In the last Greasy Bits, we introduced the engine’s cylinder, piston, connecting rod, and crankshaft. Now we will add the crankcase, which is the skeleton all these parts either bolt to or live inside. The crankcase is aluminum and cast in two halves. That allows placing the crankshaft and camshaft (we will describe the camshaft later) inside the crankcase, then bolting on the other half.
You will just as often hear simply “the case” or “engine case” around the airport when referring to the crankcase.
Furthermore, the top of the cylinders is covered by the cylinder head, which, as noted last time, contains the intake and exhaust valves along with the spark plugs. Typical aviation engines have individual cylinder and cylinder head assemblies joined together at birth and never taken apart thereafter. Most aviators call these assemblies “cylinders” while a few call them “heads,” plus there are various slang terms such as “jugs.” No matter the name, the assemblies are the same thing—a cylinder and head joined together. These assemblies are then bolted to the crankcase, typically four or six at a time. There is an eight-cylinder Lycoming and all sorts of multi-cylinder radials and other engines, but for now, we will stick with the ubiquitous four- and six-cylinder Lycoming, Continental, and Rotax variants.
Let’s also note automotive practice is to house all the cylinders in one casting called the engine block. A separate cylinder head is bolted to the block, and this automotive-style head typically covers three or four cylinders in one casting.
In air-cooled aircraft engines, the cylinder heads are individual castings both threaded and thermally shrunk onto individual cylinders (one part is chilled and the other heated when threaded together). The cylinders are steel; the heads are aluminum. Once screwed and shrunk together, they cannot be taken apart without destroying either piece, so they are serviced as a unit. This means you can change a single “cylinder” on an airplane engine (often done), whereas in an automotive engine, the whole engine is rebuilt at the same time (if it ever is rebuilt).
The rest of the engine is a series of systems such as the lubrication, intake, exhaust, ignition, valve train, and so on. Next time, we will introduce the cooling system.
Superior Engine used to have a a program, during which you assembled your engine, under the watchful eye of one of their technicians, at their factory in Texas. I figured what better way to be able to inspect & maintain my engine, than to have the intimate knowledge gained by putting it together over 3 days and see it run on the dynamometer. So my son & I did – worth every extra penny it cost. Wish every engine factory did so.
What are those taps/plugs on the lifter bores? Provision for external oil lines??
Guessing those help hold in or keep the roller tappets from turning themselves in their bores. Someone else can correct me if wrong.
Interesting. Lycoming doesn’t use anything like that externally. Sure looks like AN plugs to me.
M Long is correct. Superior engines with roller tappets use a small bolt to stop lifter rotation.
Hmm, so is the lifter slotted to accommodate lateral movement?
Superior’s roller lifters can be removed without splitting the case. The slot and screw keep them in place while allowing lifting motion.
https://www.superiorairparts.com/downloads/serviceletters/L08-01.pdf
As a non-technical person I very much appreciate this series… short reads that use plain English! Too many times over the years I’ve read any number of engine articles that use all kinds of terminology not explained and have illustrations pulled from an FAA document (copyright free and cheaper than making your own) that have all kinds of parts labeled that are not part of the subject and/or parts labeled with names different than those used in the text.