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Engine topics for the SSW (i) automobile maintenance exam
The engine (エンジン) is one of the two official scope areas. This page sums up the basics at Class 3 mechanic level in plain words and points out where ○× items like to swap things around.
Last updated: 2026-10-10
At a glance
- 4strokes: intake, compression, power, exhaust
- 2crankshaft turns per cycle
- AC→DCalternator output rectified by diodes
- 12Vlead-acid battery with 6 cells
The four-stroke cycle
A four-stroke engine (4サイクル・エンジン) works in the order intake (吸入), compression (圧縮), power (燃焼・膨張) and exhaust (排気). In one cycle the crankshaft turns twice and the camshaft once, opening and closing the intake and exhaust valves. False items often change the order of the strokes or say the camshaft turns at crankshaft speed.
Petrol and diesel
| Petrol | Diesel | |
|---|---|---|
| Ignition | Spark plug (スパーク・プラグ) | Compression ignition, no spark plug |
| Compression ratio | Lower | Higher |
| Exhaust to watch | CO, HC, NOx | NOx and particulate matter (black smoke) |
Knocking (ノッキング) is abnormal combustion heard as a metallic knock. In a petrol engine, overheating or ignition timing that is too advanced makes knocking more likely. When you meet a knocking item, ask: does this make the mixture more or less likely to ignite on its own?
Cooling system
- Water pump (ウォータ・ポンプ) circulates coolant through the engine and radiator.
- Thermostat (サーモスタット) stays closed while the engine is cold so it reaches working temperature quickly, and opens when hot to send coolant to the radiator.
- Radiator cap (ラジエータ・キャップ) has a pressure valve that keeps the system pressurised so the coolant boils less easily. Never open it on a hot engine.
- Coolant (冷却水) is mixed with long-life coolant (LLC) to prevent freezing and rust.
Lubrication system
The oil pump sends oil through the oil filter to every friction point. Engine oil does more than lubricate: it also cools, seals (between the piston rings and the cylinder), cleans and protects against rust. ○× items often say oil "only lubricates" to make a false statement.
Battery, alternator and starter
A typical car battery is a 12V lead-acid battery with 6 cells of about 2V each. The electrolyte is dilute sulphuric acid, and its specific gravity falls as the battery discharges. Charging gives off hydrogen, so keep flames away. When removing cables, disconnect the negative terminal first; when fitting, connect it last.
The alternator (オルタネータ) makes alternating current that diodes rectify into direct current, and a regulator keeps the voltage steady. The starter (スタータ) is a DC motor that turns the crankshaft to start the engine.
Continue with chassis and brakes and measuring tools, and practise with the mock exams.
Sources checked: the JASPA specified skills test page (2024 test summary), the MLIT implementation rules and acceptance handbook (MLIT page) and the Prometric booking page. Rules can change, so check the latest version at these sources.
FAQ
How many crankshaft turns does one four-stroke cycle take?
Two. The crankshaft turns twice for intake, compression, power and exhaust; the camshaft turns at half crankshaft speed.
What is the difference between the thermostat and the radiator cap?
The thermostat closes the coolant path while the engine is cold so it warms up quickly. The radiator cap holds pressure in the system so the coolant boils less easily.
What current does a car alternator make?
The alternator (オルタネータ) produces alternating current, which diodes rectify into direct current to charge the battery.
Does a diesel engine have spark plugs?
No spark plugs for ignition. The fuel ignites by itself when it is injected into air that compression has made very hot.
Take a mock exam and see right away which items you missed and why.
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