my stepson to drive and harp on why he needs to understand what’s going on under the hood. Crappy first cars always last longer when you know what they need to keep running. Any chance you have a similar good site for clutch and transmission so I can show him why I go insane when he rides the clutch?

  5. Joe321 says:

    1. There’s no overlap in that animated valve timing.

    2. Stoich is generally considered 1:14.7, so wouldn’t it be more correct to round to 1:15? If your on the throttle, then the ECU will want something richer like 1:12.5, and highway cruise will lean out to around 1:17 for fuel savings. Saying 1:14 over simplifies things a bit.

    3. Injectors don’t always spray gas at a precisely timed moment, some fuel injected engines (usually older ones) use batch fire where they just fire once or twice per revolution. The diagram needs a cam rotation sensor if they want precisely timed injections.

    Overall, an interesting diagram though.

  6. chun says:

    the four stroke configuration seems like a lot of waste, cylinders having to go through their stroke twice. Why aren’t two strokes used in automobiles? And while we’re here, how do rotary and diesel engines work?

    • Norm G. says:

      Q: “Why aren’t two strokes used in automobiles?”

      A: survey says…!!! (*DING*) emissions. t’was the #1 answer.

      re: “And while we’re here, how do rotary and diesel engines work?”

      geometry, epitochroid cylinders. lastly, compression ignition.

      • chun says:

        emissions….aren’t two strokes being used in outboard motors still? the emissions has got to be stringent in that capacity as well, no?

        Epitochroid? that sounds like something you need a vaccine for. I’m going to lobby for economical 2-stroke auto engines that are cheap to buy, cheap to maintain and cheap to fix/replace. There must be a way…

        • Norm G. says:

          re: “aren’t two strokes being used in outboard motors still? the emissions has got to be stringent in that capacity as well, no?”

          yup, but the answer in the high volume world of on-road vehicles is still… emissions. doesn’t really matter what developments evinrude, orbital, and whoever have pioneered, the powers that be aren’t preoccupied with watching and regulating them. the feds target the “big fish” (pun intended).

          re: “I’m going to lobby for economical 2-stroke auto engines that are cheap to buy, cheap to maintain and cheap to fix/replace.”

          if your knees are up to it…? go ahead. (gary marshall voice)

          re: “There must be a way…”

          there is. what’s lacking is a will. unless you’re going to embrace 3rd world manufacturing and slave wagery (which has an inherently limited shelf life)…? “cheap” and “profit” make for strange bed fellows in the 21st century.

    • dino says:

      In a very simplistic view, there is too much overlap between intake and exhaust with most two strokes. That means too much unburned fuel going right out the exhaust. Not efficient with gas, and not clean for modern emissions regulations. 4-stroke engines go through the extra motion to completely separate the intake and exhaust, helping to optimize each step.

      However, some have come out with modern fixes to most, or all of these problems, but for some reason (cost, complexity, or just political reasons) these newer solutions just have not gone main stream.

      Old two strokes are fun, and generate a lot of power from an engine. I have an 1973 Kawasaki 350cc, triple cylinder two-stroke I used to ride years ago, and hope to get it back on the street after a couple decades in a barn!! Hopefully some of the newer 2-stroke designs can gain popularity!

    • Bud says:

      This video explains the rotary engine.

      http://www.youtube.com/watch?v=6BCgl2uumlI

    • NORKA says:

      I loved my old 2 stoke Yamahas. Flying down a back country 2 lane with the engine screaming; great fun. However, they went out of favor because by it nature a 2 stoke has a very limited efficient rpm range. Where a good 4 stroke can produce usable power from say 1500 rpm to 7000 rpm, a 2 stoke can produce a LOT of power between 5000 rpm and 7000 rpm, but little outside that range. The other major issue with 2 strokes is they burn their oil with the gas. Major pollution issue and you have to keep replacing the oil.

      • chun says:

        what about a 2 stroke makes its power so limited in the rpm range?

        • Jeremy in TX says:

          You can broaden, taper or move the powerband of a two-stroke as much as you like, just like a four-stroke. Ultimately, the engineers or tuners decide how much power they want and how that power should be delivered.

  7. Krisd says:

    Wow- the computer graphics make it really easy to see in 3D. Brilliant!

  8. Brinskee says:

    Wow, what a great reference. I’m going to use this the next time I have to explain the workings of the internal combustion engine. Well done!

  9. TF says:

    I learnt everything I needed to know by putting together one of those visible V8 engine models when I was about ten years old……that and a steady diet of roadrunner cartoons.

    • Dave Kent says:

      I had a similar experience, but it was totally different. I learnt everything I needed to know but “rebuilding” my clapped out trail 90 and only having half a coffee can full of small parts left over. It ran great , and I haven’t looked back since….

    • Tom Shields says:

      Same here!

  10. Erik S says:

    Distributor? What’s this a Model T engine :-)

    • Dirck Edge says:

      Distributors have been used in some modern engines, and it would not make sense to explain distributorless ignition systems in an introduction to how 4 strokes operate. In fact, the description is effectively accurate for both systems.

  11. Dave says:

    I wonder why the firing order is the way it is in the diagram (or in real engines). Seems like an uneven alternation.

    • Mike says:

      It has to do with crankshaft harmonics and vibration control. If they just fired down the line, you’d end up with some wicked vibrations and crankshaft motion unless you added some massive counterweights to the crank.

  12. nickst4 says:

    Are you really serious in saying that you think we-all don’t know squit about the oily bits?

    For shame!