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Las 15 preguntas de un vistazo

¿Prefieres leer antes de jugar? Abajo están todas las preguntas de la muestra. Las respuestas y explicaciones quedan plegadas hasta que las abras.

1. 1. A compression test shows one cylinder much lower than the rest. A small amount of engine oil is squirted into that cylinder and the test is repeated. The reading comes up close to the others. What does this indicate?

   • A. A burned exhaust valve
   • B. A cracked cylinder head
   • C. Worn piston rings or a worn cylinder wall
   • D. A head gasket leaking between two cylinders
   Ver respuesta y explicación

   Respuesta: C. Worn piston rings or a worn cylinder wall

   The oil temporarily seals the gap between the rings and the bore, so if the reading jumps, the compression was escaping past the rings. If the reading does not change, the leak is somewhere oil cannot seal, which points at a valve, the head gasket or a crack. Adding the oil is what turns a dry compression test into a wet one, and it is the fastest way to split ring problems from valve problems.

2. 2. During a cylinder leakage test, with the cylinder at top dead center on the compression stroke, air is heard hissing from the tailpipe. Which fault does this point to?

   • A. Worn piston rings
   • B. A leaking intake valve
   • C. A leaking head gasket
   • D. A leaking exhaust valve
   Ver respuesta y explicación

   Respuesta: D. A leaking exhaust valve

   A leakage test tells you where the air goes, and each escape route names a part. Out of the tailpipe means the exhaust valve is not sealing. Out of the throttle body or intake means the intake valve. Out of the oil fill or dipstick tube means the rings, because the air reached the crankcase. Bubbles in the radiator or a rising coolant level means the head gasket or a crack. What counts as acceptable leakage varies, so compare against the manufacturer's spec rather than a number you remember.

3. 3. Complete the sentence.

   A cylinder bore is measured with a dial bore gauge just below the ring ridge and again at the bottom of ring travel. The difference between those two readings is the cylinder's _____.

   Opciones para el hueco 1: clearance, out of round, taper, runout

   Ver respuesta y explicación

   Respuesta: taper

   Taper is the change in bore diameter from top to bottom. It forms because the top of the ring travel sees the highest pressure, the most heat and the least lubrication, so the bore wears fastest there. Out of round is a different measurement: two diameters taken at the same depth, ninety degrees apart. Both are checked against spec before you decide whether a block can be honed or has to be bored oversize.

4. 4. Which findings would support a diagnosis of a failed head gasket?

   Marca todas las que correspondan.

   • A. A steady drop in oil pressure that only happens at cold start
   • B. White exhaust smoke with a sweet smell that does not clear once the engine is warm
   • C. A whine from the accessory drive belt that rises with engine speed
   • D. Bubbles rising steadily in the radiator with the cap off and the engine running
   • E. Coolant loss with no external leak anywhere on the engine
   Ver respuesta y explicación

   Respuesta: B. White exhaust smoke with a sweet smell that does not clear once the engine is warm, D. Bubbles rising steadily in the radiator with the cap off and the engine running, E. Coolant loss with no external leak anywhere on the engine

   A failed head gasket lets things cross between passages that should stay separate. Coolant reaching a combustion chamber burns and leaves white steam that smells sweet and keeps coming after warm up, unlike ordinary condensation, which clears. Combustion gas pushed the other way shows as bubbles in the radiator or as pressure in the cooling system. Coolant that disappears with nothing on the ground is the classic internal leak. Belt noise and a cold start oil pressure dip are unrelated systems.

5. 5. An engine puffs blue smoke for a few seconds right after a cold start and again after a long idle at a stoplight, then runs clean. What is the most likely cause?

   • A. Worn valve stem seals or worn valve guides
   • B. Worn main bearings
   • C. A thermostat stuck open
   • D. A restricted air filter
   Ver respuesta y explicación

   Respuesta: A. Worn valve stem seals or worn valve guides

   Blue smoke is burning oil, and the timing tells you how it got into the chamber. While the engine sits or idles, oil seeps down the valve stems past worn seals or loose guides and pools in the port, then burns off in a puff when the engine is started or the throttle opens. Worn rings smoke differently: the smoke is more or less constant and gets worse under load, not just at start up.

