Piston
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This document discusses piston design and failure analysis. Pistons are designed to transfer energy to the crankshaft and control expansion under warm-up conditions. Pistons have different types of heads and measurements. Piston failure can occur due to issues like heat seizure from excessive heat, cold seizure from thermo-imbalance, lack of lubrication, or piston dome breakout from ignition timing problems. Analyzing piston deposits and wear can help identify the root cause of failure.
Piston
- 1. Piston Design & Failure Analysis
- 2. Piston Function Transfer energy to the crankshaft. Control expansion under warm- up. 2
- 4. Piston Heads (Crown) Domed Flat Top Recessed (valve reliefs) Dished
- 5. A Domed Piston with valve reliefs or valve pockets.
- 7. A Flat Top Piston with valve reliefs or valve pockets.
- 8. A Dished Piston with valve reliefs or valve pockets.
- 9. Piston Measurements New pistons are measured at dimension “H” Used pistons are measured at widest point. 9
- 10. Piston Design Pistons are neither cylindrical nor round. Pistons are made with special materials to control expansion. Piston rings have special 10
- 12. Normal Pistons Deposits vary from oil ash, brown, tan, to black/brown. Light color denotes higher cylinder temperatures. Light scoring is normal, varnish from blow-by gas 12
- 13. Heat Seizure Excessive heat, over 1200F/650C EGT Lean jetting or adjustments on carb Incorrect loading on propeller 13
- 14. Cold Seizure Thermo- imbalance of piston and cylinder Lack of warm-up Excessive temperature 14
- 15. Lack of Lubrication Excessive water ingestion causing loss of oil film on intake. Lack of intake air filter service. Results in excessive clearance 15
- 16. Piston Dome Breakout Ignition timing failure, erratic firing. Lack of ignition damper, points engines. 16
- 17. Piston Fracture Complete disassembly required to remove all material. Cause from excessive wear, excessive RPM with no load, excessive clearance fitting. 17