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ACL trimetal connecting rod bearings BMW M10B15 M10B16 M10B18 M10B20
Set of 8 trimetal connecting rod half-bearings for BMW four-cylinder M10.
- Brand and treatment: ACL Race
- Compatibility: 1502 to 2002 (E10), 3 Series (E21, E30), 5 Series (E12, E28)
- Engine codes: M10B15, M10B16, M10B18, M10B20
- Available sizes: standard (STD)
The BMW M10 four-cylinder engine
The M10 is BMW's inline four with a single overhead camshaft and 8 valves, built from 1.5 to 2.0 litres (M10B15, M10B16, M10B18, M10B20), up to the turbocharged version of the 2002 Turbo. It powers the 1500 to 2000 saloons, the 02 (E10), the 3 Series (E21, E30) and the 5 Series (E12, E28). ACL lists the same bearing set for all these displacements: a single set covers the family.
From the factory, BMW fits the M10 with standard production connecting rod bearings, graded by red and blue colour class (part number series 11 24 1 258 428 and 11 24 1 284 550). These bearings are 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
In a trimetal bearing, a steel back carries a copper-lead intermediate layer with high load capacity, itself covered by an anti-friction running layer that spares the crankpin. The set is supplied complete: 8 half shells, i.e. 4 pairs.
Trimetal targets high, sustained loads, whereas aluminium bi-metal is limited to low to medium loads: about 8,000 psi for the latter, up to 12,000 psi for a performance trimetal, 50% more. The benefit shows in strength and durability on turbo, supercharged and high-revving engines.
Technical specifications
| ACL bearings Crankpin Ø 47.975 / 47.991 mm Housing bore Ø 52.000 / 52.010 mm Width 20 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 4B1486H-STD | ACL Race - Untreated | Standard | 1.989 |
Running clearance
Running clearance is the gap between the bearing and the crankpin, filled by the oil film.
While the engine turns, the crankpin floats on this oil film, which carries the load without direct contact with the bearing. Film thickness depends on clearance: too tight, oil passes poorly, temperature rises and the risk of seizure grows; too wide, oil escapes, the film carries less and oil pressure decreases. A correct clearance ensures both sufficient lubrication and a well-maintained film.
| Size / grade | When to choose it | ACL Race Series |
|---|---|---|
| Standard (STD) | Standard journal, not reground | 0.051 to 0.061 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.
Technical guide
These ACL trimetal connecting rod bearings are aimed at built engines and racing: where a standard bearing quickly reaches its limit, they accept more power, more rpm and more boost. The range includes the standard size. It allows the clearance to be tailored to the oil used and the engine's duty.
The brand
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An Australian specialist in high-performance engine bearings since 1949, ACL Bearing Company produces the Race Series: precisely made trimetal bearings, available in numerous sizes and recognised on built engines across the world. |
Vehicle compatibility
This connecting rod bearing set fits the M10 four-cylinder engines of the following BMW models:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| BMW | 1500-2000 (115, 116, 118, 121) 1500 | M10B15 | 80 hp | 1962–1966 |
| BMW | 1500-2000 (115, 116, 118, 121) 1500 / 1600 | M10B16 | 80–97 hp | 1963–1971 |
| BMW | 1500-2000 (115, 116, 118, 121) 1800 / 2000 | M10B18 | 90–103 hp | 1965–1972 |
| BMW | 1500-2000 (115, 116, 118, 121) 2000 / 2000 Ti / Tilux / 2000 Tii | M10B20 | 100–137 hp | 1965–1972 |
| BMW | 1502-2002 (E10) 1502 / 1600 Ti / 1600/2 / 1602 | M10B16 | 75–105 hp | 1967–1977 |
| BMW | 1502-2002 (E10) 1802 | M10B18 | 90–103 hp | 1970–1975 |
| BMW | 1502-2002 (E10) 2002 / 2002 Ti / 2002 Tii / 2002 Turbo | M10B20 | 100–170 hp | 1967–1975 |
| BMW | 1502-2002 Convertible (E10) 1600-2 | M10B16 | 86 hp | 1967–1971 |
| BMW | 1502-2002 Convertible (E10) 2002 | M10B20 | 100 hp | 1971–1975 |
| BMW | 1502-2002 Touring (E6) 1600 | M10B16 | 85 hp | 1971–1973 |
| BMW | 1502-2002 Touring (E6) 1802 | M10B18 | 90 hp | 1971–1975 |
| BMW | 1502-2002 Touring (E6) 2002 / 2002 Tii | M10B20 | 100–130 hp | 1971–1975 |
| BMW | 1600 GT Coupe 1.6 | M10B16 | 105 hp | 1967–1969 |
| BMW | 2000 Coupe (120) C/CA / CS | M10B20 | 101–135 hp | 1965–1970 |
| BMW | 3 (E21) 315 / 316 | M10B16 | 75–90 hp | 1975–1984 |
| BMW | 3 (E21) 316 / 318 / 318 i / 320 i | M10B18 | 90–105 hp | 1975–1983 |
| BMW | 3 (E21) 320 / 320 i | M10B20 | 109–125 hp | 1975–1982 |
| BMW | 3 (E30) 315 | M10B16 | 75 hp | 1982–1991 |
| BMW | 3 (E30) 316 / 316 (Ecotronic) / 316 i / 318 i | M10B18 | 90–105 hp | 1982–1988 |
| BMW | 3 Convertible (E30) 318 Baur TC / 318 i Baur TC | M10B18 | 90–105 hp | 1982–1990 |
| BMW | 5 (E12) 518 / 518 i | M10B18 | 90–102 hp | 1974–1981 |
| BMW | 5 (E12) 520 / 520 i | M10B20 | 115–131 hp | 1972–1979 |
| BMW | 5 (E28) 518 / 518 i | M10B18 | 90–105 hp | 1981–1987 |
Why replace the bearings
Replacing the bearings during a build or rebuild guards against the most expensive failure: a worn-out connecting rod bearing scores the crankpin, contaminates the oil circuit with debris and forces at least a crankshaft regrind, or even a new rod and block. Against such costs a new set weighs little: it is the cheapest part of the rotating assembly, but the one whose failure costs the most.
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Brand
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Reference4B1486H-STD
