Aluminum Engines: What Prevents Warping?

[Xyius]

Hello all,

Most engines today in passenger cars are made out of aluminum instead of iron. I am confused about the fact that aluminum is lighter than cast iron and warps easier under extreme temperatures. How do they stop this warping from occurring?

 

[Simon Bridge]

By manufacturing within the tolerances of the materials and using alloys.

 

[OldEngr63]

Some aluminum blocks use cast iron sleeves for the cylinders to take the most severe heat.

 

[jack action]

Here's one method described in the COMPLETE VEGA HISTORY 1970-1977:

Vega's most unique feature was its 2.3 Liter (140CID) OHC four-cylinder
engine. Unlike previous GM aluminum engines, the Vega block did not have
cylinder liners. GM Research Labs had been working on a sleeveless
aluminum block since the late 50's. The incentive was cost. Getting rid
of those liners on a four-cylinder block would save $8, which was a lot
of money back then. This involved a joint venture between the GM labs,
Reynolds Metal Company, and Sealed Power Corporation. Reynolds came up
with an alloy called A-390, composed of 77 percent aluminum, 17 percent
silicon, 4 percent copper, 1 percent iron, and traces of phosphorus,
zinc, manganese, and titanium. The A-390 alloy was suitable for faster
production diecasting. These qualities made the Vega block less
expensive and easier to manufacture than other aluminum engines! A
process of etching the cylinder block walls exposing the silicone
particles insured a wear surface stronger than steel. Sealed Power
developed special chrome-plated piston rings for this engine that were
"blunted to prevent scuffing. The large bore, long stroke design
provided good torque and lower engine RPM for reduced wear. A cast iron
cylinder head was chosen for low cost and structural integrity, and an
overhead cam was specified.

I re-read the OP and found out that you worry more about warping than wear.

The first engine part to be made of aluminum were the pistons. Those didn't warp. Then, they made the cylinder heads. They didn't warp either. Even though these two parts constitute the walls of the combustion chamber. Doing the block afterward is a breeze (warp-wise), since it is subjected to less heat as the piston moves down. Wear is more of concern.

If a piece is thick enough, it won't warp (and piston tops and cylinder heads are thick). If you made the cast iron engine thin enough, it would warp too, as you can see with this skillet (source):

​

 

[Simon Bridge]

Aluminium engine parts are more prone to warping than the equivalent steel part if something goes wrong - so the other way to answer this question is "they don't" (stop the warping from occurring). But this is a bit simplistic - the cooling system in aluminium engines is critical, and other strategies like alloys and sleeves (iron, steel, or ceramic) are used.

Note: the Corvair used to have a rep for stripping cylinder heads ...

It's difficult to know how to answer the question properly because it is so easy just to google for the basic stuff.
eg. http://en.wikipedia.org/wiki/Aluminium_alloy#Aluminium_alloys_versus_types_of_steel

Also: "build in better cooling", is pretty much the answer included in the question.

 

[Xyius]

Sorry for the late reply! Thanks guys!

 

[mfb]

Just a comment on alloys: you can find pure aluminium about as often as pure iron (instead of steel): not at all. It exists for some special applications, but basically all consumer products have some other elements mixed in.

 

[Auto Engineer]

Not directly related to this thread, but made interesting reading for a current problem I had with a part of an automotive engine, alloy timing chain housing, a stud sheared off and in our trade we have always applied heat to the alloy to try and loosen the stud/bolts, but in this example the stud sheared again. Reading the research from the link provided helped me to understand that as alloy ages and working temperatures change over time, the alloy material structure changes and hardens, thus no oxidation or corrosion needs to occur because the alloy alone will harden around the mild steel bolt/stud and can make it practically impossible to remove after a long ageing period.

Freezing the alloy seems to be the better option to try and remove studs/bolts, but assume is costly?