Reciprocating Engine Construction, Components, and Operation
Domain 2 covers the hardware that contains the cycle: crankcase, crankshaft, rods, pistons, cylinders, valve train, and accessories.
Load path and parts
- The crankcase carries main bearings and reacts firing loads; the crankshaft converts reciprocating motion to rotation and may include counterweights and a damper.
- Master and articulated rods are used in radial engines; opposed engines use one-piece or split rods.
- Pistons transfer gas force, carry rings for sealing and oil control, and are cooled by oil spray or fins.
- Cylinders may be steel barrels with aluminum heads; valves are opened by camshaft, lifters, pushrods, and rocker arms.
Fit and timing
- Valve clearance is measured cold at TDC on the compression stroke; intake and exhaust clearances differ.
- Firing order and valve timing are set by camshaft and crankshaft relationship; incorrect assembly can cause backfire or valve collision.
- Mean piston speed = 2 × stroke × rpm, with unit conversion required.
Worked example
A 5.5 in stroke engine turns 2700 rpm. Mean piston speed = 2 × 5.5 × 2700 = 29,700 in/min; divide by 12 = 2,475 ft/min. The factor 2 accounts for one up and one down stroke per revolution. This is a wear and stress indicator, not the piston's instantaneous speed.
Traps
Setting valve clearance on the wrong stroke; mixing intake and exhaust clearances; ignoring master-rod orientation; reusing torque-to-yield fasteners; assuming a damper is optional.