The 318is engine was designated M42B18 and was derived from the 318i M40 block (made from pearlitic gray cast iron) with siamesed cyliner bores and integral oil jets monuted in big ends 2, 3, 4 & 5 for piston cooling and gudgeon pin lubrication. Big ends bearing are of the three layer type. The complete engine ended up 13kg heavier and 30mm taller than the M40.

The chilled-cast aluminium alloy 16 valve twin cam head is a classic pentroofed design with the spark plug centred between the valves (with a relationship to the M1, M5 and M635CSi engines). The combustion chamber is bi-concave. The top of the rocker cover has a liquid/vapour seperator to reduce oil consumption.

The camshafts have adjustable sprockets, however I am not aware that anyone has improved their engine by changing these. Camshafts have 15mm hollows to reduce inertia and are of short duration but high lift. Valves are sodium cooled and are double sprung.

The throttle body is of the two stage type, 35mm and 54mm respectively. The inlet manifold is in two pieces, its long length improving low down torque. The Throttle Position Sensor potentiometer closed (idle) and open (WOT) positions are self learnt – so no adjustment is necessary. A free flow exhaust header is also fitted.

Technical Info

Designation : M42B18
Torque and Power graphs (standard and after modification) :

Dimensions (nominal) : 84mm/3.31″ bore x 3.19″ stroke
Displacement : 1796 cc
Camshaft : Duration: inlet 252 exhaust 252 Lift: inlet 10.2 exhaust 10.2
Lobe height: 1.8755-1.8803″
Con-rods : Max. weight variance without bearing shells: 4g/14oz split equally between big and small ends
Crankshaft : End play: 0.0031-0.0064″
Thrust on cylinder 4
Cylinders : Max. ovality: 0.01mm/0.0004″
Max. taper: 0.01mm/0.0004″
Cylinder head : Height = 140mm/5.512″; minimum height = 139.55mm/5.494″
Firing order : 1-3-4-2
Fuel Pressure : 43 psi
Oil pressure : 1.3-2.0 Bar/18 psi @ idle, 4.0-4.3 Bar/57-62 psi at 6250rpm
Oil Filter : Hengst E88H D24 in-bowl type
Oil Type : I would recommend a 5W40, 5W50 or 10W50 fully synthetic (the text book says 15W50) as the tappets seem to prefer a lower viscosity oil
Output : 134 (cat) -136 (non-cat) bhp @ 6000rpm; 127 ft-lb @ 4600 rpm
Pistons : Clearance: 0.0004-0.0016″
Piston rings : Gap: Top & bottom compression rings = 0.0080-0.0160″ ; oil ring = 0.0080-0.0180″
Compression pressures : 10-11bar (143-156psi):
Torques : Big ends: Step 1 = 23Nm/17 ft-lbs, Step 2 = +70 degrees
Camshaft sprocket: 13-17 Nm/10-12 ft-lbs
Camshaft bearing cap bolts: 13-17 Nm/10-12 ft-lbs
Crankshaft damper: 300-320 Nm/217-231 ft-lbs
Cylinder head: Step 1 = 30-35Nm/22-25 ft-lbs, Step 2 = +90-95 degrees, Step 3 = +90-95 degrees
Exhaust manifold: 22-24Nm/17-18 ft-lbs
Flywheel: 82-94 ft-lbs
Intake manifold: 13-17Nm/10-12 ft-lbs
Main bearings: Step 1 = 20-25/14-18 ft-lbs, Step 2 = +47-53 degree turn
Viscous fan coupling (LH threads): 40-50Nm/29-36ft-lbs
Timing chain tensioner: 23-27Nm/17-19 ft-lbs
Valves : Seat angle: 45 degrees
Valve stem to guide clearance: 0.020″
Inlet: Solid, stem diameter 6.975mm/0.2756″, head diameter 33mm/1.299″
Exhaust: Sodium filled, diameter 6.975mm/0.2756″, head diameter 30.5mm/1.201″
Seat diameter: inlet = 31.6mm/1.244″, exhaust = 29.1mm/1.146″
Seat width: 1.4-1.9mm/0.055-0.075″
Valve clearance : None, automatically compensated by hydraulic tappets

[source : esatclear.ie]