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evilleppy87 t1_iwdrhoe wrote

Is it just me, or is the exhaust timing wrong?


Inle-rah t1_iwehpwm wrote

First thing I thought - I totally wanna lobe that cam. It’s gonna “pop” when the intake opens. Love the animation and rendering though.


ClassBShareHolder t1_iwfgub4 wrote

Not animation. It’s a polycarbonate model. I too thought it was animation until I looked closer at the cylinders and connecting rods.


Inle-rah t1_iwfhaeo wrote

Holy guacamole! That’s awesome!


bentsea t1_iwfim5p wrote

It would be if the timing were right. As it is, it's just a physical trigger for deep psychological trauma.


guerroconpollo t1_iwdvhhq wrote

Definitely not wrong. It's like it's missing a beat in a dance.


yodazer t1_iwgbtv8 wrote

It is very wrong. It looks like they are sucking in the exhaust instead of pushing it out.


MarcoMontana t1_iwgjusc wrote

The cam is not timed at all, this engine if it started would rumble an pop all over the place.


cbxsix t1_iwg5had wrote

It's off because of the huge amount of lash. The valves open too late and close too early because only the ~top half of the cam is actually hitting the valve stem. Otherwise it's a cool model!


Wayed96 t1_iwgc821 wrote

All the timing is wrong. But it gives the general idea I guess


shifty_coder t1_iwgob0g wrote

Isn’t the ignition order wrong, too? Would a three cylinder fire sequentially, or wouldn’t it fire 1-3-2 or something


Elkazan t1_iwh07to wrote

1-3-2 is the same as 3-2-1 which is also sequential, just in the other way. Would it change anything? Seems pretty equivalent to me.

Disclaimer: I don't know about engines.


shifty_coder t1_iwh0owc wrote

That makes sense. It doesn’t matter what the crank order is, the ignition order will be sequential.






ct_rugen t1_iwfdnrn wrote

You're telling me you see that but you haven't been 180 off on a cam or distributor timing. I know Ive missed a timing belt or chain a few tooths off a lot of times


allwaysnice t1_iwfs3bi wrote

I know nothing other than 20 years ago when I watched this on Magic School Bus and it still felt wrong.


Aggrador t1_iwghsgt wrote

Doesn’t look wrong to me. Red exhaust valve opens as the piston rises and blue opens when the piston drops on each of the cylinders. I will say though, that this does look like an awfully unbalanced engine between cylinders 1 and 3 having so much time between the firing orders, as oppose to 1 to 2 or 2 to 3.


johnnySix t1_iwgj3j7 wrote

It also looks like the middle gear is going the opposite direction of the arrow and handle.


drsbd t1_iwdsbdp wrote

I think it's just you but don't quote me on that


evilleppy87 t1_iwdssjt wrote

Shouldn't it be open til the piston reaches TDC? If so that means with those cams it should open later in the exhaust stroke. It seems like they start opening just before the piston reaches BDC, and close half way up the exhaust stroke.


drsbd t1_iwdur3t wrote

Now that I look again you're right they are only open for roughly half the exhaust stroke. Good eye


Waldron1943 t1_iwerj2m wrote

They do open before BDC. Imagine a graph with two curves plotted. One curve is the "benefit" you get from leaving the valve closed and using every last bit of pressure. The other curve is the "benefit" you get from opening the valve early and starting exhaust flow. Those two graphs cross before BDC; there's more "benefit" to opening the valve than there is to keeping it closed.

Also, it's actually open past TDC. Right at TDC you've invested energy in establishing flow; if you slam the exhaust valve right then that flow just "piles up" against the valve, which doesn't help you. As a matter of fact, the intake valve opens (and stays open a surprisingly long time) before the exhaust valve closes...that's called "valve overlap". Less overlap = low RPM power, longer overlap = high RPM power. Overlap uses that flow through the exhaust valve to pull more fuel & air mixture into the cylinder.

