ACL Mitsubishi EVO (4-9) 4G63 7-bolt connecting rod bearings

ACL Race Series bearings are designed for high-performance applications, with a specific focus on racing engines and demanding tuning applications. They are available in various sizes to allow fine-tuning of oil clearance , a critical parameter for engine reliability and performance.

🔧 Types and sizes available:

⚙️ Clearance adjustment by mixing bearings

A common practice among tuners is to mix bearings from adjacent grades (e.g., an upper bearing of one type and a lower bearing of another) to achieve the optimal oil clearance for the engine's specific needs. Here's how to do this adjustment:

• H-STD + H-STD → Standard clearance (baseline).

• HX-STD + H-STD → Increases clearance by +0.0005” (0.013 mm) compared to the H-STD/H-STD pair.

• H-STD + H-001 → Reduces clearance by −0.0005” (0.013 mm) relative to the H-STD/H-STD pair.

• HX-STD + H-001 → Wider combination, allows more extreme adjustments if required.

• Additional combinations → Depending on the configuration, up to 5 different adjustment levels can be achieved in 0.0005” (0.013 mm) steps.

This allows riders and technicians to precisely adjust oil clearance based on:

• Crankshaft tolerances.

• Type of lubricant used.

• Engine preparation level.

• Thermal and load conditions.

🛠️ Recommendations for use and assembly

• The bearing with the greatest thickness must be installed in the area of greatest load :

  • Top of the connecting rod bearing.

  • Bottom (cap) of the main bearing.

• HX-STD sizes are ideal for high-power engines, where the following are expected:

  • Greater block distortion due to inertia and high RPM.

  • Crankshaft deflection under load.

  • Need for increased oil flow and cooling .

  • Use of anti-friction coatings that require additional space.

⚠️ Warning about clearance reduction

Using thinner bearings (such as H-001) may be appropriate in engines with polished crankshafts or low-viscosity lubricants, but caution should be exercised. Reducing clearance also reduces tolerance to block deformation and crankshaft flex under extreme conditions.