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A Series - 12YD APJM BM7
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A Series - 12YD APJM BM7
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Set of 6 trimetal crankshaft main half-bearings for Leyland A Series.
ACL lists main bearing set 3M2203H for the Leyland A Series four-cylinder engines. They share the same crankshaft journal diameter: a single set covers the whole family.
The crankshaft of these engines runs on three main bearings. Each journal turns between two half shells, one seated in the block and the other in the main bearing cap: they carry the crankshaft. The ACL Race Series tri-metal set shown here replaces them on built engines.
A tri-metal 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 covers the three main bearings of the crankshaft.
An aluminium bi-metal takes around 8,000 psi, a performance tri-metal up to 12,000 psi, 50% more. Hence better resistance and better durability on turbocharged, supercharged and high-revving engines.
| ACL bearings Crankshaft journal Ø 44.463 / 44.475 mm Housing bore Ø 48.158 / 48.171 mm Width 27.1 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 3M2203H-STD | ACL Race - Untreated | Standard | 1.828 |
| 3M2203HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.815 |
| 3M2203H-001 | ACL Race - Untreated | +0.025 | 1.8407 |
| 3M2203H-010 | ACL Race - Untreated | +0.25 | 1.955 |
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 | 0.049 to 0.057 mm |
| Increased clearance (HX) | Wider clearance: high oil flow, high rpm | 0.074 to 0.082 mm |
| +0.025 mm | Journal reground to 0.025 mm | 0.049 to 0.057 mm |
| +0.25 mm | Journal reground to 0.25 mm | 0.049 to 0.057 mm |
Checking on assembly: lay a calibrated strip (Plastigauge) on the journal, torque the main cap to spec, then compare the crushed strip against the gauge to read the clearance.
The ACL main 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 main bearing set fits the following vehicles, by engine code:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| Leyland | All models | A Series |