Valve Overlap


myawesomeself t1_iwgmva8 wrote

I think this is what everyone expects, that the exhaust should be open near TDC so it might overlap with intake a little, however in the model it clearly closes completely somewhere around halfway up and there is a noticeable gap between the exhaust valve closing and intake opening which is the unusual timing people are talking about.


Waldron1943 t1_iwhkl0j wrote

Oh yeah, I mean in real engines. The model is all fuxored up; check out the valve clearances!


Snufflepuffster t1_iwe3wrq wrote

often valves close or open early to take advantage of acoustics (shock waves) to ram air into the cylinder or throw it out. So timing is very nuanced and can be adjusted drastically from engine to engine. In general the exhaust valve isn’t going to match the stroke, it might be early or late, extended or short due to design.


evilleppy87 t1_iwe8c32 wrote

I'm aware that there's going to be some variability, it just seemed to me that closing 90° before TDC was a little extreme, especially considering in most cases the exhaust valve closes a little after TDC


Drunken-samurai t1_iwge1ej wrote

Bringing up variability, there is VVT (variable valve timing) which takes advantage of this in real time to use different valve timings at different RPM's to provide more efficiency or power.


evilleppy87 t1_iwgrf7o wrote

Like Honda VTEC, for example?


Drunken-samurai t1_iwkt2fq wrote

Yes your right, this is part of what the VTEC acronym is (Variable Valve Timing & Lift Electronic Control).


Wayed96 t1_iwgmkik wrote

And even a little longer to improve intake speed


mkillham t1_iwewndf wrote

I still have no damn idea


TheRealASP t1_iwftvhu wrote

3 boom make car go. 3 more boom make car go more!


OrionHasMemes t1_iwf2sqi wrote

I agree it looks a little confusing.


Wayed96 t1_iwgccsk wrote

Doesn't look confusing at all. There's just no explanation attached so that might make it confusing


Koreanjesus4545 t1_iwhpa3u wrote

So you're saying for someone who isn't knowledgeable on the subject, it's confusing?


johnson_united t1_iwg5bhs wrote

Intake - piston travels down to pull in air/fuel mix; compression - piston travels up to compress mix; power - mixture ignites, forcing piston down; exhaust - piston travels up to force out exhaust; process starts over.

Exhaust cycle for the valve timing seems a little bit off, but it’s close.


bill_gannon t1_iwg6jix wrote

Lol it's way off.


johnson_united t1_iwgbhre wrote

You’re right, I slowed it down. Exhaust is opening at BDC, usually it’s cycle is 100-5 degrees BTDC.


Aggrador t1_iwgil6q wrote

It is just a diagram after all, not a precision-built machine, so I don’t think we can expect much in terms of ultra-realism. There are other things wrong with it, too, like no valve overlap, and the firing order has a noticeable lag between cylinders 1 and 3, makes for a very unbalanced engine.


illBro t1_iwgqbup wrote

It would be easier to make it correct in a diagram vs real life.


Aggrador t1_iwgso6i wrote

It would be easier, but it’s not super critical either. This gives you a general idea of how a 4-cycle engine works. All I was trying to say is you could pick it apart and find everything wrong with it, but at the end of the day, it is just a diagram. But yeah, i agree, it would be easier to make in a diagram vs real life.


zebrawithnostripes t1_iwg5co5 wrote

Blue valve opens, gas gets injected, piston is pushed back up, gas compresses, spark, boom. Red valve opens and smoke exists. Note how the piston does 4 up/downs in a cycle. Only 1 of those steps is powered by gas dirextly. The 3 other steps are powered by the movement of another piston.

The real beauty in there is the cam shaft IMO. The green things moving the valve. They have to be perfectly configured andnthe gear ration needs to be precise otherwise the valve wouldn't open at the right time.

