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Engine Sealing, Gaskets, and Fastener Torque

Engine Sealing, Gaskets, and Fastener Torque. Chapter 51. Objectives. Order the correct gaskets for a variety of engine repair jobs Explain the theory related to torque and clamping force Understand the role that friction plays when tightening parts

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Engine Sealing, Gaskets, and Fastener Torque

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  1. Engine Sealing, Gaskets, and Fastener Torque Chapter 51

  2. Objectives • Order the correct gaskets for a variety of engine repair jobs • Explain the theory related to torque and clamping force • Understand the role that friction plays when tightening parts • Describe the differences between types of head gaskets

  3. Objectives (cont'd.) • Understand the theory behind torque-to-yield fasteners • Select the correct sealer for use in a variety of applications

  4. Introduction • This chapter deals with a very important area • Sealing lubricants and coolants within the engine • Leaks • Unprofessional • Lead to serious mechanical part failures

  5. Clamping Force • Avoid leaks by applying clamping force on two parts that are held together • Clamping force results from: • Tension or stretch on bolts securing two pieces • Springiness of a gasket between parts • Clamping force will change if threads are not clean and undamaged • Cleanliness is very important when assembling parts

  6. Torque and Friction • Torque • Measurement of twisting effort required to tighten a fastener • Amount of fastener clamping force changes with use of lubricants • 90% of torque applied in tightening a fastener is used to overcome friction • Final 10% provides clamping force • Fastener threads must be sealed and lightly oiled

  7. Torque Wrenches • Torque is measured with a torque wrench • Types • Beam wrench • Click (spring) wrench • Dial torque wrench • Torque measured in foot-pounds or inch-pounds • Metric measurement is Newton-meter • Digital torque wrenches • More expensive • Purported to be as accurate as dial torque wrenches

  8. Torque-to-Yield • Normal head bolt torque values • Calculated safety factor 25% less than maximum • Clamping force is 75% of potential for size • Head bolts • Produce clamping force of ±200% • Torque-to-yield • Tighten bolts to within 2% of yield point • Consistent clamping force and fatigue resistant • Work well with aluminum heads

  9. Torque by Degrees • Torque turn (i.e., torque angle) • Ensures equal tightness of fasteners • Method • Tighten the bolt to specified torque • Turn it additional 35 to 180 degrees • Torque angle gauge • Measures how far a fastener is turned

  10. Fastener Clamping Load • Preload • Clamping load on a fastener • Ways to measure preload • Torque wrench • Torque angle gauge • Measure bolt stretch • Both ends must be accessible

  11. Gaskets and Seals • Gaskets: installed between two surfaces to prevent leaks • Can be purchased individually or in sets • Modern head gaskets: difficult to seal • Non-retorque composite gasket: has facing, coating, and core • Graphite-faced gaskets: premium • Teflon®, moly, or silicone-based antifriction coating: seals minor surface imperfections

  12. Gaskets and Seals (cont’d.) • Metallic head gasket: single and multilayer • Multilayer steel gaskets more common as cylinder head gaskets • Gasket should be appropriate for surface texture • Surface texture: measured by roughness average • Copper head gaskets • Used for corrosive and high-vibration uses • No-retorque gaskets • Resistant to compression • Bolt stretch does not diminish clamping force

  13. Cleaning the Head • Clean before assembly • Use sharp scraper to clean iron head and block • Clean aluminum heads with plastic scraper • Abrasive bristle discs can damage engine • Never use with a die grinder • Do not use them on aluminum head with multilayer steel gasket • Do not use too coarse a grit • Do not clean “ghost marks” • Do not to clean in one area longer than another • Remove material thrown about by the discs

  14. Head Gasket Installation • Head gaskets perform most difficult sealing job • Sealing of combustion is very critical • Clamping pressure on bolts greater than combustion pressure • 75% of clamping load on head bolts used to seal combustion • Match new gasket to old one or to block and head • Cooling and oil holes do not match up: serious problems result

  15. Other Engine Gaskets • Other gaskets are used at several locations in the engine

  16. Valve Cover, Timing Cover,and Oil Pan Service • Valve cover gaskets: molded to shape of cover • Oil pan gaskets: made of several pieces • Sheet metal parts: often become distorted when tightening bolts

  17. Valve Cover, Timing Cover,and Oil Pan Service (cont'd.) • Cork used in vintage applications • Shrinks in the presence of air • Rubberized cork • Does not shrink • Silicone and neoprene gaskets are the best • Expensive, but sometimes reusable • Paper gaskets • Require sealer • Intake manifold gaskets • Must be resistant to air and water leaks

  18. Valve Cover, Timing Cover,and Oil Pan Service (cont'd.) • Exhaust manifold gaskets • Not usually found on new cast iron heads • Gaskets used once parts are separated for service • Bottom of exhaust manifold uses O-ring gasket • Chemical gaskets • Silicone or chemical sealers • Not used for head gasket or fuel systems gasket • Anaerobic sealers cure without air • Used only on precision machine parts

  19. Gasket Sealers • Gasket sealers purposes • Help gaskets seal • Hold gaskets in place • Substitute for gaskets • hardening gasket cements • Do not use as sealers in automotive applications • Anaerobic adhesive sealers (i.e., threadlockers) • Blue: parts may need disassembly • Red: parts not intended to be disassembled

  20. Silicone-RTV Sealant • Room temperature vulcanizing (RTV) (i.e., silicone rubber) • Cures when exposed to air • Many gaskets can be eliminated by using a bead of RTV applied by a robot • Sets faster in warm temperatures and high humidity • Develops skin in 15 minutes • Sets completely in a day

  21. Silicone-RTV Sealant (cont'd.) • Low-volatile RTV • Used on vehicles equipped with oxygen sensors • High-temperature RTV • Adding iron oxides to RTV increases its temperature rating by 50-100°F • Teflon® tape or liquid thread sealer • Threads can be sealed with Teflon® tape • Rubber cement sealers • Popular and easy to use • Thicken with exposure to air

  22. Seals • Dynamic seals (i.e., chevron seals) • Seal moving parts • Seal installation • Several items of concern • Front seals • Usually lip-type seals with a garter spring • Camshaft seals on OHC heads • Located behind camshaft sprocket(s)

  23. Rear Main Seals • Leaking rear seal • Can destroy a clutch • Newer engines use neoprene lip seal • Be sure crankshaft rear sealing surface is clean and smooth • Sealer must be applied to flywheel bolts to prevent oil leakage from interior of oil pan

  24. Transmission Front Pump Seal • Keeps transmission oil from leaking between torque converter and transmission oil pump • Becomes brittle with age • If seal fails: transmission fluid leaks from between engine and transmission • Often replaced as preventative when engine overhauled

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