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Class 3 gasoline engine (3級ガソリン・エンジン) exam topics

3級ガソリン・エンジン has the most candidates of the three types. It covers the construction and operation of the four-stroke petrol engine, its support systems and the engine electrics.

Last updated: 2026-10-19

The four-stroke cycle

Four strokes: intake (吸入きゅうにゅう), compression (圧縮あっしゅく), power (燃焼ねんしょう・膨張ぼうちょう) and exhaust (排気はいき). One cycle takes two crankshaft revolutions while the camshaft turns once. Items often ask which valve is open on which stroke, and why valves open early and close late.

Main parts

Part	Japanese	Often asked
Block and head	シリンダ・ブロック, シリンダ・ヘッド	Head gasket, flatness of the head face
Piston and rod	ピストン, コンロッド	Compression and oil rings, piston clearance
Crankshaft	クランクシャフト	Firing order, oil clearance with プラスチ・ゲージ
Valves	バルブ, カムシャフト	Valve clearance, timing belt, timing chain
Lubrication	潤滑装置じゅんかつそうち	Oil pump, filter, relief valve, viscosity grades
Cooling	冷却装置れいきゃくそうち	Radiator, thermostat, pressure cap, coolant
Fuel	電子制御式燃料噴射装置でんしせいぎょしきねんりょうふんしゃそうち	Injectors, sensors, fuel pump
Ignition	点火装置てんかそうち	Spark plugs, plug gap, ignition timing, ignition coil
Starting and charging	スタータ, オルタネータ	Starter motor, alternator, rectifier diodes, regulator
Battery	バッテリ	Electrolyte specific gravity, Ah capacity, charging

Exhaust emissions

The three main pollutants are CO, HC and NOx. A three-way catalyst (三元触媒さんげんしょくばい) reduces all three when the mixture is close to the stoichiometric ratio, and the O2 sensor helps the ECU keep it there. Items often ask which pollutant rises with a rich or a lean mixture.

Common confusions

The thermostat is closed while the coolant is cold and opens when it is hot, so the engine warms up quickly.
"Hot" and "cold" spark plugs: a cold plug sheds heat better and suits engines under heavy load.
The alternator produces alternating current; rectifier diodes turn it into direct current to charge the battery.

Practise gasoline papers

The app has 20 Class 3 gasoline engine papers, papers 1–3 free, with switchable furigana and a translation for every item. For the related formulas see Class 3 calculations.

VIP unlocks papers 4 to 20 in all three subjects (51 papers), the per-item tips and the detailed explanations for missed items. VIP is bought inside the iOS app with Apple payment, and Apple shows the price. The App Store version is coming soon. You can try the free exams on the web now.

Sources checked on 2026-10-19: the JASPA registration test page and its 2026 (令和8) guide, the JASPA results for the 2025 first session, the JASPA past papers page and the MLIT press release on the new mechanic qualifications. Rules can change, so check the latest version at these sources.

FAQ

Are there many electrical items in the gasoline paper?

Yes. Ignition, the starter, the alternator and the battery are important parts of the Class 3 gasoline engine textbook.

Do I need formulas?

A few: total displacement, compression ratio, Ohm's law and electrical power. See the Class 3 calculations page to practise.

How many people sit Class 3 gasoline?

According to JASPA's 2025 first-session results, 3,831 people sat the Class 3 gasoline written test and 2,650 passed (69.2%).

Take a 30-item mock paper and see right away which items you missed and why.

Try it free now

Papers 1–3 of every subject are free, with furigana. Opens in your browser, no sign-up.