This is not my expertise though ... I could be wrong


Wayed96 t1_iwgckmt wrote

>Blue valve opens, gas gets injected, piston is pushed back up, gas compresses, spark, boom

"Gas" is not injected. Air is sucked in because the piston moves down. Fuel could be injected either directly or just before the blue valve.


danivus t1_iwg835k wrote

Explosion makes piston thingy move, which turns other thingy and makes wheels turn.


g2g079 t1_iwdpq42 wrote


Chapman79 t1_iwe8m7y wrote

Thank you, I think this is the coolest thing I’ve ever seen in my whole life. I LOVE those gifs and the explanations are fantastic.


g2g079 t1_iwedb7c wrote

Glad you enjoyed. It's one of my favorites.


polyic t1_iwey3jn wrote

Oh my gosh! I’m so happy to see this site is still around. I remember using this to learn about engines when I was little. Thank you for sharing!


CaPtian_CaTe t1_iwfj2tl wrote

Do you have any other similar websites which explain things related to automobiles or aerospace?


spiderborland t1_iwh5y2v wrote

Looking at all of these I'm happy to know that computer precision and magnets are replacing our traditional engines. We've gotten really good at squeezing every bit of efficiency out of internal combustion, but it's wild to me that, as someone else said, "boom make car go." Controlled explosions feels very archaic for how much effort we put into driving.


Aquamarooned t1_iwhheca wrote

Look up how an impact drill works.. in slow motion its literally teeth slamming into eachother to spin the motion and its not as smooth tolerance as it would seem when you play it normal speed


J_Megadeth_J t1_iwe1zr7 wrote

This is definitely inaccurate with the fuel injection and exhaust.


Skeetronic t1_iwfe5vv wrote

What part is the exhaust?


bigbaltic t1_iwfhnov wrote

Red is exhaust, blue is injection.

Blue opens to inject, piston draws in Piston compress Light (spark) ignites Piston expands from explosion Piston compresses exhaust Red Exhaust valve opens Piston expands because moment Piston compresses Repeat

The exhaust looks early but I am not familiar enough with the mechanics of engines to say definitely.


J_Megadeth_J t1_iwffat2 wrote

I think red is fuel injection so blue is exhaust. It should be opening when the piston compresses the second time.


IdleFool t1_iwfrcbb wrote

Red is exhaust blue is air intake. Idk about fuel injector though I don't see it


GustavSpanjor t1_iwfm9is wrote

Exhaust should be open on an upstroke so that the exhausts get pushed out. Now both exhaust and fuel intake is open on a downstroke.


shikuto t1_iwfsmbv wrote

>Now both exhaust and fuel intake is open on a downstroke.

No they’re not… Watch it again. Blue (intake) is open on a down stroke, red (exhaust) is open on the up stroke.


Baby_Rhino t1_iwg9jin wrote

Sorry to be pedantic, but injection is the wrong term here. We can see the fuel/air intake in this gif, but fuel injection is not shown.


TheSpatulaOfLove t1_iwdrxod wrote

Suck squeeze bang blow


guerroconpollo t1_iwdok29 wrote

How a four stroke engine works.

A thing of beauty.


DekaFate t1_iwepi1c wrote

So what happens when you “ throw a rod “


CBus660R t1_iweyara wrote

The bottom green part breaks. The top green part is the camshaft. The yellow part is the crank. The orange is the piston.


Rhodog1234 t1_iwfajx8 wrote

This can easily be accomplished by driving a 1978 Trans am 6.6 with a 400 big block at about 68 mph and quickly downshifting ( without sufficiently pre braking )... Still brings a tear to the eye


Dynasuarez-Wrecks t1_iwf6pnz wrote

"Throwing a rod" means that a connecting rod breaks. In this example, the connecting rods are the three green pieces near the bottom connecting the crankshaft (the yellow part) to the pistons (the three orange parts). Everything is moving very slowly here, but in an actual engine, connecting rods can be moving with enough energy to eject them completely through the crankcase (the engine's body), hence the term "throwing."


