Tomislav Skračić, MA Undergraduate English Course for MARI NE ENGINEERS 3rd Semester

1. Tomislav Skračić, MAUndergraduate English Course forMARINE ENGINEERS3rd Semester Essential reading: SPINČIĆ, A., PRITCHARD, B., An English Textbook For Marine Engineers 2, Pomorski fakultet, Rijeka 2009. LUZER, J., SPINČIĆ, A., Gramatička vježbenica engleskog jezika za pomorce, Pomorski fakultet, Rijeka 2003.

2. Lesson 2 – Review The cranks of a multi-throw shaft are set at appropriate angles giving a “firing order” for the engine. The firing order is chosen primarily to obtain a smooth torque and the best mechanical balance. However, main bearings loads, exhaust arrangements suitable for turbocharging and torsional vibration may also be taken into account. Although the crankshaft appears to be robust, they rely on the main bearings to develop their full strength. When a crankshaft has to be handled outside the engine, it should be carefully supported to avoid high bending moments on it by its own weight. In the engine it is essential to ensure that the bearings carrying it are in good alignment, as bearing misalignment will cause the crankshaft to bend and eventually break it.

3. Lesson 2 – Review The main bearing shells are made of steel with a lining of bearing metal which can be white metal, copper-lead or aluminium-tin alloy. A thin flash of lead or indium is often added to provide a layer giving protection against corrosion. The shells are held in position and shape by seatings of the bedplate or frame.To ensure efficient and reliable operation the crankshaft should be checked periodically for alignment by measuring the deflection of the webs.

4. Lesson 2Review: Complete the following text The crankshaft, which converts the __________ motion of the piston to rotating motion, must resist the __________ stresses caused by the connecting rod __________ when the piston is at the top dead centre. Then the maximum gas pressure acts straight down on the __________ and tends to bend the shaft between the adjacent __________ . The crankshaft must also __________ the torsional forces produced by the change of speed.

5. Review: Complete the following text Medium speed engines have crankshaft usually solid __________ , i.e. made from a single piece, while slow speed engine crankshafts are mostly of semi-built design with crankpins and __________ forged or cast in one piece and shrunk on to the __________ . The type of steel used, which is carbon or alloy steel containing nickel, chromium and molybdenum, is chosen for its strength, resistance to __________ and hardness of bearing surface.

6. Main Bearings LOCATION In the transverse saddles of the bedplate. PURPOSE To provide support for the crankshaft.

7. Main Bearings • MATERIALS • Used for crankshaft bearings and connecting rod big end bearings (4-stroke engines) • Steel support shell (basic element); • Bearing metal (white metal, copper-lead or aluminium-tin alloy, leaded bronze); • Nickel barrier (separating the two layers); • Galvanized layer (good running-in and dry running properties) • Anti-corrosion layer (lead or indium)

14. Main Bearings • PARTS • Upper and lower shells(fitted in bedplate seating / saddle) • Thrust bolts • Covers • Shims(for adjusting vertical bearing play)

20. Main Bearings • CLEARANCE • Measurement • lead wire • wear gauge / bridge gauge • feeler gauge • “kjaer“ feeler • Adjustment • This can be taken up by reducing the thickness of shimsbetween the bearing butts and the housing.

21. Main Bearings • DAMAGES • Indications • increased temperature • slight oil pressure drop(sometimes followed by noise) • Kinds • Squeezing of the overlay / white metal(problems with oilfilm formation); • Fatigue cracking(due to poor quality, shaft misaligmentor local overload); • Dislodgement of overlayor white metal (due to cracking); • Scoring(striationdue to presence of hard particles); • Wiping(misshapedoverlay or white metal due to hightemperature)