Internal Combustion Engine (2021) • Hacker News Board

Re: Internal Combustion Engine (2021)

#31

Post by arlattimore » Wed, Jul 01, 2026, 7:08 PM UTC

LeifCarrotson wrote: post #28

arlattimore wrote: post #13

Earlier quoted context omitted.

The bearing surfaces in an engine (ex: crankshaft main bearings) have very tight tolerances, usually in the 15-25 thousandths of an inch. The engines oil pump fills those tiny gaps with pressurized oil which allow the metal surfaces to spin thousands of times per minute without damage. This is also why if you have any issue with oil pressure (ex: oil pump failure, cracked oil line) or oil starvation (ex: driving a re…

It's 0.0015, that's 1.5 to 2.5 thousandths, or 15-25 "tenths" as they're called. That's not a particularly tiny gap in the machinist world, it's large so that you can pump viscous oil in it and deal with a wide variety of temperature changes. 25 thousandths would be sloppy, a nominal clearance hole for a 1/4x20 bolt is about that much.

Good catch, sorry should have corrected that. While not small for a machinist, I think by the average persons definition that is a pretty small gap for the oil to occupy ;-)

Re: Internal Combustion Engine (2021)

#32

Post by raffael_de » Wed, Jul 01, 2026, 7:20 PM UTC

Toutouxc wrote: post #21

MarkusWandel wrote: post #12

Wonderful but it irritates me that so many descriptions of internal combustion engines refer to "explosions" of the fuel. You don't want that. It causes knocking and pinging and engine damage. You want a controlled burn that generates heat smoothly.

Not exactly. You do want a deflagration and not a detonation, but "explosion" is more loosely defined and, depending on who you're talking to, a self-sustaining subsonic flame front and a sharp pressure spike are a perfectly valid explosion.

explosion/detonation causes engine knocking or pre-ignition which is both very bad. a properly working combustion engine is driven by controlled burning.

Re: Internal Combustion Engine (2021)

#33

Post by nablaone » Wed, Jul 01, 2026, 7:23 PM UTC

WalterBright wrote: post #27

calmbonsai wrote: post #24

Earlier quoted context omitted.

Some engines are also substantially cooled by oil, but those are either older designs (think “air-cooled” Porche) or industrial prime-movers.

You are quite right, the oil also serves to transport the heat away.

It's a solvent also.

Re: Internal Combustion Engine (2021)

#34

Post by HoldOnAMinute » Wed, Jul 01, 2026, 7:31 PM UTC

lostlogin wrote: post #18

misiek08 wrote: post #5

Earlier quoted context omitted.

You meant - awful knocking combustion in the first, main animation? I never catches any real bug is those great posts, but this one, especially as first animation on the page - weird.

One of the rare situations where someone wants a bit of retard?

That is often more advisable as opposed to doing it fully.

Re: Internal Combustion Engine (2021)

#35

Post by pak9rabid » Wed, Jul 01, 2026, 7:39 PM UTC

londons_explore wrote: post #25

Worth noting the design of the internal combustion engine hasn't changed much in 50 years. The thing that has changed is the control systems. What used to be a primitive mechanical way of mixing fuel and air (the carburettor), is now an electronic fuel injection system, with the fuel air ratio very carefully matched to reduce pollution (fun fact: modern cars release so little carbon monoxide, you won't kill yourself…

There's also been advancements in cylinder head technology (i.e., VTEC, VVT, etc), which I guess also falls under control systems, but worth mentioning as these technologies are very cool. Honda's iVTEC has it down to a damn science with how to optimize valve lift & duration across the entire RPM spectrum.

Re: Internal Combustion Engine (2021)

#36

Post by jtwaleson » Wed, Jul 01, 2026, 7:39 PM UTC

I'm showing this page to my team and investors every couple of weeks. Visual, animated explanations are MUCH better than textual content for deeply grokking something. This is what we're trying to build for large software systems. I love the animations on this site so much, thank you for building them.

Re: Internal Combustion Engine (2021)

#37

Post by nickvec » Wed, Jul 01, 2026, 7:43 PM UTC

I hope Ciechanowski posts some more in the near future. He has some of the best "how does this work" articles I've come across.

Re: Internal Combustion Engine (2021)

#38

Post by toxik » Wed, Jul 01, 2026, 7:43 PM UTC

LeifCarrotson wrote: post #26

bob1029 wrote: post #7

> Presence of oil is critical here as it creates conditions for hydrodynamic lubrication. You can hear this effect in some vehicles at initial startup time for a few seconds. I know of certain Ford engines where it actually causes issues over time. The model years with auto start/stop have the worst of the cam rattle disease.

Auto start/stop isn't off for enough time for the oil to drain from the galleries and especially not out of the bearing journals. It's the first few seconds after an engine has been off for hours (or worse, for potentially years) that are the problem.

I thought it pretty well established that auto on/off is bad for the engine, as is intermittently turning off some cylinders as some do. Is that wrong?

Re: Internal Combustion Engine (2021)

#39

Post by bluedino » Wed, Jul 01, 2026, 7:48 PM UTC

bob1029 wrote: post #7

> Presence of oil is critical here as it creates conditions for hydrodynamic lubrication. You can hear this effect in some vehicles at initial startup time for a few seconds. I know of certain Ford engines where it actually causes issues over time. The model years with auto start/stop have the worst of the cam rattle disease.

That's the timing chain tensioners losing oil pressure.

Re: Internal Combustion Engine (2021)

#40

Post by vel0city » Wed, Jul 01, 2026, 7:49 PM UTC

toxik wrote: post #38

LeifCarrotson wrote: post #26

Earlier quoted context omitted.

Auto start/stop isn't off for enough time for the oil to drain from the galleries and especially not out of the bearing journals. It's the first few seconds after an engine has been off for hours (or worse, for potentially years) that are the problem.

I thought it pretty well established that auto on/off is bad for the engine, as is intermittently turning off some cylinders as some do. Is that wrong?

It sounds like you're talking more about systems that supposedly disengage some cylinders while the car is cruising. Some engines with that kind of technology have been known to damage cylinders for multitude of reasons.

That's very different from the start/stop feature they're talking about. That's about fully stopping the engine when you come to a complete stop like at a red light and then automatically starting again when you get off the brake.