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EXAMPLE STUDY 3,000 miles after the shop had rebuilt the engine in a late-model Toyota, the customer returned the car complaining of abnormal noise and vibration coming from the engine. She also said it seemed like the engine had a "miss." The technician who did the engine work was experienced and was quite sure he did everything right. The car was taken on a road test and the problem was verified. The noise and vibration varied with engine speed and the engine just did not seem to run right. The vibration seemed to be caused by a loose, damaged, or broken engine mount. So a careful inspection was done. No problem was found with the mounts. Next, the technician connected a scan tool to see if there were any hints as to why the engine vibrated or had a miss. No codes were retrieved. A thorough inspection was done on everything under the hood. Nothing was obviously broken or disconnected. He started the engine and looked around it. This is when the potential problem was noticed. The harmonic balancer was wobbling on the shaft. Turning off the engine, he reached down to find that the attaching bolt was loose. He knew he had tightened it during the engine rebuild so the fact that it was loose was a mystery. He proceeded to tighten the bolt, but checked the torque specifications first. This is when he discovered what he did wrong. The bolt should be tightened to a little over 200 ft.-lb. He knew he did not tighten the bolt that much. To do this, the balancer and crank shaft need to be held stationary while turning the bolt. The balancer, crankshaft sprocket, and woodruff key were inspected. These were not damaged yet. He borrowed the special tool to hold the crank and tightened the bolt. The engine was started and the problem disappeared. The technician was actually lucky; the wobbling balancer could have caused serious damage to the crankshaft. On this engine, the crank sprocket and harmonic balancer share the same woodruff key. This is the reason for the required bolt torque. The engine miss was caused by the wobbling balancer. The rotation of the crankshaft sprocket is monitored by the crankshaft position sensor, which is located next to the sprocket. The sensor, reacting to the wobbling of the sprocket, sent erratic readings to the engine control module. These unstable signals were enough to cause the miss but were within the normal range so the system did not set a trouble code. The technician learned once more that following the recommendations of the manufacturer can save time, frustration, and reputation. TERMS Babbitt Backlash Boring bar Cam follower Cast Chamfering Core plug Deck Dome Duration Flexplate Flywheel Forge Full-round bearing Gear-type pump Glaze Harmonic balancer Head Hone Hypereutectic Leakdown Line boring Long block Overlap Piston pin Piston rings Piston skirt Plastigage Ring lands Rotor-type pump Short block Split bearing Taper Tappet Total indicator reading (TIR) Valve lifters Variable valve timing (VVT) Wrist pin SUMMARY ¦ The basic short block assembly consists of the cylinder block, crankshaft, crankshaft bearings, connecting rods, pistons and rings, and oil gallery and core plugs. On OHV engines the camshaft and its bearings are also included. ¦ The cylinder block houses the areas where combustion occurs. ¦ A properly reconditioned cylinder must be of the correct diameter, have no taper or runout, and have a surface finish such that the piston rings can seal. ¦ Glaze is the thin residue that forms on cylinder walls due to a combination of heat, engine oil, and piston movement. ¦ Core plugs and oil gallery plugs are normally removed and replaced as part of cylinder block reconditioning. The three basic core plugs are the disc or dished type, cup type, and expansion type. ¦ A cam changes rotary motion into reciprocating motion. The part of the cam that controls the opening of the valves is the cam lobe. The closing of the valves is the responsibility of the valve springs. ¦ Solid valve lifters provide for a rigid connection between the camshaft and the valves. Hydraulic valve lifters do the same but use oil to absorb the shock resulting from movement of the valve train. Roller lifters are used to reduce friction and power loss. ¦ The camshaft is driven by the crankshaft at half its speed. ¦ The most common ways to measure cam lobe wear are with a dial indicator or an outside micrometer. The dial indicator test should be con ducted with the camshaft in the engine. When using an outside micrometer, the camshaft must be out of the engine. ¦ Most premature cam wear develops within the first few minutes of operation. ¦ The crankshaft turns on a film of oil trapped between the bearing surface and the journal surface. The journals must be smooth and highly polished. The flywheel adds to an engine's smooth running by applying a constant moving force to carry the crankshaft from one firing stroke to the next. The flywheel surface may be used as part of the clutch. ¦ Crankshaft checks include saddle alignment, straightness, clearance, and end play. ¦ Bearings carry the critical loads created by crank shaft movement. Most bearings used today are insert bearings. ¦ Maintaining a specific oil clearance is critical to proper bearing operation. Bearings are available in a variety of undersizes. ¦ Aluminum pistons are light, yet strong enough to withstand combustion pressure. ¦ Piston rings are used to fill the gap between the piston and cylinder wall. Most of today's vehicle engines are fitted with two compression rings and one oil control ring. ¦ When installing a piston and connecting rod assembly, various markings can be used to make sure the installation is correct. Always check the service manual for exact locations. ¦ Connecting rod side clearance determines the amount of oil throw-off from the bearings and measured with a feeler gauge. ¦ The camshaft is supported in the cylinder block by friction-type bearings, or bushings, which are typically pressed into the camshaft bore in the block or head. Camshaft bearings are normally replaced during engine rebuilding. ¦ During most engine rebuilds, a new timing assembly is installed. When installing the timing gears, make sure they are aligned to specifications. ¦ After an engine is rebuilt, a new or rebuilt oil pump is often installed. If the old pump is to be reused, it should be carefully inspected for wear and thoroughly cleaned. QUIZ 1. Name the two most common ways to measure cam lobe wear. 2. What is the deck? 3. What is the name of the component in the lubrication system that prevents excessively high system pressures from occurring as engine speed increases? 4. Where does maximum cylinder bore wear occur? 5. What type of valve lifter automatically compensates for the effects of engine temperature? a. hydraulic b. solid c. roller d. all of the above 6. What is the purpose of compression rings? 7. Most pistons used today are made of: a. cast iron b. aluminum c. ceramic d. none of the above 8. Core plugs: a. are also called expansion plugs b. are used in all cast-iron cylinder blocks c. are a possible source for coolant leaks d. all of the above 9. Which of the following is not of concern when checking a rotor-type oil pump? a. cover flatness b. rotor thickness c. inner rotor-to-outer rotor clearance d. inner rotor-to-pump housing clearance 10. True or False? Oil pressure is determined by whether the pump is a gear type or rotor type and by oil clearances, the pump's pressure regulator valve, and oil viscosity. 11. How is the oil pump driven? 12. Each half of a split bearing is made slightly larger than an exact half. What is this called? a. spread b. crush c. both a and b d. neither a nor b 13. The connecting rod journal is also called the: a. balancer shaft b. vibration damper c. Plastigage d. crankpin 14. What device in the valve train changes rotary motion into reciprocating motion? a. eccentric b. cam c. bushing d. mandrel 15. Which type of oil ring is slotted so that excess oil can pass through it? a. cast iron b. segmented c. both a and b d. neither a nor b ASE-STYLE REVIEW QUESTIONS 1. Technician A uses a feeler gauge and straight edge to determine the pump cover flatness. Technician B uses an outside micrometer to measure the diameter and thickness of the outer rotor. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 2. After installing cam bearings: Technician A checks that the oil holes in the bearings are properly aligned with those in the block by squirting oil into the holes. Technician B checks for proper alignment by inserting a wire through the holes. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 3. Technician A says that a cylinder wall with too smooth a surface will prevent the piston rings from seating properly. Technician B says that a cylinder wall should have a crosshatch honing pattern. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 4. Technician A uses a prybar to stretch the timing chain onto its sprockets. Technician B cools the timing sprockets so that the timing chain will slip over the teeth. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 5. Technician A installs a cup-type core plug with its flanged edge outward. Technician B installs a dish-type core plug with the dished side facing inward. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 6. Technician A uses a micrometer to measure the connecting rod journal for taper. Technician B uses a micrometer to measure the connecting rod journal for out-of-roundness. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 7. Technician A says that piston ring end gaps should be the same for each ring on a piston. Technician B says that piston ring end gaps should be staggered before installing the piston into its bore. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 8. Technician A checks crankshaft end play or end clearance with a feeler gauge. Technician B uses a dial indicator. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 9. When installing an oil pump in an engine: Technician A packs the pump with petroleum jelly. Technician B submerges the pump in clean oil and rotates the pump shaft to fill the pump body. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B 10. Technician A says that counterweights are added to crankshafts to offset the weight of the connecting rods and pistons. Technician B says that the connecting rod bearings are fed a fresh supply of oil through holes drilled in the crankshaft. Who is correct? a. Technician A c. Both A and B b. Technician B d. Neither A nor B === Next: Upper End Theory and Service Prev.: Installing the Oil Pump Home Article Index top of page |
