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2.0L 8v - M10B20 with 121 series cylinder head
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2.0L 8v - M10B20 with 121 series cylinder head
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Set of 8 trimetal connecting rod half-bearings for BMW four-cylinder M10.
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.
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 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 |
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 |
|---|---|---|
| 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.
The ACL 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. |
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 |
