How are engines made?

Like most people (in this country, anyway) I’ve seen clips of engine blocks being made in the 1920s. Lots of molten metal being poured into moulds. I remember something about sand casting. But engines made the better part of a century ago were simpler than the ones we have now. Even then, not having had the opportunity to dissect an engine modern or new, I wonder how the internal passages are made. I assume water jackets are more complex now. And I’d venture to guess that oil passages are pretty complex too. And sand casting? I can see how they would be useful for low volume production. But how can many thousands of identical engines be cast?

I know the blocks are still cast. The bearing journeys, some oil passages and other areas are machined afterwards.
No two blocks will be exactly the same, 'cept maybe the cubic inch part of it wich is precisely machined out of the cast block.

I can’t ask Dad (who’s been dead since '75), so they may not even still be using sand, but I can assure you that you can produce a whole lot of engine blocks using sand casting. As of the early 1970s, all blocks coming out of Detroit (or, I guess, Saginaw, Dearborn, and Hamtramck) were sand cast blocks. It is actually a rather efficient method for high volume production. Sand and resin is mixed and formed under pressure, subjected to some minor milling of its own, and sent directly to the casting line where the blocks are poured. As soon as the blocks have cooled sufficiently, the sand is knocked off the blocks and the resin and other oils scrubbed out, then the washed sand is recycled back to be mixed with resin and formed into new blocks. (Enough sand was lost in the process to require frequent augmentation from sandscrapers plying their trade in Saginaw Bay, but most of the sand was recovered and reused many times.)

My understanding is that aluminum blocks are cast using steel molds (or some steel-based alloy), but Dad was only tangentially involved in the very early aluminum blocks and I never got to see that process. Sand may have been replaced in the ensuing 35 years, but there was nothing about sand that hindered mass production or high volume lines.

Production internal combustion engine blocks and cylinder heads are still sand cast from either iron or aluminum alloy, and I imagine other parts are die cast . For drag racing, there are specialist machine shops making heads from solid aluminum chunks using CNC machines, and at least one firm making blocks this way.

The latest Chevrolet modular 4/5/6-cylinder inline engine is cast using a lost-foam process, which allows greater flexibility in shapes and yields castings closer to final shape for less secondary machining.

Hope you’ll accept Wikipedia for the cites.

Speaking as someone who’s worked in a foundry, I can tell you that engines are most definately still made by sand casting (In fact, “freeze plugs” are really holes left in the block so that the sand from the cores can be removed from the engine after it’s cooled.). There’s simply no better, or cheaper way of doing it. Yet.

The finish castings will have to be machined, since castings can’t hold exact tolerances, but that cost is minimal in comparison to what it would cost to machine an engine out of solid stock. An engine, if you think about it, is mostly empty space, and a cubic foot of steel weighs roughly 500 lbs. So if your average bare block (i.e. no heads, pistons, cranks, etc.) weighs 100 lbs and is 2 cubic feet in size (pulling numbers somewhat out of my ass, but not completely), then if you were to try to machine it out of solid stock, you’d need 1000 lbs. of steel, plus a machine that could handle the weight, and lots of expensive, specialized tooling to get into all those nooks and crannies. Once you were done, you’d have 900 lbs. of steel chips to dispose of, plus lots of worn out tooling to replace. With castings, you can do away with most of that waste, and easily recycle the leftovers.

This will, however, eventually change. Right now, it’s possible to make small objects out of metal in a process similar to stereolithography, and as the costs of the equipment come down, you’ll see more and more things made using that process. I don’t know if engine blocks for your average Honda Civic or Chevy Bland-O-Mobile will be produced that way, but certainly, the blocks for high performance cars will be.

They are still cast, though the modern technique uses disposable foam patterns, as opposed to the reusable wood patterns of the past. I think Saturn was one of the pioneers of this.

It’s rather skimpy, but here is a link to the wikipedia article on lost foam casting

In addition to the capital cost, the process is slow, finish and dimensional control is poor, and material choice is quite restricted. Aluminum in particular is a difficult material for all of these deposition processes. Titanium is one of the favorable materials, though, so aerospace applications with big budgets and low volume suit the process well. As a former insider, I’d be very surprised if the technology became ubiquitous enough for the automotive industry, including exotics, in my lifetime…well engine blocks anyway. There just might be a couple fellows making valves for racing applications already.

  1. Are any modern engines made by building up from seperate pieces? The 1930’s Crosley used an engine made by screwing cylinders into a base block. This was for air cooled engines, was the technique useable for water-cooled engines.
  2. the 1920’s Bugatti 12 cylinder engine was made by machining down a single cast block of steel-that must have been a big job-have any modern engines been made this way?

The old 4-cylinder, air-cooled Volkswagen engine in the Bug was made that way. There was a central aluminim crank case on which the cylinders were mounted by long machine screws. One of the easy things to do was to strip the threads in the block when installing the cylinders. Then you had to use a Helicoil[sup]R[/sup] insert to hold the screws.

Reminds me of my old BSA 650cc

But I used bolts and extra long studs with nuts at both ends to avoid the steel/alloy problems.

It helped that after Imperial my father did an apprenticeship at Napiers, and was a real hound when it came to rescuing potentially jettisoned parts.

Mixing metals and threads is asking for trouble, it is like mating monkeys with kangaroos.

I recall reading somewhere that Cadillac engine blocks in years past were set aside after casting for quite a while prior to machining to allow for tighter tolerance (such as it was), supposedly this gave time for any stresses built into the casting to work itself out. Sounds like a waste of space and inventory to me…

I think that’s true of all castings that are later to be machined to hold tight tolerances. I think there is quite a period of “relaxation” required for large castings to get to final shape and size.

Any materials specialists out there?

AFAIK, it’s possible to buy “seasoned” engine blocks, generally for hi-peformance applications. It’s time consuming and expensive, so it’s not worth it for normal applications. The blocks are heated in an oven for a couple of days, with the temperature increasing and decreasing slowly. I assume this is done before the final machining process, but I could be wrong. Before that started, guys usually used junkyard blocks. However, I remember reading that some guys who were running the same engine block in their tow truck (or other personal vehicle) would periodically buy a new engine for their tow truck and use the old tow truck block in their race car. Kills two birds with one stone.

Nearly all light aircraft engines are made this way. Aluminum cylinder heads are an interference screw fit on steel cylinders. The cylinders have a flange that bolts to the crankcase.

This is also a common design approach for motorcycle engines.

On the VW engines, I thought the crankcases were magnesium, No?

Only a few years, IIRC. Magnesium has the annoying habit catching fire when it gets too warm.

Very well could be. They were, and are, one of the two. In any case the hold-downs were torqued right up the the limit. You need an accurate torque wrench because if you go over the specified torque by just a tad; “Click,” and the screw starts to turn real easy like.

But maybe that’s OK. In my opinion, the repair with Helicoils resulted in a stronger thread.

Not quite the same as bolt-on cylinders, but the horizontally-opposed “boxter” engines (as used in Subarus, Porsches and some large motorcycles) are made of two essentially mirror-image halves bolted together, split along the axis of the crankshaft.