Mitsubishi S3L & S4L Overhaul: Cylinder Head and Block
Mitsubishi S3L & S4L Overhaul: Cylinder Head and Block
Are you overhauling a Mitsubishi S3L or S4L? Then the result stands or falls with the correct wear limits and torque settings. Below you'll find the key measurements and clearances for the cylinder head, block, pistons, and crankshaft — straight from the workshop service manual — plus the torque specifications and head bolt tightening sequence you'll need for reassembly.
Suitable for the entire series: Mitsubishi S3L, S3L2, S4L, and S4L2. Note: the S3L2/S4L2 have a longer stroke (92 mm) than the S3L/S4L (78.5 mm), so pistons and various gaskets differ per type.
Mitsubishi S3L & S4L Cylinder Head Overhaul
Flatness is crucial on the swirl chamber head. The allowable distortion of the bottom surface is 0.05 mm or less; up to 0.10 mm you can have the surface resurfaced, above that it must be replaced. The same applies to the top surface of the block (0.05 mm standard, resurface up to 0.10 mm).
| Component | Standard | Limit | Action |
|---|---|---|---|
| Head bottom surface distortion | 0.05 mm or less | 0.10 mm | Resurface / replace |
| Block top surface distortion | 0.05 mm or less | 0.10 mm | Resurface / replace |
| Intake/exhaust manifold surface flatness | — | 0.15 mm | Resurface / replace |
| Push rod deflection | — | 0.3 mm | Replace |
Mitsubishi S3L & S4L Cylinders, Pistons, and Piston Rings
The standard cylinder bore is 78.0 mm (+0.03); at a bore of 78.2 mm or more (or excessive out-of-roundness), reboring or replacement is needed. Corresponding oversizes are 0.25 and 0.50 OS.
| Measurement / Clearance | Standard | Limit |
|---|---|---|
| Cylinder bore | 78.0 mm (+0.03) | 78.2 mm |
| Piston-to-cylinder clearance | 0.035–0.086 mm | 0.300 mm |
| Piston pin-to-boss clearance | 0.006–0.018 mm | 0.050 mm |
| 1st compression ring end gap | 0.15–0.30 mm | 1.50 mm |
| 2nd compression ring end gap | 0.15–0.35 mm | 1.50 mm |
| Oil ring end gap | 0.20–0.40 mm | 1.50 mm |
| Max. piston weight difference | ± 5 g | — |
Mitsubishi S3L & S4L Crankshaft, Connecting Rods, and Bearings
| Measurement / Clearance | Standard | Limit |
|---|---|---|
| Crankshaft main journal diameter | 51.985–52.000 mm | — |
| Crankshaft crank pin diameter | 47.950–47.964 mm | — |
| Main bearing oil clearance | 0.030–0.077 mm | 0.100 mm |
| Connecting rod bearing oil clearance | 0.025–0.072 mm | 0.150 mm |
| Crankshaft end play | 0.050–0.175 mm | 0.500 mm |
| Connecting rod end play | 0.10–0.35 mm | 0.50 mm |
| Crankshaft bend | 0.025 mm | 0.050 mm |
Mitsubishi S3L & S4L Torque Specifications for Reassembly
| Component | N·m | kgf·m |
|---|---|---|
| Cylinder head bolt | 83.4–93.2 | 8.5–9.5 |
| Main bearing cap bolt | 49.0–53.9 | 5.0–5.5 |
| Connecting rod cap nut | 32.4–37.3 | 3.3–3.8 |
| Flywheel bolt | 127–137 | 13.0–14.0 |
| Crankshaft pulley nut | 147–196 | 15.0–20.0 |
| Rocker arm support bolt | 9.81–19.6 | 1.0–2.0 |
Installing the Cylinder Head and Tightening the Head Bolts
- Make sure the top surface of the block and the piston crowns are clean. Do not use liquid gasket under the head gasket.
- Insert two guide pins (M10×1.25) into the bolt holes, lay the head gasket over the pins, and place the head.
- Remove the guide pins, insert the head bolts, and tighten them in a few stages in the correct sequence.
- Final torque: 83.4–93.2 N·m. Sequence — S3L/S3L2: top 8-4-2-7, middle 6-1-3-5, bottom 10-9-11. S4L/S4L2: top 10-4-2-5-7, middle 8-6-1-3-9, bottom 14-12-11-13 (front of engine on the left).
- Assemble the rocker arm, set the valve clearance to 0.25 mm (cold), and re-check this after break-in.
Overhaul parts in stock: complete S4L/S4L2 overhaul kit (VAR-0032) or S3L/S3L2 (VAR-0018), individual S4L cylinder head (VAR-0172) or S3L (VAR-0157), piston (VAR-0028), piston rings (VAR-0022), connecting rod bearing (VAR-0023) and cylinder liner (SKU-11111127). Main bearings are included in the overhaul kit.
Also useful during the overhaul: connecting rod (VAR-0170), head bolts (SKU-780007), intake valve (SKU-97015) and exhaust valve (SKU-97016), valve guides, valve springs (SKU-97077), valve stem seals (VAR-410006) and the crankshaft oil seal (SKU-96085).
Frequently Asked Questions
When should I rebore the cylinders?
When the bore has increased to 78.2 mm or more, or in case of excessive out-of-roundness. Oversizes of 0.25 and 0.50 mm are available.
What is the maximum oil clearance for the main bearings?
Standard is 0.030–0.077 mm; at 0.100 mm or more, replace the main bearings.
Are pistons from an S4L and S4L2 interchangeable?
No. The S4L2 has a longer stroke than the S4L, so pistons and various gaskets differ. Always order based on the exact engine type.
