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3.2L 24v - S50B32
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3.2L 24v - S50B32
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Set of 12 trimetal connecting rod half-bearings for BMW inline-six S50B32, European version.
Succeeding the S50B30 in 1995, the S50B32 powers the BMW M3 E36 3.2 and then the Z3 M Roadster and Coupé: a naturally aspirated 3,201 cc inline six with an 86.4 mm bore and a 91 mm stroke, twin overhead camshafts and 24 valves, producing 321 hp. It was built until 2001. This bearing set is specific to the European version: the North American S52B32 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 1 404 008, 009 and 010) and blue (11 24 1 404 791), 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 48.970 / 48.991 mm Housing bore Ø 53.000 / 53.015 mm Width 18 / 18.1 mm | OEM reference Crankpin Ø 48.975 / 48.991 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 6B1497H-STD | ACL Race - Untreated | Standard | 1.993 |
| 6B1497HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.980 |
| 6B1497H-.025 | ACL Race - Untreated | +0.025 | 2.006 |
| 6B1497H-.25 | ACL Race - Untreated | +0.25 | 2.118 |
| CR6853XP | King Racing - Untreated | Standard | 1.991 |
| CR6853XP STDX | King Racing - Untreated | Std, increased clearance (STDX) | 1.978 |
| CR6853XP.026 | King Racing - Untreated | +0.026 | 2.004 |
| CR6853XP0.25 | King Racing - Untreated | +0.25 | 2.118 |
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 | 0.052 to 0.062 mm | 0.049 mm - 0.068 mm |
| Increased clearance (HX / STDX) | Wider clearance: high oil flow, high rpm | 0.077 to 0.087 mm | 0.074 mm - 0.093 mm |
| +0.025 / +0.026 mm | Polished journal | 0.052 to 0.062 mm | 0.049 mm - 0.068 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.052 to 0.062 mm | 0.049 mm - 0.068 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), S50B32 | 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 S50B32 six-cylinder of the M3 E36 and Z3 M, European version:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| BMW | 3 Series (E36) M3 3.2 | S50B32 | 321 hp | 1995–1998 |
| BMW | 3 Series Coupé (E36) M3 3.2 | S50B32 | 321 hp | 1995–1998 |
| BMW | 3 Series Convertible (E36) M3 3.2 | S50B32 | 321 hp | 1996–1999 |
| BMW | Z3 Roadster (E36) M 3.2 | S50B32 | 321 hp | 1997–2000 |
| BMW | Z3 Coupé (E36) M 3.2 | S50B32 | 321 hp | 1998–2001 |
