A mechanic disassembles a cylinder and finds two types of piston rings: one set with a tapered face near the top of the piston, and a slotted ring with a spring expander near the bottom groove. What are the respective functions of these two ring types?
- ABoth ring types perform oil control; the tapered ring is for high-temperature areas only
- BThe tapered ring seals combustion gases (compression ring); the slotted ring with spring expander scrapes and controls oil film thickness (oil control ring)
- CThe tapered ring controls oil; the slotted ring seals combustion pressure
- DBoth rings are compression rings, positioned differently to distribute wear evenly
Show answer & explanationAnswer & explanation
Correct answer: B. The tapered ring seals combustion gases (compression ring); the slotted ring with spring expander scrapes and controls oil film thickness (oil control ring)
Compression rings, often with a tapered or barrel face, are located in upper grooves and seal combustion gases against the cylinder wall. Oil control rings, typically slotted with a spring expander behind them, are located in lower grooves and regulate the oil film thickness on the cylinder wall, scraping excess oil back to the sump.
Why the other options are wrong
- A. Incorrect, the tapered ring is a compression ring, not for oil control.
- C. This reverses the actual functions of the two ring types.
- D. Both rings are not compression rings; their designs differ specifically for oil control functions.
Piston Ring Types
Compression rings seal combustion gases in upper piston grooves, while oil control rings, using a spring expander behind a slotted ring, meter oil film thickness in lower grooves.
- Compression rings often have tapered or barrel-shaped faces
- Oil control rings have slots or holes to return oil to the crankcase
- Ring type and position affect sealing, cooling, and lubrication
Memory trick: Top rings seal the fire, bottom rings control the oil