6. 6. A technician lays a strip of Plastigage across a rod journal, installs and torques the cap, then removes the cap and compares the crushed width to the scale on the package. What is being measured?

   • A. Crankshaft endplay
   • B. Bearing oil clearance
   • C. Connecting rod side clearance
   • D. Cylinder bore taper
   Ver respuesta y explicación

   Respuesta: B. Bearing oil clearance

   The strip crushes to the width of the gap between the bearing and the journal, so the scale reads oil clearance directly. Do not turn the crankshaft while the strip is in place, because that smears it and ruins the reading. Endplay is measured with a dial indicator while the crank is pried fore and aft, and rod side clearance with a feeler gauge between the rod and the crank cheek. If the crushed strip is noticeably wider at one end, suspect a tapered journal and confirm it with a micrometer.

7. 7. Complete the sentence.

   The radiator cap holds the cooling system under pressure, which raises the coolant's _____. That is why a cap which no longer holds its rated pressure can let an engine boil over even when the temperature gauge looks normal.

   Opciones para el hueco 1: boiling point, freezing point, specific gravity, flow rate

   Ver respuesta y explicación

   Respuesta: boiling point

   Pressure raises the temperature at which a liquid boils, so a sealed system can run hotter without forming steam pockets. The cap also has a second, smaller valve that lets coolant flow back from the recovery tank as the engine cools, and a cap that fails that way collapses hoses instead. Test the cap with a pressure tester and compare it to the rating stamped on it.

8. 8. A vehicle takes far too long to warm up, the temperature gauge stays below normal, and the heater blows cool air on the highway. What is the most likely cause?

   • A. A failed water pump impeller
   • B. A thermostat stuck closed
   • C. A collapsed lower radiator hose
   • D. A thermostat stuck open
   Ver respuesta y explicación

   Respuesta: D. A thermostat stuck open

   The thermostat blocks flow to the radiator until the engine reaches operating temperature. Stuck open, coolant circulates through the radiator all the time, so the engine never gets fully warm and there is little heat left for the heater core. Stuck closed does the opposite and overheats the engine quickly. On most vehicles the engine computer notices a coolant temperature that never reaches the expected range and sets a code, which is a useful confirmation.

9. 9. A compression test finds one cylinder low while all the others read normal. Which of these could produce that result?

   Marca todas las que correspondan.

   • A. A burned or badly seated exhaust valve
   • B. A hole or a crack in that piston
   • C. A clogged fuel injector on that cylinder
   • D. A weak ignition coil on that cylinder
   • E. Valve clearance set too tight, holding a valve slightly open
   Ver respuesta y explicación

   Respuesta: A. A burned or badly seated exhaust valve, B. A hole or a crack in that piston, E. Valve clearance set too tight, holding a valve slightly open

   A compression test is purely mechanical. It asks one question: can this cylinder seal and hold pressure. Anything that leaves a path for the pressure to escape shows up, including a valve that will not seat, a damaged piston and valve lash so tight that the valve never fully closes. Fuel and spark faults cause a misfire with perfectly normal compression, which is exactly why the test is useful for separating the two. Note that a valve held off its seat also cannot dump its heat into the seat, which is how tight lash eventually burns a valve.

10. 10. How is a cylinder head checked for warpage?

    • A. With a precision straightedge and a feeler gauge, checked lengthwise, across the width and along both diagonals
    • B. With a dial bore gauge run along the length of the head
    • C. With an outside micrometer at each corner of the head
    • D. By torquing the head bolts in sequence and watching for movement
    Ver respuesta y explicación

    Respuesta: A. With a precision straightedge and a feeler gauge, checked lengthwise, across the width and along both diagonals

    The straightedge lies on the deck surface and the feeler gauge finds any gap under it. Checking several directions matters because heads rarely warp evenly. An aluminum head that has overheated usually humps in the middle, and that bow only shows up on the lengthwise and diagonal checks. Compare the largest gap you find against the manufacturer's limit to decide between resurfacing and replacement, and check the block deck the same way while the head is off.

11. 11. An engine has a deep knock that is loudest under load and gets noticeably quieter when the ignition or the injector for one cylinder is disabled. What does that point to?