YouCanFucough t1_iwfuamo wrote

The green parts at the bottom are the crank-rods. If the crankrod bears too much torque from the crankshaft (yellow) it can break.


witzed1 t1_iwgmy47 wrote

The part, the connecting rod, connecting the piston to the crankshaft breaks. Usually due to some catastrophic problem like overheating or oil starvation. Something has prevented normal piston travel.


keuzkeuz t1_iwebfyx wrote

The ole 1-2-3 firing order. I'm more fond of the 2-3-1 myself.


Gordath t1_iwfj9mu wrote

It seems like the exhaust valve is closing a bit too soon?


alx924 t1_iwf5dl6 wrote

Looks like a Geo


Rhodog1234 t1_iwfa3eo wrote

I had a 92 Geo Storm ( so I actually had 4 cylinders 😜).

I Absolutely LOVED that car. Got it right after a desert deployment, and after the rebates and military factory incentives , I got it for @ $6,000 . It would do 120 mph [source: was pulled over by Kansas state patrol officer who had a stopwatch showing exactly 30 seconds, and he told me that was my last mile. Was standing at parade rest the entire time and the good ol boy let me go with a warning! Whew] It would get as many as 48 mpg ! ( When driving considerably under 120) And the stereo with installed 12 band graphic equalizer w booster and detachable woofer box in the back ROCKED ! Ended up selling it for $4,800 4½ years later when I went to Korea.

Sorry... Little trip down memory lane... But yeah, the other Geo model had a 3 cylinder motor 🙂


RJR79mp t1_iwfbeco wrote

I had a Geo Tracker. It had the aerodynamics of a barn door but.... I seriously got 38mph, went 88mph with 5 adults, always started and 141,000 miles.


Rhodog1234 t1_iwfbid4 wrote

Yess, Tracker. Thank you, I couldn't remember the name haha

Edit I just remembered the Metro... That was the 3 cylinder model I believe


alx924 t1_iwfcnyu wrote

The Storm was like half of a Camaro. I checked the curb weight of the two. The Geo was 67% the weight of the Camaro. So I checked the power. Depending on specs, the Geo was 57-67% as powerful as the Camaro. So I’m really not surprised you could get that thing moving so fast. The Camaro has a slightly better power to weight ratio, but only by 3lb/hp.


Rhodog1234 t1_iwfdevs wrote

Exactly! So many didn't realize how sporty and performative it was ... Plus it had the flip-up headlights which were cool af Imo


alx924 t1_iwfgt32 wrote

I had a 1992 Ford Probe with the 3.0 Liter V6 that my cousin gave me for free when my Jeep died. I drove that thing for 5 years with very few issues. It had the flip up headlights as well. I loved that car. I only sold it because I was moving out of state. My sister lived there another 4 years and she still saw it driving around. It was otter-pop blue, which was hard to miss. I remember beating mustangs off the line at stop lights from time to time. It was a fun car.


Rhodog1234 t1_iwfhfvn wrote

Nice .. totally forgot about those. Tbh I wasn't much of a Ford fan back in the day, but my cousin ( whose father had been a Ford plant employee so he got discounts ) had several different models over the years .


Riegel_Haribo t1_iwfl47l wrote

2014+ Ford 1.0L ecoboost also is a three-cylinder engine with direct-acting bucket camshaft. It, however, is dual-overhead-cam, and quite unusual in having a oiled timing belt, oil-powered variable valve timing, belt-driven oil pump, and over 200% the power output of a Geo.

Here's a video with multiple angles of internal engine operation:


hellcat_uk t1_iwfpbp7 wrote

Looks a lot like the Fiat TwinAir with the integrated exhaust manifold in the block and the oil powered variable valve timing though I can't see if the timing is individually controlled. Extra cylinder in the Ford obviously!


Mr_Ted_Stickle t1_iwfbswn wrote

Slap this bad boy in a civic and you’re good to go. Add a piston and a cam if you’re feeling frisky.


devnull1232 t1_iwfe7gi wrote

Are valves still mechanically controlled by an overhead cam or are they run by the ECU these days.


