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2.3L 16v - S14B23
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2.3L 16v - S14B23
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Set of 8 trimetal connecting rod half-bearings for the BMW S14 inline-four.
An inline four with twin overhead camshafts and 16 valves, the S14 powers the BMW M3 of the E30 3 Series from 1986, as well as the 320is. It comes in three displacements: the 1,990 cc S14B20, the 2,302 cc S14B23 and the 2,467 cc S14B25, reserved for the M3 Evolution II. All three share the same crankpin diameter: a single bearing set covers the whole family.
From the factory, BMW fits the S14 with standard production connecting rod bearings, supplied as half shells graded by colour class (part numbers 11 24 1 310 515 red and 11 24 1 310 518 yellow). These bearings are sized for the loads of the original engine: as soon as power, engine speed or compression 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 8 half shells, four pairs for a four-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 47.975 / 47.991 mm Housing bore Ø 52.000 / 52.015 mm Width 20 mm | OEM reference Part no. 11 24 1 310 515 (red) and 11 24 1 310 518 (yellow) |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 4B1568H-STD | ACL Race - Untreated | Standard | 1.993 |
| 4B1568HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.980 |
| 4B1568H-.025 | ACL Race - Untreated | +0.025 | 2.006 |
| 4B1568H-.25 | ACL Race - Untreated | +0.25 | 2.118 |
| CR4596XP | King Racing - Untreated | Standard | 1.994 |
| CR4596XP.026 | King Racing - Untreated | +0.026 | 2.007 |
| CR4596XP0.25 | King Racing - Untreated | +0.25 | 2.121 |
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 | 0.051 to 0.061 mm | 0.048 mm - 0.055 mm |
| Increased clearance (HX) | Wider clearance: high oil flow, high rpm | 0.077 to 0.086 mm | |
| +0.025 / +0.026 mm | Polished journal | 0.051 to 0.061 mm | 0.048 mm - 0.055 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.051 to 0.061 mm | 0.048 mm - 0.055 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) |
| 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, +0.026 and +0.25 mm |
This connecting rod bearing set fits the S14 four-cylinder (S14B20, S14B23 and S14B25) of the following BMW models:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| BMW | 3 Series (E30) 320is | S14B20 | 192 hp | 1988–1990 |
| BMW | 3 Series (E30) M3 2.3 | S14B23 | 195–215 hp | 1986–1991 |
| BMW | 3 Series (E30) M3 EVO I 2.3 | S14B23 | 220 hp | 1988–1990 |
| BMW | 3 Series Convertible (E30) M3 2.3 | S14B23 | 195–215 hp | 1988–1993 |
| BMW | 3 Series (E30) M3 EVO II 2.5 | S14B25 | 238 hp | 1990–1992 |