    • A. A sticking hydraulic lifter
    • B. A loose accessory drive pulley
    • C. An exhaust manifold leak
    • D. A worn connecting rod bearing on that cylinder
    Ver respuesta y explicación

    Respuesta: D. A worn connecting rod bearing on that cylinder

    Cutting the cylinder removes the combustion pressure that drives the rod down onto a worn bearing, so the knock softens or disappears. That change is the whole point of the test, because it names the cylinder as well as the fault. Lifter noise is a lighter tap from the top of the engine that does not respond to cutting a cylinder, and an exhaust leak is a tick that is loudest cold and quiets as the metal expands.

12. 12. Complete the sentence.

    Crankshaft endplay is measured with a _____ while the crankshaft is pried back and forth, and piston ring end gap is measured with a _____ after the ring is squared in the bore.

    Opciones para el hueco 1: dial indicator, torque wrench, vacuum gauge, dial bore gauge

    Opciones para el hueco 2: micrometer, feeler gauge, depth gauge, straightedge

    Ver respuesta y explicación

    Respuesta: dial indicator, feeler gauge

    Endplay is the crankshaft's fore and aft movement, controlled by the thrust bearing, and a dial indicator on the end of the crank reads it while you push the crank each way. Ring end gap is the space between the two ends of a ring sitting in the bore, and a feeler gauge slides into that space. Square the ring first by pushing it down with an inverted piston, because a cocked ring gives a false reading. Too little gap and the ring ends butt together as they heat up.

13. 13. An engine with a rubber timing belt is in for belt replacement at the recommended interval. Which practices are correct?

    Marca todas las que correspondan.

    • A. Pry the belt onto the sprockets with a screwdriver so it seats fully
    • B. Line up the camshaft and crankshaft timing marks before the old belt comes off, then confirm them with the new belt installed
    • C. Inspect or replace the tensioner and the idler pulleys while the belt is off
    • D. Turn the engine over by hand through two full crankshaft revolutions and recheck the marks before starting it
    • E. Reuse the old belt if it has no visible cracks
    Ver respuesta y explicación

    Respuesta: B. Line up the camshaft and crankshaft timing marks before the old belt comes off, then confirm them with the new belt installed, C. Inspect or replace the tensioner and the idler pulleys while the belt is off, D. Turn the engine over by hand through two full crankshaft revolutions and recheck the marks before starting it

    On an interference engine a belt that is one tooth off, or a belt that fails, lets a piston hit an open valve, so the marks get verified twice and the engine is turned by hand first. Two crankshaft revolutions equal one camshaft revolution, which is why two turns brings every mark back around. The tensioner and idlers wear on the same clock as the belt and are the usual reason a fresh belt fails early, and many of these engines drive the water pump off the same belt, so it is replaced at the same time. Prying with a screwdriver damages the belt cords, and a belt with no visible cracks can still be at the end of its service life.

14. 14. The oil pressure warning light comes on at idle on a high mileage engine. What should the technician do first?

    • A. Replace the oil pump
    • B. Switch to a much heavier oil viscosity to raise the reading
    • C. Check the oil level and condition, then connect a mechanical gauge to verify the actual pressure
    • D. Replace the main and rod bearings
    Ver respuesta y explicación

    Respuesta: C. Check the oil level and condition, then connect a mechanical gauge to verify the actual pressure

    The warning light is driven by a sender, and a failed sender or its wiring can light the lamp with pressure that is perfectly fine. Verify with a mechanical gauge at the engine speed and temperature the manufacturer specifies before you condemn a part. Low oil level, oil thinned by fuel, a clogged pickup screen, a worn pump and worn bearings all look identical from the dash, and they need different repairs. Switching to a heavier oil raises the number without fixing anything.

15. 15. A vacuum gauge is connected to the intake manifold of an idling engine. The needle drops sharply at regular, repeating intervals and returns each time. What does that pattern suggest?

