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ACL trimetal connecting rod bearings BMW N52B25 N52B30 N53B25 N53B30
Set of 12 trimetal connecting rod half-bearings for BMW inline six N52 and N53.
- Brand and treatment: ACL Race
- Compatibility: 1, 3, 5, 6, 7 Series, X1, X3, X5, Z4
- Engine codes: N52B25, N52B30, N53B25, N53B30
- Available sizes: standard to +0.50 mm, increased-clearance version (HX)
The BMW N52 and N53 six-cylinder engines
The N52 is BMW's naturally aspirated inline six with twin overhead camshafts and 24 valves, in 2.5-litre (N52B25) and 3.0-litre (N52B30) form; the N53 (N53B25, N53B30) is its direct-injection development. They power the 1, 3, 5, 6 and 7 Series, the X1, X3, X5 and the Z4. Same crankpin diameter: a single bearing set covers the whole family.
From the factory, BMW fits the N52 with standard production connecting rod bearings, graded by colour class (part numbers 11 24 7 628 035 blue and 11 24 7 628 034 red). 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
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 12 half shells, i.e. 6 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 49.973 / 49.993 mm Housing bore Ø 53.600 / 53.616 mm Width 17.55 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 6B1395H-STD | ACL Race - Untreated | Standard | 1.793 |
| 6B1395HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.780 |
| 6B1395H-.025 | ACL Race - Untreated | +0.025 | 1.806 |
| 6B1395H-.25 | ACL Race - Untreated | +0.25 | 1.918 |
| 6B1395H-.50 | ACL Race - Untreated | +0.50 | 2.043 |
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 | 0.053 to 0.063 mm |
| Increased clearance (HX) | Wider clearance: high oil flow, high rpm | 0.078 to 0.088 mm |
| +0.025 mm | Polished journal | 0.053 to 0.063 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.053 to 0.063 mm |
| +0.50 mm | Journal reground to 0.50 mm | 0.053 to 0.063 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, +0.25 and +0.50 mm regrind sizes 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 N52 and N53 six-cylinder engines of the following BMW models:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| BMW | 1 (E81) | N52B30 | 258–265 hp | 2006–2011 |
| BMW | 1 (E87) | N52B30 | 258–265 hp | 2005–2011 |
| BMW | 1 Coupe (E82) | N52B30 | 218–234 hp | 2007–2013 |
| BMW | 1 Convertible (E88) | N52B30 | 218–234 hp | 2007–2013 |
| BMW | 3 (E90) | N52B25, N52B30, N53B30 | 177–272 hp | 2004–2011 |
| BMW | 3 Coupe (E92) | N52B25, N52B30, N53B30 | 177–272 hp | 2006–2013 |
| BMW | 3 Convertible (E93) | N52B25, N52B30, N53B30 | 177–272 hp | 2006–2013 |
| BMW | 3 Touring (E91) | N52B25, N52B30, N53B30 | 177–272 hp | 2004–2012 |
| BMW | 5 (E60) | N52B25, N52B30, N53B25, N53B30 | 177–272 hp | 2004–2010 |
| BMW | 5 (F10) | N52B25, N52B30, N53B30 | 204–272 hp | 2009–2013 |
| BMW | 5 Touring (E61) | N52B25, N52B30, N53B25, N53B30 | 177–272 hp | 2004–2010 |
| BMW | 5 Touring (F11) | N52B25, N52B30, N53B30 | 204–272 hp | 2009–2013 |
| BMW | 6 (E63) | N52B30, N53B30 | 258–272 hp | 2004–2010 |
| BMW | 6 Convertible (E64) | N52B30, N53B30 | 258–272 hp | 2004–2010 |
| BMW | 7 (E65, E66, E67) | N52B30 | 250–258 hp | 2005–2008 |
| BMW | 7 (F01, F02, F03, F04) | N52B30 | 258 hp | 2009–2015 |
| BMW | X1 (E84) | N52B30 | 218–264 hp | 2009–2011 |
| BMW | X3 (E83) | N52B25, N52B30 | 211–272 hp | 2006–2010 |
| BMW | X3 (F25) | N52B30 | 258 hp | 2011–2012 |
| BMW | X5 (E70) | N52B30 | 234–272 hp | 2006–2012 |
| BMW | Z4 Coupe (E86) | N52B30 | 218–265 hp | 2006–2009 |
| BMW | Z4 Roadster (E85) | N52B25, N52B30 | 177–265 hp | 2005–2009 |
| BMW | Z4 Roadster (E89) | N52B25, N52B30 | 204–265 hp | 2009–2011 |
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.
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Reference6B1395H-STD
