Engine Bearings

Is there a knock deep down in the engine, or has the crankshaft been ground and is ready for assembly? This category contains rod bearings, main bearings, camshaft bearings and thrust bearings for engine rebuilds and projects with more power. The bearings support the rotating parts on a thin oil film, so your choice can affect both oil pressure and durability.

What engine bearings do

The plain bearings in the engine are thin shells that sit between the crankshaft journals and the block or the connecting rods. Rod bearings and main bearings carry the load from the pistons and crankshaft on an oil film, while camshaft bearings support the camshaft. Thrust bearings and thrust washers control the crankshaft's lengthwise movement, e.g. ACL's thrust washer for the Mitsubishi 4B11T Evo X / Hyundai Genesis.

How to choose bearings

Start with the engine code and the measurement of the crankshaft journals. Bearing sets are available in standard size and in a range of sizes for ground or modified journals, specified as e.g. STD, STDX, .001, 0.25 mm and +0.020. Which size you need depends on the journal diameter, the bore in the block and connecting rod, and the oil clearance the engine builder is aiming for. Key criteria:

• Engine code: e.g. Mitsubishi 4G91/4G92/4G93, 4B11T, Toyota 2ZZGE, Ford/Mazda 2.0L/2.3L Duratec or GM 6.2 LT1/LT4.
• Series and version: e.g. ACL High Performance and Race Series or King XP-Series and pMaxBlack-coated sets.
• Use: daily driving, track days or a project with higher boost pressure can place different demands on clearance and oil.

Installation and maintenance

Measure the clearance during assembly, e.g. with a micrometer and dial bore gauge or Plastigage, and check the journal surfaces on the crankshaft. Clean the oil passages thoroughly so dirt doesn't end up in the new bearings, and lubricate the bearing surfaces with assembly lube during assembly. A well-functioning oiling system and regular oil changes have a major impact on how long the bearings last. The category also includes brands such as Clevite, Hot Rods and All Balls Racing.

Frequently asked questions

What do the sizes of the bearing sets mean?

The size indicates which journal dimension the set is intended for, e.g. STD for standard size or a size such as 0.25 mm for a ground crankshaft. Always choose based on the measurements of the specific engine.

Can I reuse the old bearings during an engine rebuild?

This is typically not recommended. Bearings wear in against the journals they have run on, and even small scratches or embedded dirt can change the oil clearance. During a rebuild, the bearings are normally replaced along with a new measurement.

Why does the clearance need to be measured when the set fits the engine code?

Because the tolerances of the block, connecting rods and crankshaft vary. The actual clearance depends on all the parts together, so it should be checked during assembly before the engine is started.

What are the signs of worn engine bearings?

Dropping oil pressure, knocking from the bottom end of the engine or metal shavings in the oil and oil filter can indicate bearing wear. The cause can also lie elsewhere, so the engine should be inspected before you order parts.