    • A. A restricted exhaust system
    • B. A leaking or burned valve
    • C. A rich fuel mixture
    • D. A worn oil pump
    Ver respuesta y explicación

    Respuesta: B. A leaking or burned valve

    A regular repeating drop means the same cylinder fails the same way on every cycle, which is what a valve that will not seal looks like. Random, irregular drops point instead at a sticking valve or an intermittent misfire. A reading that is low but steady points at late valve timing or a stretched timing chain, and a reading that starts normal then slowly falls as engine speed is held up is the classic sign of a restricted exhaust. The oil pump has no effect on manifold vacuum.

Qué cubre el ASE A1 de reparación de motor

El A1 es el test de reparación de motor dentro de la serie A de tests de certificación de automóvil que fija el National Institute for Automotive Service Excellence de Estados Unidos. Su esquema de contenidos se parte en cuatro áreas: diagnóstico general del motor, diagnóstico y reparación de la culata y el tren de válvulas, diagnóstico y reparación del bloque motor, y diagnóstico y reparación de los sistemas de lubricación y refrigeración. El diagnóstico general del motor se lleva el mayor número de preguntas de las cuatro, lo que te dice dónde pone el peso el test.

Ese reparto es la parte útil. El A1 no es sobre todo un test de si sabes reconstruir un motor sobre el papel. Es un test de si sabes coger una queja, elegir la prueba correcta y leer bien el resultado. Las pruebas de compresión y de fugas de cilindro, la de presión de aceite, la de presión del sistema de refrigeración, el diagnóstico de ruidos y la medición con regla, micrómetro o comparador salen una y otra vez, porque cada una es un paso de un diagnóstico y no un dato que recitar.

La certificación en sí pide dos cosas. Apruebas el test y documentas dos años de experiencia laboral práctica relevante, aunque la formación relevante puede sustituir una parte. La certificación tampoco dura para siempre. Caduca y vuelves a examinarte para mantenerla vigente. Los plazos de inscripción, lo que cuesta un test y cómo se puntúa los fija la ASE y cambian con el tiempo, así que mira los datos vigentes en la web de la ASE en vez de fiarte de un número que leas en una página de estudio, esta incluida.

Cómo usar esta muestra

Estas 15 preguntas se quedan dentro de la reparación de motor y tiran del razonamiento más que de los nombres. Preguntan qué demuestra una prueba de compresión húmeda que no demuestra una seca, por dónde se va el aire durante una prueba de fugas y qué significa cada vía de escape, qué miden de verdad la conicidad y la ovalización, y por qué un técnico verifica la presión de aceite con un manómetro mecánico antes de tocar una bomba. Ese es el razonamiento que premia el A1.

Hazla de una sentada y sin apuntes, después lee la explicación de cada pregunta, también de las que acertaste. Trata una respuesta fallada como un tema y no como un dato. Si fallaste la pregunta de la prueba de fugas y la de la junta de culata, repasa el sellado de cilindro como una sola materia, porque esas dos son la misma idea vista desde lados distintos.

Combínala con tiempo delante de un motor de verdad. Leer sobre cómo escuadrar un segmento en el cilindro no es lo mismo que hacerlo, y las preguntas de medición del A1 dan por hecho que has tenido las herramientas en la mano. Las muestras hermanas enlazadas abajo cubren la serie A entera y el test A5 de frenos, así que hazlas las tres si vas a por más de una certificación.

Cómo StudyPDF crea tests completos con tu propio material

Quince preguntas te enseñan dónde flojeas. Por sí solas no te preparan, y un banco genérico rara vez coincide con lo que subraya la guía de estudio o el programa de formación que estás usando de verdad.

StudyPDF va por otro camino, parte de tu material. Subes tu guía de estudio de la ASE, tu manual de formación de servicio o los apuntes de tu programa, y Bo, el agente de estudio, crea tests de práctica completos con esas páginas exactas. Cada pregunta sale de tu material y cada explicación cita de dónde viene la respuesta, así que puedes ir directo a la fuente cuando algo no te cuadre. Puedes generar tests nuevos tantas veces como quieras, reducirlos a un área como los sistemas de refrigeración o la medición del bloque y el cigüeñal, y seguir qué conceptos sigues fallando.

No hace falta subir nada para empezar. Si no tienes ningún archivo a mano, di solo un tema, por ejemplo la prueba de fugas de cilindro o el desgaste del tren de válvulas, y Bo escribe un test de práctica sobre eso. Empezar es gratis.