Mechanical Engineers of Reddit, why are the parts of engines which are bolted together, requiring gaskets, typically flat? Wouldn't a stepped surface (think Tetris) be stronger in regards to gasket wear?

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Bowwowchickachicka@reddit (OP)

Could they not be manufactured to match the shape?

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Fossilmorse@reddit

This happens with cam cover seals, the have a 90 degree corner to go over the cam caps on either side.

They often leak

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eeeBs@reddit

Or "seep" and the dealership wants $3k to fix it. Just let it seep.

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eeeBs@reddit

My water pump seal is leaking. $2200 to fix, but a gallon of coolant a month is like $30.

On a 9 year old, $12k car.

I'm considering doing the fix because it makes a mess and I can do the thermostat too while I'm in there, but, it's right on the edge of "do I really need it?"

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Mangonesailor@reddit

Every corner is a weak point in a gasket.

Your theory works for close-tolerance mechanical seals (look up graphite mechanical seals for pumps), and similarly for steam turbine end seals called a "labyrinth seal."

But for engines and such the next upgrade from a regular flat gasket is an o-ring, but that would mean the part cannot warp and must be rigid.

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You'd also need to make every bigger to fit the interlocking teeth... you can't mill into the engine block next to the cylinders to add a recess for the teeth on the head for fear of weakening the cylinder wall

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Bot_Fly_Bot@reddit

Sure they could, but those bends are still going to be weaker than a continuous flat gasket. And manufacturing something like that is expensive.

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super_starfox@reddit

Adding to this (for OP), "gasket maker" is a common thing and comes in a tube like toothpaste or glue.

Please do not use it on your teeth.

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evileagle@reddit

RTV is not suitable for all situations.

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super_starfox@reddit

Oh, definitely, and appreciate the clarification. It's a thing, but if OP looks into it... Definitely do some homework!

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orthopod@reddit

Sure, but now you have 3 dimensions to work about precise fit, instead of only 2.

If you need a gasket, despite being able to match and mill surfaces to 1 one thousandth of an inch, then trying to get a good fit with another dimension will be incredibly difficult.

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FrumundaThunder@reddit

Engines like the 1.5L 4 cylinder eco boost do have bent and curved gaskets for their valve covers. They require anaerobic sealant (gasket maker) for corners points where the gasket changes.

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Chippy_TheMonk@reddit

Hitting the tolerances to have all the different matting faces match would be difficult and costly. Flat is cheap and easy to do.

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SawDustAndSuds@reddit

Stresses will always concentrate at a corner or bend

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akaFxde@reddit

How would something like that be packaged? Wouldn’t be with it

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Bowwowchickachicka@reddit (OP)

Thank you all for your insight. Makes good sense to me now.

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bossesarehard@reddit

Some engines deisels and top end racing motors have a boost ring basically a small hope around the edge of the poison to increase headmaster performance. To hold 80 to 150 lbs boost in diesel or 40 to 80 in a race motor. Running methonal or even e85 or alchol in some cases.

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68Cadillac@reddit

Answer: Cost of manufacture. Machining male and female mating steps on parts is expensive. It's cheaper, by far, to machine the parts 'good enough' flat and throw a gasket in there to make up the tolerance.

It is possible to machine engine parts flat enough that you don't need gaskets. Issue is, do you want to pay for that? A good mill can get stuff flat within +/- 0.0002" (+/- 0.01 mm) over measured over 12 inches. A good surface grinder can get stuff flat within +/- 0.00001". That's over a magnitude flatter. And the price goes up over a magnitude.

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Trebescoot@reddit

Cost is the right answer, hot rodders will machine grooves in the head and block to receive fire rings. It massively increases cylinder pressure capability given you have enough clamping force. I also wanna say it was jaguar that thought they could make their tolerances tight enough to not need a gasket on their water pumps? Maybe it was a 70's thing. Ive also heard too mean jokes comparing German and British engineering.... So maybe it was just a rumor lol

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sockalicious@reddit

I had thought that if you mated two steel parts that were quarter-wave flat light that, that there was a pretty good chance they'd cold-weld.

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Roast_A_Botch@reddit

Not in atmosphere as oxides will be forming as soon as the surface is exposed preventing a cold weld no matter how flat you machine the surfaces. There are cold-weld processes done on earth but under ultra-high vacuum in expensive to operate labs and isn't even practically affordable for assembling W16 or Ferrari engines due to cost.

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Equana@reddit

What you are suggesting would be very expensive to machine. A flat surface is cheap and easy. A groove to fit an O-ring is only slightly less cheap but it makes a very effective seal.

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ThirdSunRising@reddit

Thermal expansion is the basic problem. There’s no way to eliminate the flexible gasket because it’s connecting parts that are expanding at different rates.

