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2.5L 8v - M44
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2.5L 8v - M44
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Set of 8 trimetal connecting rod half-bearings for Porsche 924 S and 944.
The M 44 engines (2.5, 2.7 and 3.0-litre) of the Porsche 924 S and 944, Turbo versions included, are inline four-cylinders producing 150 to 250 hp. ACL lists the same bearing set for all these engines: a single set covers the 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.
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.
| ACL bearings Crankpin Ø 51.971 / 51.990 mm Housing bore Ø 55.000 / 55.019 mm Width 24 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 4B2475H-STD | ACL Race - Untreated | Standard | 1.497 |
| 4B2475HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.484 |
| 4B2475H-.025 | ACL Race - Untreated | +0.025 | 1.510 |
| 4B2475H-.25 | ACL Race - Untreated | +0.25 | 1.624 |
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 | 0.055 to 0.065 mm |
| Increased clearance (HX) | Wider clearance: high oil flow, high rpm | 0.080 to 0.090 mm |
| +0.025 mm | Polished journal | 0.055 to 0.065 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.055 to 0.065 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 924 S and 944 inline four-cylinder engines of the following Porsche models:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| PORSCHE | 924 2.5 S | M 44.07, M 44.08, M 44.09, M 44.10 | 150–160 hp | 1985–1988 |
| PORSCHE | 944 2.5 | M 44.01, M 44.02, M 44.03, M 44.04, M 44.05, M 44.06, M 44.07, M 44.08, M 44.09, M 44.10 | 150–163 hp | 1981–1990 |
| PORSCHE | 944 2.5 S | M 44.40 | 190 hp | 1986–1988 |
| PORSCHE | 944 2.5 Turbo | M 44.50, M 44.51, M 44.52 | 220–250 hp | 1985–1991 |
| PORSCHE | 944 2.7 | M 44.11, M 44.12 | 165 hp | 1988–1989 |
| PORSCHE | 944 3.0 S2 | M 44.41 | 211 hp | 1988–1991 |
| PORSCHE | 944 Convertible 2.5 Turbo | M 44.52 | 250 hp | 1990–1991 |
| PORSCHE | 944 Convertible 3.0 S2 | M 44.41 | 211 hp | 1988–1991 |
