Rod Bearings

Has the crankshaft been ground undersize, or do the connecting rods need new bearing shells during a rebuild? In this category you will find rod bearings in standard size and various oversize/undersize fitments for petrol and diesel engines, so the bearing can be matched to the actual dimensions of the crankshaft.

What rod bearings do in the engine

The rod bearing sits between the connecting rod and the crankpin and carries the force the piston sends down with every combustion. A thin oil film separates the bearing from the journal, so material, coating and clearance affect how well the engine handles high revs and increased boost pressure. Bearings for the crankshaft main journals can be found under main bearings, while thrust bearings control the crankshaft's lateral movement.

How to choose rod bearings

• Size: The designation, e.g. standard, 010 or +0.50mm, must match the crankshaft dimensions after any grinding. Always measure the journals before you order.
• Engine code: The bearings are engine-specific, e.g. sets for Subaru EJ20/EJ22/EJ25 or Mitsubishi 4B11T. Check the engine code and number of cylinders.
• Load: For higher-power projects, performance sets are available, e.g. from King Engine Bearings with pMaxKote coating or the ACL High Performance series. The choice depends on power target, revs and oil pressure. The category also includes bearings from Clevite and OMIX.

Installation and clearance

Oil clearance should be checked during installation, e.g. with Plastigauge strips or a micrometer and dial bore gauge, and compared with the engine manufacturer's specification. The back of the bearing shells must be clean and dry, while the running surface is lubricated with assembly lube. Typically replace the entire set at once, and find other bearings and spacers under bearings and bearing spacers.

Frequently asked questions

How do I know whether I need standard or undersize bearings?

It depends on the crankshaft dimensions. If the journals have been ground, the bearing size must correspond to the grinding. Measure the journals with a micrometer and compare the result with the engine's specification before choosing a size.

Can I reuse old rod bearings?

It is typically not recommended. Bearings wear in against the journal they have run on, and scoring, discolouration or exposed base material can indicate lubrication problems. When an engine is disassembled, they are normally replaced as a complete set.

What can cause a rod bearing to fail?

Typical causes are low oil pressure, contaminated oil, incorrect clearance or overheating. Find the cause before you install new bearings, otherwise the damage may recur on the new set.