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3.0L 24v - N52B30
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3.0L 24v - N52B30
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Set of 12 trimetal connecting rod half-bearings for BMW inline six N52 and N53.
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.
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 12 half shells, six pairs for a six-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 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 |
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 | 0.053 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.
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 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 |
