- In stock
ACL trimetal connecting rod bearings MINI R50 R52 W10B16
Set of 8 trimetal connecting rod half-bearings for MINI 1.6 16v W10B16.
- Brand and treatment: ACL Race
- Compatibility: MINI Cooper, One (R50, R52)
- Engine codes: W10B16
- Available sizes: standard to +0.25 mm, increased-clearance version (HX)
The MINI W10B16 four-cylinder engine
Fitted to the first-generation MINI Cooper and One (R50 and R52 convertible), the W10B16 is a 1,598 cc inline four with a single overhead camshaft and 16 valves. All its versions share the same crankpin diameter: a single bearing set covers the whole family.
From the factory, this engine is 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.
Trimetal connecting rod bearings
A trimetal bearing combines three layers with complementary roles: a steel back that provides structural strength, a copper-lead intermediate layer that takes the heavy loads and an anti-friction running layer that protects the crankpin. The complete set contains 8 half shells, i.e. 4 pairs.
An aluminium bi-metal bearing, intended for low to medium loads, tops out at around 8,000 psi; a performance trimetal bearing holds up to 12,000 psi, 50% more load capacity. It therefore gains strength and service life on turbocharged, supercharged or high-revving engines.
Technical specifications
| ACL bearings Crankpin Ø 43.992 / 44.008 mm Housing bore Ø 47.000 / 47.020 mm Width 16.25 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 4B2903H-STD | ACL Race - Untreated | Standard | 1.489 |
| 4B2903HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.476 |
| 4B2903H-.025 | ACL Race - Untreated | +0.025 | 1.502 |
| 4B2903H-.25 | ACL Race - Untreated | +0.25 | 1.614 |
Running clearance
Running clearance is the space left between the bearing and the crankpin, permanently filled by the oil film.
With the engine running, the crankpin does not touch the bearing: it rides on this oil film, which takes the load. The clearance sets the film thickness. Too small, it restricts oil flow, raises the temperature and invites seizure; too large, it lets the oil escape, the film loses its load capacity and oil pressure falls. The right clearance combines sufficient lubrication with an oil film that keeps carrying the load.
| Size / grade | When to choose it | ACL Race Series |
|---|---|---|
| Standard (STD) | Standard journal, not reground | 0.048 to 0.057 mm |
| Increased clearance (HX) | Wider clearance: high oil flow, high rpm | 0.074 to 0.082 mm |
| +0.025 mm | Polished journal | 0.048 to 0.057 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.048 to 0.057 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
The ACL connecting rod bearings shown here are trimetal bearings built for engine tuning and racing. They withstand far higher loads than a standard bearing and come in several sizes: the standard size, a +0.025 mm size for a crankpin that has only been polished, a +0.25 mm regrind size and the HX version with increased clearance for high-revving engines or engines needing a high oil flow. This range lets you refit a reground crankshaft without changing product line and match the clearance to the oil and use chosen.
The brand
 |
Founded in Australia in 1949, ACL Bearing Company designs high-performance engine bearings. Its Race Series brings together precision trimetal bearings, offered in a wide choice of sizes and fitted to built engines around the world. |
Vehicle compatibility
This connecting rod bearing set fits the W10B16 four-cylinder of the following MINI models:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| MINI | MINI (R50, R53) Cooper | W10B16 | 116 hp | 2001–2006 |
| MINI | MINI Convertible (R52) Cooper | W10B16 | 116 hp | 2004–2008 |
| MINI | MINI (R50, R53) One | W10B16 | 90 hp | 2001–2006 |
| MINI | MINI Convertible (R52) One | W10B16 | 90 hp | 2004–2007 |
Why replace the bearings
A failing connecting rod bearing does not fail alone: it scores the crankpin, sends debris through the oil circuit and calls at least for a crankshaft regrind, when it does not also take out the rod and the block. On a built engine, a bearing set costs only a fraction of a regrind, and even less of a full rebuild: it is the cheapest part of the rotating assembly and the one whose failure costs the most.
-
Brand
-
Reference4B2903H-STD
