Introduction
Available from 2007 to 2013, the BMW S65 was a V8 petrol engine that was derived from BMW’s S85 V10 petrol engine. Replacing BMW’s S54 engine six-cylinder engine, the more common S65B40 variant had a 92.0 mm bore and a 75.2 mm stroke for a capacity of 3998 cc. Reserved for the E92 M3 GTS and E90 M3 CRT, however, the S65B44 extended stroke to 82.0 mm and had a capacity of 4361 cc.
The S65 engine weighed 202 kg.
S65 block and crankcase
Like the S85, the S65 engine had a two-piece Alusil crankcase with a reinforcing bedplate. The bedplate was machined together with the crankcase and, when the engine was assembled, the bedplate was mounted to the upper section of the crankcase. Furthermore, the bedplate assembly contained cast iron bearing bridges to absorb additional forces from the pistons and connecting rods.
The upper low-pressure die-cast crankcase was made from an aluminium-silicon alloy, while the lower crankcase (bedplate) was also produced from die-cast aluminium, though grey cast iron inlays were used to reinforce the bedplate construction. Furthermore, the cylinder bores were formed using exposed hard silicon crystals such that cylinder liners were not required.
The S65 engine had a one-piece crossflow radiator that was used to cool both cylinder banks and wet-sump lubrication with two oil pumps: a primary oil pump and an oil return pump.
Components and internals
The S65 engine had a five-bearing crankshaft that was forged from a single piece (including the two double-chain wheels for driving the valve gear). Furthermore, the S65 engine had:
- high tensile steel connecting rods split by fracture separation. For mass reduction, the upper section of the connecting rod had a trapezoidal shaped cross-section; and,
- aluminium alloy cast pistons with (as per the S85 engine);
S65 cylinder head
The cylinder heads for the S65 engine were produced from a single piece of aluminium alloy. The double overhead camshafts (per cylinder bank) had hollow-cast, one-piece construction with integrated sensor gears, while the variable intake and exhaust camshaft timing (BMW’s double VANOS) operated at normal oil pressure (in contrast to the high pressure operation of the S85 engine).
The inlet camshafts were chain-driven, though the exhaust camshafts were driven by a gearwheel drive. Furthermore, the S65 engine had two double-roller chains between the crankshaft and the inlet camshaft. The four valves per cylinder were actuated by hydraulic bucket tappets.
The S65 engine had a 4-in-1 exhaust manifold in each cylinder bank and the exhaust pipes were manufactured using internal high pressure forming (IHU) at pressures of up to 800 bar. As a result, wall thickness for the seamless stainless steel exhaust pipes was between 0.65 and 1.0 mm.
Injection and ignition
The S65 engine had conventional port injection and operated at a compression ratio of 12.0:1. Unlike the 1-5-4-8-6-3-7-2 cylinder firing order conventionally used for BMW’s V8 engines, the order for the S65 engine was 1-5-4-8-7-2-6-3 and ignition was controlled by the Siemens MSS60 engine management system.
| Engine | Capacity | Peak power | Peak torque | Max. speed | Models | Years |
|---|---|---|---|---|---|---|
| S65B40 | 3998 cc (92.0 x 75.2) |
309kW at 8300rpm | 400Nm at 3900rpm | 8400rpm | E90 M3, E92 M3, E93 M3 |
2008-13 |
| S65B44 | 4361 cc (92.0 x 82.0) |
331kW at 8300rpm | 440Nm at 3750rpm | 8400rpm | E92 M3 GTS | 2010-11 |
| E90 M3 CRT | 2011 |
BMW S65 engine problems
S65: connecting rod bearing wear
The connecting rod bearing clearance to journal ratio for S65 engines produced from 2007 to October 2008 (with 088/089 bearings) is less than is generally recommended by engine builders. This lack of clearance causes inadequate oil lubrication between the crank journal and the connecting rod bearings, resulting in premature wear of the rod bearings. For the 702/703 bearings that were subsequently introduced, bearing eccentricity was increased for greater clearance. After initially specifying 10W60 engine oil, BMW permitted the use of thinner LL-01 approved 0W40, 5W30 and 5W40 oils.
For a detailed discussion of the connecting rod bearing clearance and rod side clearance design attributes, please see http://www.m3post.com/forums/showthread.php?t=892838.
S65: connecting rod side clearance
The S65B40 engine has very little clearance for the connecting clearance for the sides of the connecting rods. If there is insufficient side clearance for the connecting rods, oil cannot escape. As a result extra heat is generated by the friction of the connecting rods colliding against each other. As the engine heats up, the rods will swell and the crankshaft will shrink. Connecting rod side clearance is reduced even further and the connecting rods will start riding against the crankshaft journal fillet. The fillet can be worn down and damaged by this process, and the metal shavings it produces will damage the connecting rod bearings and other engine parts.
S65B40 engine: throttle body actuator failure
For the S65B40 engine, there are two throttle body actuators (part no. 13627838085, one per cylinder bank) that are susceptible to failure. Failure of the throttle body actuator causes the vehicle to enter ‘limp home’ mode and may issue code 2B21 (among others). Throttle body actuator failures have been reported from 50,000 kilometres.
The gears within the actuators are made from plastic and wear over time, causing uneven mesh and increased resistance to motion. As a result, the control board applies additional current to the motor to overcome the resistance. The circuit control board, however, does not have over-current protection so that the driver MOSFETs fail due to source-to-drain shoot-through; this may also cause the gate lead to fail. This, in turn, damages the gate driver circuitry and renders the circuit board inoperable. Since some MOSFET failures do not take out the gate driver, replacing the MOSFETs alone may repair the circuit board.
It is understood that aftermarket suppliers are producing brass gears to retrofit to the actuators.