Stepping the gasket makes things a lot more expensive but doesn’t necessarily improve anything.

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SpeedyHAM79@reddit

If you have a bend in a gasket you will have uneven pressure across the gasket face, which reduces the sealing ability. It's best to have an even pressure across a gasket to ensure the seal is constant all around.

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owensurfer@reddit

The reasons here are well stated, cost, ease of manufacture and performance are quite good with flat surfaces. Tolerances for a complex surface would be harder to manage. Imagine what servicing a convoluted surface would take? Cleaning, resealing? A nightmare.

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PMBrewer@reddit

It’s just not cost effective or efficient the extra weight would kill any power gains you would have rather than just making two smooth surfaces.

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buildyourown@reddit

It's harder to get a stepper surface flat. A head can be cut in one fast precise cut. A step would take a long time with small tools and not be flat. It would also be very hard to recut in the future.

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juwyro@reddit

Flat is easy to make and seal, though grooves for o rings also work well.

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kevan0317@reddit

And flat lets different materials expand at different rates.

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ASDFzxcvTaken@reddit

This i would think is the biggest issue that a gasket has to contend with. Heck even within the same material hot spots and cooling areas expand within the material at different rates, so if there is an edge you're going to have a real bad time.

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kinecty@reddit

The real question here is why don't they do a better job of venting the crankcase or applying a negative pressure to the crankcase on turbo engines to prevent premature gasket failure.

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Leafy0@reddit

Flat is easy. Oring grooves in metal take more effort and time. It’s why you’ll typically see plastic and cast metal parts with the groove molded in, and the mating surface as flat piece of metal.

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Choice_Macaroon6805@reddit

Gaskets have this really awkward tendency to not like any angle other than flat.

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zmannz1984@reddit

I think it is easier to have flat surfaces seal against one another using simple compression of a gasket when the materials on each side are likely to expand and contract at different rates. I have made some parts for my own projects that used an interlocking sealing method that leaked after several heat cycles.

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PotatoDrives@reddit

Machining a flat surface is easy/cheap.

Machining a stepped/contoured surface is difficult/costly.

Machining mating surfaces that are stepped/contoured is extremely costly.

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So_Full_Of_Fail@reddit

In performance applications where you have real high cylinder pressures, you typically groove the head and block surface, and insert a wire ring to one side.

Which is effectively what you're asking about, and is indeed for better sealing to high pressures.

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Chippy_TheMonk@reddit

There is no added mechanical advantage. Clamping force is the same or even lower for the stepped design because of the resistance trying to hold the gasket around an edge and the vertical faces sliding past each other.

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Hedgesmog@reddit

In addition to the other comments here, gaskets in any design are often compressed, and have to yield a little when doing so to get a good seal.

Usually this compression happens in the direction things are clamped (e.g. the direction the bolts go). Imagine having a "U" shaped gasket... Minimal variations of the distances between the "sides" of the U from one engine to the next would make for inconsistent compression and therefore sealing performance.

Sure you might be able to do it if all the engines were identical. But tighter tolerances cost more money.

It's all about cost effective performance.

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Middle-Jackfruit-896@reddit

Why would a stepped surface be better for gasket wear? The step would create an edge that would impart a stress concentration on the gasket.

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tlk0153@reddit

It’s difficult to make so engines will cost more. However, having sections of two parts fit like a jigsaw puzzle forming metal seals is also not uncommon.

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Dnlx5@reddit

Because flat gaskets work and are cheaper.

BUT! Some are like that. Many valve cover gaskets are stepped.

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jcforbes@reddit

To kinda pile on, slightly rephrase, and also add to what's been posted:

-Flat surfaces are far cheaper to manufacture

-Gaskets with intricate shapes are more difficult to reliably manufacture which also means more expensive

-The big one... Why? Good paper, rubber, or liquid/adhesive gaskets last decades or more. Why would you change what already does a great job?

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campbellsimpson@reddit

Depends on the surface and the gasket material!

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themontajew@reddit

They us both, in the same engines a lot of the time.

It’s application specific, and “better” isn’t always better than “good enough”

Oil pans can be stamped, put a sheet gasket on, let it flex a bit to seal everything, it doesn’t matter, it’s not under pressure.

It’s easier to just flatten a surcafe than to cut a gland in it, it’s also harder to damage to the point of not sealing.

Inside of parts you’ll see a lot more O ring type seals, or if there’s high pressure.

My exhaust manifold uses a metal gasket because it gets hot as hell

Fuel injector lines are a shitload of PSI, so they get copper washers instead.

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ramdonghost@reddit

Some engines use controlled break in rods. But gaskets are necessary in many joints for the flexibility, this allows for a controlled pressure in the bolts. This is especially true for parts that might be disassembled multiple times, like an exhaust manifold.

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