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A Series 12V - 12YE
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A Series 12V - 12YE
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Set of 8 trimetal connecting rod half-bearings for Leyland A Series 12V and 12YE.
These four-cylinder engines are the Leyland A Series 12V and 12YE. ACL lists a single bearing set for these engines: same crankpin diameter, 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.
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 44.460 / 44.473 mm Housing bore Ø 48.146 / 48.158 mm Width 21.59 mm |
| Reference | Brand and treatment | Size | Wall thickness (mm) |
|---|---|---|---|
| 4B2206H-STD | ACL Race - Untreated | Standard | 1.822 |
| 4B2206HX-STD | ACL Race - Untreated | Std, increased clearance (HX) | 1.809 |
| 4B2206H-001 | ACL Race - Untreated | +0.025 | 1.835 |
| 4B2206H-010 | ACL Race - Untreated | +0.25 | 1.949 |
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 0.083 mm |
| +0.025 mm | Polished journal | 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 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 Leyland A Series 12V and 12YE engines of the following models:
| Brand | Model (chassis) | Engine code | Power | Years |
|---|---|---|---|---|
| Leyland | All models | A Series, A Series 12V, 12YE |
