Mitsubishi K4 overhaul: cylinder head and block step by step
A overhaul of your Mitsubishi K4 — cylinder head off, pistons out, everything measured and properly reassembled — is very doable yourself with the right dimensions and torque values. In this guide you'll find the complete overhaul data for the four-cylinder K4 from the Mitsubishi workshop manual: head gasket selection, head bolt torque and sequence, valve, crankshaft and connecting rod dimensions, and the corresponding torque values.
Suitable for the entire K4 series: K4A, K4B, K4C, K4D, K4E, K4F, K4G, K4M and K4N (four-cylinder diesel). The data below comes from the workshop manual for the direct-injection K4E, K4F, K4G and K4M; for an indirect-injection version, check your engine number and bore.
Disassembling and inspecting the cylinder head
First remove the valve cover, the rocker arm assembly and the pushrods. Loosen the head bolts in the reverse order of the tightening pattern and lift off the head. Check the head for cracks and flatness; if in doubt, have the head surface machined. When overhauling, replace the valve guides, valve stem seals and head gasket as standard. If the head is cracked or the valve area is worn, a new head is often more economical than hours of repair.
Mitsubishi K4 valve data
| Component | Standard value | Service limit |
|---|---|---|
| Valve angle | 45° | — |
| Valve margin (edge) | 1.0 mm | 0.5 mm |
| Valve spring free length (K4E/K4F) | 43 mm | −1.0 mm |
| Valve spring free length (K4M) | 45.5 mm | −1.0 mm |
| Valve spring squareness | ≤ 2° | 3° |
| Valve clearance (cold, intake + exhaust) | 0.25 mm | — |
Selecting the head gasket thickness
The K4 uses a head gasket whose thickness is chosen based on how far the piston protrudes above the top surface of the block (the piston protrusion δ, measured at top dead centre). Measure this for all cylinders and take the largest value. For the K4E, K4F and K4G, the general rule is: the further the piston protrudes, the thicker the gasket. The gaskets can be identified by the number of notches (no notch, one notch or two notches correspond to increasing thickness, roughly 1.41 / 1.53 / 1.6 mm). Choose the correct gasket so the compression ratio is right — the wrong gasket thickness costs compression or lets the piston hit the head.
Cylinder head bolts: torque and sequence
Always use a new head gasket and no liquid gasket sealant. Tighten the head bolts in the numbered sequence from the centre outward, in 2 to 3 progressive steps up to the final torque.
| Version | Bolt | kgf·m | Nm |
|---|---|---|---|
| K4E / K4F | M10 (wet) | 6.5 – 8.0 | 64 – 78 |
| K4E / K4F | M12 (wet) | 11.5 – 12.5 | 113 – 123 |
| K4M | M10 | 10 – 11 | 98 – 108 |
| K4M | M14 | 15 – 16 | 147 – 157 |
Then fit the pushrods and the rocker arm assembly, and adjust the valve clearance to 0.25 mm.
Pistons, connecting rods and bearings
When measuring the bottom end of the engine, pay attention to the piston ring end gap, the connecting rod bearing oil clearance and the crankshaft dimensions. The key standard values:
| Component | K4E / K4F | K4M | Service limit |
|---|---|---|---|
| Piston ring end gap No.1 / No.2 | 0.2 – 0.4 mm | 0.2 – 0.4 mm | 1.5 mm |
| Piston ring end gap, oil ring | 0.3 – 0.45 mm | 0.3 – 0.45 mm | 1.5 mm |
| Connecting rod bearing inner diameter | 42 mm | 48 mm | +0.15 mm |
| Connecting rod bearing oil clearance | 0.025 – 0.080 mm | 0.035 – 0.090 mm | 0.15 mm |
| Crankshaft journal O.D. | 52 mm | 57 mm | −0.15 mm |
| Crankshaft pin O.D. | 42 mm | 48 mm | −0.15 mm |
| Main bearing oil clearance | 0.040 – 0.101 mm | 0.040 – 0.101 mm | 0.15 mm |
| Crankshaft end play | 0.05 – 0.175 mm | 0.05 – 0.205 mm | — |
If you fall outside the service limit on the crankshaft, grind the journals to undersize (0.25 / 0.50 / 0.75 US, with a fillet radius of 2.5 R) and use matching undersize bearing shells. A crankshaft with worn or seized bearings due to oil starvation cannot be reused.
Bottom end torque values
| Component | Version | kgf·m | Nm |
|---|---|---|---|
| Main bearing cap bolt | All | 5.0 – 5.5 | 49 – 54 |
| Connecting rod cap nut | K4E / K4F | 3.2 – 3.5 | 31 – 34 |
| Connecting rod cap nut | K4M | 4.0 – 4.3 | 39 – 42 |
| Flywheel bolt | All | 11.5 – 12.5 | 113 – 123 |
When fitting the crankshaft: note the number and arrow (pointing to the front of the engine) on the main bearing caps, apply sealant to the front and rear cap and to the four side seals, and tighten the caps to 5.0–5.5 kgf·m. Always replace the connecting rod bolts completely during an overhaul — never reuse old bolts.
Everything for your K4 overhaul
- Mitsubishi K4E overhaul kit – direct injection (SKU-850051) — complete: 4 pistons + rings, connecting rod and main bearings, thrust bearing, gasket set and valve guides (76 mm).
- Mitsubishi K4F-DI overhaul kit (SKU-850054) — same setup for the 78 mm K4F.
- Mitsubishi K4C overhaul kit (SKU-850050) — for the 70 mm K4C.
- Individual piston K4E – direct injection, 76 mm (SKU-36002-4) — or the indirect version (SKU-100056).
- Connecting rod bearing / bearing shells K3 / K4 (VAR-0035) — available in standard and oversize.
- Valve seals / valve stem seals K3 / K4 (VAR-410006) — always replace these during a head overhaul.
- Cylinder head Mitsubishi K4E / K4F (SKU-99009) — new, fully cast head.
- Cylinder head + gasket set + glow plugs Mitsubishi K4D (SKU-990027) — complete package for the 87 mm K4D.
- Connecting rod bolt Mitsubishi K4F-DT / K4M / K4N (SKU-780025) — replace the bolts with every overhaul.
Frequently asked questions
What is the head bolt torque for a K4 overhaul?
K4E/K4F: M10 6.5–8.0 kgf·m and M12 11.5–12.5 kgf·m (wet). K4M: M10 10–11 and M14 15–16 kgf·m. In 2–3 steps and in the correct sequence.
Which head gasket do I need?
The correct thickness depends on the piston protrusion. Measure this at top dead centre and choose the gasket with the corresponding number of notches. If in doubt, we can help you using the engine number.
Do I need to replace the connecting rod bolts?
Yes. Always replace the connecting rod bolts completely during an overhaul and tighten them to the specified torque; never reuse old bolts.