[deleted] t1_iwdomc0 wrote



devnull1232 t1_iwfekmb wrote

I mean, take off the exhaust manifold and have yourself a peak at them. While the engine is redlining.


zomboromcom t1_iwdpa7q wrote

Don't put your dick in that I'm not the boss of you.


mrgenier t1_iweaemi wrote

Introduced today the combustion engine would never make it, advanced yet so primitive


Flagil_Reinhumps t1_iwf5n72 wrote

This is so amazingly complicated I feel like electric motors will make us dummer.


witzed1 t1_iwgnw59 wrote

There certainly will be less work for mechanics.


Away_Brilliant_4660 t1_iwf69c7 wrote

Oh yes i see now. How could I have not understood before?


Wallace_W_Whitfield t1_iwfbadf wrote

I’m a little confused. I know nothing of engines, but those lights look like they are not synced up


shikuto t1_iwfsfkn wrote

The lights (combustion of the fuel) happen at the top of every other movement of each piston. If you watch just the left-most piston, you’ll see the 4-stroke cycle (aka Otto/Diesel cycle, aka suck-squeeze-bang-blow.)

If you start watching the first piston right as the light flashes, the piston is at the top of the stroke length. This is the combustion portion of the cycle, or the “bang” part. This combustion creates rapidly expanding gas, pushing the piston down the cylinder.

Once it gets to the bottom of its travel, you’ll notice one of the valves at the top of the cylinder open up. Then the piston rises back up the length of the cylinder. This is pushing the exhaust gas out of the cylinder - the “blow” part.

After that, the exhaust valve closes, and the intake valve opens up. The piston is traveling back down the cylinder, due to the other pistons rotating the crankshaft. This pulls in air, and at the same time, modern internal combustion engines will spray the fuel of choice into the cylinder via fuel injectors. This is the “suck” part of the cycle.

Next up, at the bottom of the travel again, the intake valve closes. The piston travels back up the cylinder. Since it is now a sealed environment, the air-fuel mixture inside is compressed. This is the “squeeze” part. Then we’re back to the “bang” when the light goes off again.

In a diesel engine, the pressure and temperature alone cause the fuel to ignite, while gasoline engines utilize a spark plug for ignition. Ignition from pressure and temperature alone in a gasoline engine is referred to as detonation, and is a particularly bad thing to have happen.

It’s a little unorthodox to start the explanation of the power cycle at the ignition phase, but I think it’s useful to have the light as a good starting point when there’s a visual representation.

Hope this cleared something up for you!


drjude518 t1_iwfo0e0 wrote

Very beautiful. Whether it works or not I want one. Are those emeralds at the top? Could do the whole thing again made out of precious metals; gold, argentium, platinum….


TSMC_YT t1_iwfiu6i wrote

Well this explains everything


weewillywinkee t1_iwflf7b wrote

Did work experience at a Shell research centre back in the 90s, they had managed to produce a crystal piston chamber for watching the combustion process after many attempts and failed prototypes. Not thought about that for years!


gazette1895ky t1_iwflnf9 wrote

I was studying about this and discovered that gears do functions similar to levers, it is really amazing how one force acts on the other.


wert1234576 t1_iwfmkhz wrote

Okay but where does the little wizard live?


SupineFeline t1_iwfoqmd wrote

Well that explains it so clearly!


SassyMoron t1_iwfwcxu wrote

It's an air pump, really. Locomotion is just a byproduct.


Wuntoothrie t1_iwgeesg wrote

Sort of. What this doesn't show is the synchronized explosions that force those pistons down. That little flash of light is the spark that ignites the gasses (air and gasoline, in many cases). The explosion is contained in the cylinder and pushes the piston and the arm down rotating the cam shaft.


SassyMoron t1_iwh0r46 wrote

I think the yellow lights are supposed to symbolize that


Wuntoothrie t1_iwh2oa7 wrote

Pretty sure that's just the spark plugs, but it would be nearly simultaneous. So you could probably pretend that it somehow is the same thing and fool the not so bright kids into learning something.


