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3.0L 24v - S50B30
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3.0L 24v - S50B30
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Set of 12 trimetal connecting rod half-bearings for BMW inline-six S50B30, European version.
Launched in 1992 in the BMW M3 E36, the S50B30 is a naturally aspirated 2,990 cc inline six with an 86 mm bore and an 85.8 mm stroke, twin overhead camshafts and 24 valves. It produces 286 hp, up to 295 hp depending on the version, until 1995, when the S50B32 took over. This bearing set is specific to the European version: the North American S50B30 uses different connecting rod bearings.
From the factory, BMW fits this engine with connecting rod bearings graded by colour class, red (part numbers 11 24 1 404 133, 134 and 135) and blue (11 24 1 404 688), selected according to the machining tolerances of the crankpin. These are standard production bearings, sized for the loads of the original engine: as soon as power, engine speed or boost pressure increase, they reach their limits.
A trimetal bearing stacks three layers: a steel back, a copper-lead intermediate layer with high load capacity and an anti-friction running surface that protects the journal. The complete set contains 12 half shells, six pairs for a six-cylinder engine.
The original bearing relies on an aluminium alloy over a steel back, intended for low to medium loads, whereas trimetal is designed for high, sustained loads: an aluminium bi-metal takes around 8,000 psi, a performance trimetal up to 12,000 psi, 50% more. Hence better resistance and better durability on turbocharged, supercharged and high-revving engines.
| ACL / King bearings Crankpin Ø 49.970 / 49.991 mm Housing bore Ø 53.000 / 53.020 mm Width 18 / 18.1 mm | OEM reference Crankpin Ø 49.975 / 49.991 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 6B1515H-STD | ACL Race - Untreated | Standard | 1.493 |
| 6B1515HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.480 |
| 6B1515H-.025 | ACL Race - Untreated | +0.025 | 1.506 |
| 6B1515H-.25 | ACL Race - Untreated | +0.25 | 1.618 |
| CR6854XP | King Racing - Untreated | Standard | 1.491 |
| CR6854XP STDX | King Racing - Untreated | Std, increased clearance (STDX) | 1.478 |
| CR6854XP.026 | King Racing - Untreated | +0.026 | 1.504 |
| CR6854XP0.25 | King Racing - Untreated | +0.25 | 1.618 |
The running clearance is the gap between the bearing and the journal where the oil film flows.
In operation, the crankshaft journal does not rub against the bearing: it rides on this oil film, which carries the load. Clearance sets the thickness of this film: too tight, oil flows poorly, temperature rises and the risk of seizure increases; too loose, oil escapes, the film loses load-carrying capacity and oil pressure drops. The right clearance is the balance between adequate lubrication and a well-maintained oil film.
| Size / grade | When to choose it | ACL Race Series | King XP |
|---|---|---|---|
| Standard (STD) | Standard journal, not reground | 0.053 to 0.063 mm | 0.050 mm - 0.070 mm |
| Increased clearance (HX / STDX) | Wider clearance: high oil flow, high rpm | 0.078 to 0.088 mm | 0.075 mm - 0.095 mm |
| +0.025 / +0.026 mm | Polished journal | 0.053 to 0.063 mm | 0.050 mm - 0.070 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.053 to 0.063 mm | 0.050 mm - 0.070 mm |
Checking on assembly: lay a calibrated strip (Plastigauge) on the journal, torque the rod cap to spec (see the torque table below), then compare the crushed strip against the gauge to read the clearance.
| Bolts | By torque | By stretch (gauge) |
| Original bolts (OEM), S50B30 | 5 Nm + 20 Nm + 65° | |
| Forged rod, ARP2000 (3/8″ × 38 mm) | 61 Nm | 0.140 to 0.152 mm |
| Forged rod, ARP L19 (3/8″ × 38 mm) | 67.8 Nm | 0.152 to 0.165 mm |
ARP recommends the stretch method (gauge).
The ACL and King rod bearings shown here are trimetal bearings, designed for engine building and racing. Compared with an original bearing, they handle far higher loads: they cope with increased power, high rpm or the addition of a turbo or supercharger, where a standard bearing quickly reaches its limit.
 | ACL Bearing Company, an Australian manufacturer of high-performance engine bearings since 1949, offers with its Race Series precise trimetal bearings, available in many sizes and proven on built engines worldwide. |
 | King Engine Bearings, an Israeli manufacturer of high-performance engine bearings since the 1960s, offers with its pMax Black trimetal alloy bearings designed for heavy loads. |
| Criterion | ACL Race Series | King Racing |
| Cross-section |  |  |
| Type | High-performance trimetal bearing | High-performance trimetal bearing |
| Country of manufacture | Australia | Israel |
| Construction | Trimetal: steel back, copper layer, soft surface | Trimetal: steel back, copper layer, soft surface |
| Alloy | Race Series (copper-lead) | pMax Black (hardened copper-lead) |
| Protective coating | No | No |
| Available sizes | Standard to +0.25 mm (+ increased clearance HX) | Standard to +0.25 mm (+ increased clearance STDX) |
This connecting rod bearing set fits the BMW S50B30 six-cylinder of the M3 E36, European version:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| BMW | 3 Series (E36) M3 3.0 | S50B30 | 286 hp | 1994–1995 |
| BMW | 3 Series Coupé (E36) M3 3.0 | S50B30 | 286–295 hp | 1992–1995 |
| BMW | 3 Series Convertible (E36) M3 3.0 | S50B30 | 286 hp | 1994–1995 |
