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Trimetal connecting rod bearings BMW M5 E39 Z8 S62B50
Set of 16 trimetal connecting rod half-bearings for BMW V8 S62B50.
- Brands and treatments: ACL Race and King Racing
- Compatibility: M5 E39, Z8 Roadster
- Engine codes: S62B50
- Available sizes: standard to +0.25 mm, increased-clearance versions (HX, STDX)
The BMW S62B50 V8 engine
Fitted to the BMW M5 E39 from 1998 and then to the Z8 roadster, the S62B50 is a naturally aspirated 4,941 cc V8 with a 94 mm bore, an 89 mm stroke and 32 valves, producing 400 hp. It was built until 2003.
From the factory, BMW fits this engine with connecting rod bearings graded by colour class (part numbers 11 24 1 407 492, 493, 541 and 542), 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.
Trimetal connecting rod bearings
Three layers make up a trimetal bearing: the steel back for stiffness, the copper-lead intermediate layer for load capacity, then the anti-friction running layer that protects the crankpin. This set includes 16 half shells, that is 8 pairs.
Where an aluminium bi-metal bearing, designed for low to medium loads, withstands about 8,000 psi, a performance trimetal bearing goes up to 12,000 psi: 50% extra margin. That is what keeps it durable on an engine boosted by a turbo or supercharger, or pushed to high rpm.
Technical specifications
| ACL / King bearings Crankpin Ø 48.970 / 48.991 mm Housing bore Ø 53.000 / 53.013 mm Width 16.9 / 17 mm |
OEM reference Crankpin Ø 48.975 / 48.991 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 8B1591H-STD | ACL Race - Untreated | Standard | 1.993 |
| 8B1591HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.980 |
| 8B1591H-.025 | ACL Race - Untreated | +0.025 | 2.006 |
| 8B1591H-.25 | ACL Race - Untreated | +0.25 | 2.118 |
| CR8063XP | King Racing - Untreated | Standard | 1.991 |
| CR8063XP STDX | King Racing - Untreated | Std, increased clearance (STDX) | 1.978 |
| CR8063XP.026 | King Racing - Untreated | +0.026 | 2.004 |
| CR8063XP0.25 | King Racing - Untreated | +0.25 | 2.118 |
Running clearance
Between the crankpin and the bearing there is a small gap, the running clearance, in which the oil film circulates.
In operation there is no metal-to-metal contact: the crankpin turns on this oil film, which supports the whole load. The clearance determines its thickness. A clearance that is too tight hinders oil flow, heats the assembly and promotes seizure; one that is too wide lets oil leak away, weakens the film and makes oil pressure drop. The correct clearance balances oil flow and film strength.
| 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 - 0.067 mm |
| Increased clearance (HX / STDX) | Wider clearance: high oil flow, high rpm | 0.077 to 0.087 mm | 0.074 mm - 0.092 mm |
| +0.025 / +0.026 mm | Polished journal | 0.052 to 0.062 mm | 0.049 mm - 0.067 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.052 to 0.062 mm | 0.049 mm - 0.067 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.
Connecting rod bolt torques
| Bolts | By torque | By stretch (gauge) |
| Original bolts (OEM), S62B50 | 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).
Technical guide
Designed for engine building and motorsport, these ACL and King trimetal connecting rod bearings carry much more load than an original bearing, whether the engine gains power, revs higher or receives a turbo or supercharger. They are available in several sizes: the standard size, a +0.025 / +0.026 mm size for a crankpin that has only been polished, a +0.25 mm regrind size and the HX / STDX version with increased clearance for high-revving engines or engines needing a high oil flow. That makes it possible to put a reground crankshaft back into service without changing range and to set the clearance for the oil and use.
The two brands
 |
ACL Bearing Company has been making high-performance engine bearings in Australia since 1949. Its Race Series offers precise trimetal bearings, available in many sizes and proven in tuned and racing engines worldwide. |
 |
King Engine Bearings, an Israeli manufacturer active since the 1960s, produces high-performance engine bearings. Its pMax Black trimetal alloy is designed to withstand heavy loads. |
Construction and advantages
| 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) |
Vehicle compatibility
This connecting rod bearing set fits the BMW S62B50 V8 of the M5 E39 and Z8:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| BMW | 5 Series (E39) M5 | S62B50 | 400 hp | 1998–2003 |
| BMW | Z8 Roadster (E52) 4.9 | S62B50 | 400 hp | 2000–2003 |
Why replace the bearings
When a connecting rod bearing gives way, the damage quickly spreads beyond the part itself: a scored crankpin, debris carried through the whole oil circuit, a crankshaft to regrind at the very least, sometimes a rod and block lost. A bearing set costs far less than a regrind and is nothing compared with a complete engine rebuild. It is the cheapest part of the rotating assembly, yet the one whose failure is most expensive.
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Brand
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Reference8B1591H-STD
