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Autopapyrus · Hyundai Sonata 2.4 GDI G4KJ (2018)
https://autopapyrus.com/guides/hyundai/sonata/complete-engine-overhaul/
Compiled automatically from service literature and owner experience. Specs are for the typical configuration — check them against your exact car before you start.

Hyundai Sonata 2.4 GDI G4KJ (2018): Complete Engine Overhaul

The G4KJ is an aluminum 4-cylinder engine from the Theta II family with direct injection and a timing chain drive. These engines are known for rod bearing oil starvation (metal debris in the crankshaft oil passages), so an overhaul requires thorough flushing of the oil passages and careful inspection of the bearings. This is a difficult job: if you don't have measuring tools and experience, it is best to leave the boring and grinding to specialists.

Difficulty: Hard Time: 3-5 working days (engine removal and installation 8-12 hours, plus inspection, machining and assembly) Steps: 20 Tools: Lift, engine hoist or crane stand, socket and ratchet set, torque wrench (5-250 N·m range), pulley puller, flywheel/drive plate holder, bore gauge and micrometers, Plastigage, seal installer, compression tester, containers for coolant and oil, block sealant.

Part

  • 🔩 G4KJ overhaul kit (2.4 GDI, Theta II): piston rings, main and rod bearings, engine gasket set (head gasket, oil pan gasket, cover gaskets), crankshaft seals, timing chain kit (chain, sprockets, guides, tensioner), oil pump, oil filter, spark plugs, accessory drive belt. Overhaul kit part numbers depend on the size of the undersize bearings and rings
There's a full repair manual for this car Every system, wiring diagrams and torque specs — not just this job. Chilton and 5 more. See manuals →

Step by step

20 steps
  1. Before disassembly, check the condition of the engine: cylinder compression, oil pressure, rod knock, and oil consumption. This will help you decide whether a full overhaul is needed or whether replacing the bearings and rings is enough.
  2. Disconnect the negative battery terminal. Drain the engine oil and coolant. Remove the lower splash shield, the hood (optional, for easier access), the air filter and intake ducts, and the battery and its tray.
  3. Remove the accessories: the A/C compressor (do not open the refrigerant circuit; move it aside), the alternator, and the belt. A power steering pump is not involved (this engine uses electric power steering). Disconnect the fuel rail: first relieve the fuel system pressure and catch any spilled gasoline.
  4. Disconnect the engine wiring harnesses, the injector and sensor connectors, the vacuum hoses, the coolant and heater hoses, and the transmission cable and electrical connectors. Label all connectors and hoses.
  5. Support the engine with a hoist. Disconnect the engine and transmission mounts, then remove the subframe or separate the transmission from the engine (depending on the method you choose). Lift the engine out together with the transmission or separately, and place it on an engine stand. Follow the manufacturer's specification for the exact sequence and mount torque values.
  6. Remove the exhaust manifold with the catalytic converter (it is best to replace the gaskets and studs), the intake manifold, the fuel rail with injectors, and the spark plugs and ignition coils.
  7. Remove the crankshaft pulley, the valve cover, the timing chain from both stages, the sprockets, the tensioner, and the guides. Mark the position of the timing marks before removal. Assess the chain stretch and the wear on the guide shoes.
  8. Remove the cylinder head, loosening the bolts in the reverse of the tightening sequence in 2-3 passes. Inspect the head surface for warpage (the tolerance is usually a few hundredths of a millimeter; use the exact limit from the specification) and check the condition of the valves, guides, and seats.
  9. Turn the block over and remove the oil pan, the oil pump, and the oil pickup, then the rod caps. Mark the caps and pistons by cylinder. Remove the pistons with the connecting rods, then remove the main caps and the crankshaft.
  10. Inspection: measure the cylinders with a bore gauge (taper, out-of-round, wear), the crankshaft journals with a micrometer (main and rod), and the bearing clearances with Plastigage. The nominal cylinder bore is about 88 mm and the piston stroke is about 97 mm. Use the manufacturer's specification for tolerances and undersize bearing sizes. If anything is out of tolerance, the block must be bored and honed and the crankshaft ground by specialists, then oversize pistons and undersize bearings are selected.
  11. Thoroughly clean the block and all the oil passages in the crankshaft and block, and blow them out with compressed air. This is a critical step for this engine: any debris in the passages will quickly destroy the new bearings. Make sure the passages on the rod journals are clean.
  12. Replace the piston rings, and check the ring end gaps (in the cylinder) and the ring grooves in the pistons. Install the rings with the end gaps staggered from one another, lubricate them with engine oil, and use a ring compressor.
  13. Install the crankshaft on new main bearings, lubricated with oil. Tighten the main caps in the correct sequence and in several passes, checking that the shaft turns freely. Use the specification for torque and angle (these engines often use torque-plus-angle tightening). Then install the pistons with connecting rods on new bearings and tighten the rod caps in the same way, per specification.
  14. Install a new oil pump (or check the old one and replace it if worn), the oil pickup, and the oil pan using the sealant the engine is designed for. Allow the sealant to cure for the specified time before filling with oil.
  15. Install the cylinder head with a new gasket and new bolts (the head bolts are torque-to-yield and must not be reused). Tighten in several passes and with the angle turn, strictly following the sequence and values in the specification. Install the camshafts, chain, a new tensioner, and the guides according to the timing marks, and check that the marks line up after two crankshaft revolutions.
  16. Install the valve cover, new crankshaft seals, the pulley, the intake and exhaust manifolds with new gaskets, the fuel rail with injectors (replace the injector O-rings), and the spark plugs and coils.
  17. Install the engine in the reverse order, and reconnect all connectors, hoses, and harnesses. Fit a new oil filter and fill with oil to the manufacturer's specification (usually 5W-20 or 5W-30 per ACEA/API, capacity about 4.5-5 L (4.8-5.3 qt)), and fill with coolant.
  18. Before the first start, crank the engine without starting it (with the fuel supply disabled or the fuel pump fuse removed) until oil pressure appears on the instrument cluster. Then start the engine, let it warm up, and check for leaks, oil pressure, and any unusual noises.
  19. Break-in: for the first 1,000-1,500 km (620-930 miles), avoid hard loads and high rpm, and avoid long periods at a constant speed. Change the oil and filter after 1,000-2,000 km (620-1,240 miles), then follow the normal maintenance schedule.
  20. After assembly, read the codes with a diagnostic scan tool, reset the adaptations, and check the fuel trims and the condition of the catalytic converter.

Common mistakes and warnings

  • The G4KJ engine is sensitive to oil passage cleanliness and oil quality: after the overhaul, use only the recommended oil and change it more often (every 7,000-10,000 km (4,300-6,200 miles)). Take all torque values (cylinder head, main and rod caps, mounts) and clearance tolerances strictly from the manufacturer's specification, as they are critical to engine life. If you have no experience with measuring and assembling engines, leave the boring, grinding, and assembly to a professional engine machine shop. When working on the GDI fuel system (rail pressure up to 150-200 bar (2,200-2,900 psi)), always relieve the pressure and observe fire safety precautions.
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