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1.8L 16v - BP
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1.8L 16v - BP
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Set of 8 trimetal connecting rod half-bearings for Mazda 323 and MX-5 (B6, BP, ZM).
The B6 (1.6 litre), BP (1.8 litre) and ZM (1.6 litre) are Mazda inline four-cylinder engines, fitted notably to the 323 and the MX-5, in naturally aspirated and turbocharged versions (B6T, BP Turbo). ACL and King list the same bearing set for all these versions: a single set covers the family.
From the factory, these engines are fitted with standard production connecting rod 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 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 44.940 / 44.956 mm Housing bore Ø 48.000 / 48.016 mm Width 17 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 4B8351H-STD | ACL Race - Untreated | Standard | 1.515 |
| 4B8351HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.502 |
| 4B8351H-.025 | ACL Race - Untreated | +0.025 | 1.528 |
| 4B8351H-.25 | ACL Race - Untreated | +0.25 | 1.640 |
| 4B8351H-.50 | ACL Race - Untreated | +0.50 | 1.765 |
| CR4002XP | King Racing - Untreated | Standard | 1.509 |
| CR4002XP STDX | King Racing - Untreated | Std, increased clearance (STDX) | 1.496 |
| CR4002XP.026 | King Racing - Untreated | +0.026 | 1.522 |
| CR4002XP0.25 | King Racing - Untreated | +0.25 | 1.636 |
| CR4002XP0.5 | King Racing - Untreated | +0.50 | 1.763 |
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 | 0.049 to 0.058 mm | 0.045 mm - 0.048 mm |
| Increased clearance (HX / STDX) | Wider clearance: high oil flow, high rpm | 0.074 to 0.083 mm | 0.070 mm - 0.073 mm |
| +0.025 / +0.026 mm | Polished journal | 0.049 to 0.058 mm | 0.045 mm - 0.048 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.049 to 0.058 mm | 0.045 mm - 0.048 mm |
| +0.50 mm | Journal reground to 0.50 mm | 0.049 to 0.058 mm | 0.045 mm - 0.048 mm |
Checking on assembly: lay a calibrated strip (Plastigauge) on the journal, torque the rod cap to spec, then compare the crushed strip against the gauge to read the clearance.
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 +0.50 mm (+ increased clearance HX) | Standard to +0.50 mm (+ increased clearance STDX) |
This connecting rod bearing set fits the B6, BP and ZM four-cylinder engines of the following Mazda models:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| Mazda | 323 III Hatchback (BF) 1.6 GT (BF106) / 1.6 GT Turbo 4WD (BF2) / 1.6 GT Turbo (BF1) / 1.6 4WD (BFMR) | B6, B6T | 86–140 hp | 1985–1993 |
| Mazda | 323 III Saloon (BF) 1.6 GT (BFMP) / 1.6 GT Turbo (BFMP) / 1.6 Turbo | B6, B6T | 85–140 hp | 1985–1991 |
| Mazda | 323 III Station Wagon (BW) 1.6 (BW106) | B6 | 86 hp | 1986–1995 |
| Mazda | 323 F IV (BG) 1.6 16V (BG6S, BG6P) / 1.8 16V (BG8S, BG8P) / 1.8 16V GT (BG8S, BG8P) / 1.6 | B6, BP, B6T | 88–140 hp | 1987–1994 |
| Mazda | 323 C IV (BG) 1.6 16V (BG6Z) / 1.8 16V GT (BG8S) / 1.8 16V Turbo 4WD (BG8S) / 1.8 16V 4WD (BG8S) | B6, BP, BP Turbo | 88–185 hp | 1989–1994 |
| Mazda | 323 S IV (BG) 1.6 16V (BG6S) / 1.8 16V Turbo 4WD (BG8R) / 1.8 16V GT (BG8P) | B6, BP Turbo, BP | 88–163 hp | 1989–1996 |
| Mazda | MX-5 I (NA) 1.8 (NA8C) / 1.8 | BP, BP-ZE | 130–135 hp | 1993–1998 |
| Mazda | RUSTLER 1.6 | B6 | 105 hp | 1993–2004 |
| Mazda | 323 C V (BA) 1.8 / 1.8 16V (BA8P) | BP, BP-ZE | 114–125 hp | 1994–1998 |
| Mazda | 323 F V (BA) 1.8 16V (BA8P) / 1.8 16V | BP-ZE, BP | 114–135 hp | 1994–1998 |
| Mazda | 323 S V (BA) 1.8 16V (BA11) / 1.8 (BA11) | BP-ZE, BP | 114–125 hp | 1994–1998 |
| Mazda | MX-5 II (NB) 1.8 16V (NB8C) / 1.8 i Turbo / 1.8 i (NB8C) / 1.8 | BP-ZE, BP Turbo, BP4W, BPD | 141–185 hp | 1998–2005 |
| Mazda | 323 S VI Saloon (BJ) 1.6 (BJ12) / 1.6 (BJ10M) / 1.6 (BJ10M, BJ12) | ZM | 95–106 hp | 1998–2004 |
| Mazda | 323 F VI Hatchback (BJ) 1.6 (BJ10M) | ZM | 95–98 hp | 2001–2004 |
| Mazda | MX-3 (EC) 1.6 i | B6D | 107 hp | 1993–1998 |
| Mazda | 323 III Hatchback (BF) 1.6 GT Turbo 4WD (BF2) | B6F | 150 hp | 1987–1989 |
| Mazda | 323 F V (BA) 1.6 | B6D | 109 hp | 1994–1998 |
| Mazda | 323 S V (BA) 1.6 AWD / 1.6 (BA11) | B6D | 109–116 hp | 1994–1998 |