Mayberley t1_iwfz58h wrote

Yeah. That is not showing me how it works.


bbiggar500 t1_iwg5rt0 wrote

Way too much valve lash. Please adjust those.


Nerdler17 t1_iwg6dqj wrote

This is why electric motors are so much more efficient.


skylorddragon t1_iwg8xsg wrote

Can someone do this and explain 'gears' to me? 1st gear, second, third gear. Speed wise.


cptstupendous t1_iwga5py wrote

At some point in the future, intimate knowledge about how these engines work will become as scarce as the knowledge of old programming languages like FORTRAN and COBOL.


therandomopera t1_iwge90l wrote

How do the spinning cams opening the valves not wear out/get smaller from hitting the valves several thousand times a minute?


Brandon432 t1_iwgreof wrote

This animation/video is a bit simplified. In real life, a couple things are different. The part at the top of the valve (or linked via pushrods and rockers) that actually contacts the camshaft is called the tappet. Tappers can be “flat” (not literally, they still have a bit of crown) or roller style. In either case, the tappet is made of friction resistant alloy and does NOT break contact with the cam. It follows the entire lobe so there is no “striking” just rubbing. Roller tappers greatly reduce friction but increase mass. In either case, the cam and tappets are enclosed in the engine head and continually fed motor oil to reduce friction and dissipate heat.


amazn_azn t1_iwgj8wo wrote

This is moreso "what an engine looks like while running" than what actually makes the engine work. The thermodynamic cycles are how engines generate mechanical force from the thermal energy released in the combustion of gasoline molecules.


Oaskary t1_iwgm3wt wrote

I'm so glad I don't have to invent an engine.


witzed1 t1_iwgnrd3 wrote

Strange valve timing gear configuration. Usually cam and crank turn in same direction. Maybe a model artifact but definitely not representative of modern engines.


Brandon432 t1_iwgpj1w wrote

They are turning in the same direction. Counterclockwise as viewed from the left.


Strength-Speed t1_iwgp260 wrote

Just a question if anyone knows. The cycle is intake, compression, ignition, exhaust. That would seem to indicate the piston starts in the up position then draws in air-fuel as the first step. But what draws the initial piston down, before the engine starts, as no ignitions have happened yet?


Brandon432 t1_iwgpf51 wrote

Starter motor aka cranking motor. That’s the sound you here when you cold start a car. The pistons rotating without igniton.


Stagamemnon t1_iwgpnas wrote

Yeah, but where’s the fleeb? Don’t you have to rub that cause the fleeb has all the fleeb juice?


krinklekut t1_iwgwujo wrote

Ah. Makes perfect sense now....


69poop420 t1_iwgzyan wrote

I think about these kinds of things at night and forget to follow up to see what they look like. Thank you.


spiderborland t1_iwh5elh wrote

What I choose to not research and just assume "mmhmm, gaskets and low clearance, yep" is how the top of the orange has gas in it, and the bottom of the orange has oil in it, and in a perfect world, they don't mix.


adampsyreal t1_iwhynx1 wrote

Nothing like a straight three.


Brucie67 t1_iwtwyo2 wrote

When you put it like that you make it look so simple.


mellbs t1_iwfbp3b wrote

Much easier to demonstrate with a single cylinder, and the diagram needs an element depicting airflow in its different stages


Lille7 t1_iwh1bjz wrote

Its a model sitting on a table, not diagram.


mellbs t1_iwh39zi wrote

Oh yea didnt realize this was an actual video and not an animation. I still dont think it adequately explains whats happening to today's average person.


thebeardknowstoomuch t1_iwfrap4 wrote

I don't know how an engine works and, after watching this, I still don't know


spinjinn t1_iwfymu7 wrote

There are four pieces to the sequence. They are faking them with just three.


yodazer t1_iwgbyqz wrote

How a 4 stroke* engine works. Your weedwacker does not work like this.