Bearings & Lubrication Roger Bortignon

1. Bearings & Lubrication Roger Bortignon

2. Friction Friction is… • the resistance opposing any effort to roll or slide one object over another

3. Causes of Friction • minute imperfections on surface interact • deformation or indentation of one object into another

4. Kinds of Friction 1) Fluid friction: is less than solid friction but it exists 2) Static friction: resistance to movement between 2 bodies in contact & at rest 3)Kinetic Friction: • Sliding friction: resistance to continued movement once set in motion • Rolling Friction: one body rolling over another – the least of the 3 frictions

5. Bearings • Purpose of a bearing: • reduce friction • support a load/rotating shaft • radial • axial • Bearing classifications: • friction bearings (aka: plain bearings) • anti-friction bearings

6. Friction Bearings • 3 types of friction bearings… • Journal bearing: crankshaft, piston pin, camshaft • Guide bearing: valve guide • Thrust bearing: • controls crankshaft end thrust 1

7. Friction Bearings • small 4 cycle engines use the engine parts as the wear surfaces • crankshaft connects directly to the connecting rod • camshaft spins directly in the engine block • larger engines use replaceable wear surfaces called… • precision insert bearings

8. Friction bearing advantages… • physically compact • high speed (rpm) capability • low cost • easily replaced • can tolerate greater levels of debris in the lubricant

9. 2 categories of anti-friction bearings… 1) cylindrical roller bearings (a) • used in radial & axial load applications • needle type (a) & tapered rollers (b) are variations of cylindrical rollers 2) ball bearings • are designed for radial loads & sometimes limited axial • offer lower friction levels than #1 a 2 b c

10. Bearing Surfaces • the rolling elements in a bearing roll on bearing races… • rolling elements are made from high-carbon chromium steel which also contains small amounts of manganese and silicon inner race outer race

11. More anti-friction bearings… • ball thrust bearings • needle thrust bearings

12. How do bearings reduce friction? • chief cause of rolling friction: deformation • steel wheel on steel rail: .002 Coefficient of Friction • riding a bike with a flat tire: very high Coefficient of Friction • this is why bearings surfaces are hard • bearings & their races are very hard •  smaller “footprint” & a lower Coefficient of Friction • this is a compromise between size & strength

13. Lubrication - Oil Lubricating oil is designed to… • Lubricate moving parts (minimize wear/reduce friction) by separating the two moving parts Engine oil is also designed to… • Cool engine parts by absorbing heat • Clean engine via detergents that are added to the oil • Seals the area between the rings and the cylinder wall to improve combustion • Quiets the engine by separating moving parts

14. Engine Oil • Oil viscosity: its resistance to flow or rate of flow. • Low viscosity oil = thinner (think baby oil) • High viscosity oil = thicker (think honey) • Viscosity Grade: determined by… • Society of Automotive Engineers (SAE) • lower numbers = thinner oil • higher numbers = thicker oil • Oil Service Classification: determined by the American Petroleum Institute (API) • refer to handout

15. Synthetic (man-made) Engine Oils 1) Synthetic motor oils willwithstand higher engine temperaturesthan petroleum based oils • 600°F compared to… • 450°F for petroleum oils 2) Synthetic oils will beginlubricating at lower temperaturesthan petroleum oils • -58°F degrees, compared to… • -35°F degrees for petroleum based oils 3) Synthetic oils are more “slippery” than petroleum oils • less wear and tear • cooler engine • better performance

16. Lubrication Systems • Splash Lubrication: • used with a “dipper” (horizontal shaft) • or “oil slinger” (vertical shaft)

17. Splash Lubrication Systems Continued 2) Barrel pump – common on many vertical shaft engines

18. Full Pressure Lubrication System • uses a positive displacement oil pump • pump feeds pressurized oil to bearing surfaces, camshaft, connecting rod and valve train • can be used in combination with splash system

19. Oil Filtration 3) Full Flow System

20. Lubrication - Grease • grease is oil that has a thickener added to increase its viscosity • lithium is often the thickener • rust and corrosion additives are added • “tackifiers” may it cling better to parts • antifriction additives such as Molybdenum may be incorporated • easier to seal in (and prevent leaks) than oil is • better than oils under heavy loads • it is designed to remain in contact with parts and lubricate as well • without being squeezed out between moving parts • or forced out from gravity or centrifugal force

21. National Lubricating Grease Institute NLGI Wheel Bearing Grease