LONG BLOCK M 20R4277 - Caterpillar

EnginesDuring the installation of a new cylinder block as a replacement for a damaged block, many dealers have desired a recommendation on the installation of new main bearings. This can be a problem when the bearings in the former cylinder block are in good condition and are not badly worn.
In the past, for some specific conditions, the recommendation has been given to install the used bearings, but this recommendation will no longer be made. Tests and inspections made during a period of time show that the installation in a new cylinder block of bearings that have been used in a different block can cause problems and is not generally practical.
When a cylinder block is machined at the factory, necessary tolerances cause small differences between cylinder blocks. These differences can change several factors that have an effect on bearing wear, including stress points, wear areas, clearances, bearing crush and possibly taper in the bearing bores. Because of these wear factors, bearings which have been used in one cylinder block can have a shorter service life when installed in a different cylinder block.
For this reason, the recommendation is to install new main bearings during installation of a replacement cylinder block. The use of new bearings in a new block is the best procedure to be sure the bearings will give maximum service life.