LO 8-4 Explain the purpose and methods used to increase the rigidity and strength of a diesel engine cylinder block

LO 8-04: Explain the purpose and methods used to increase the rigidity and strength of a diesel engine cylinder block.

Tunnel-Bore Blocks

Tunnel-bore blocks are one of the smoothest-operating and strongest block designs. Integrating the main bearing bores into a single, solid block structure with no bearing caps makes this block the most resistant to distortion in the main bearing bore, as well as the most rigid, to reduce the transmission of noise and vibration. The crankshaft looks like most other crankshafts, but the main bearing journals are each enclosed with a bearing support that wraps around the main bearing and journal. Parting halves of the bearing supports are bolted together to form a circular enclosure that fits snuggly into circular block bores forming the cylinder block’s crankshaft tunnel. The entire crank and the main bearing enclosures are assembled and then lowered into the block’s tunnel during assembly. Locating bolts in the block align oil passageways through the bearing enclosures to the crankshaft and lock the main bearing supports into position Figure 33. Trucks and buses do not use these types of blocks, but Kubota is one manufacturer using these cylinder blocks for its smooth-running, in-line, four-cylinder engines in compact, off-road equipment, such as skid-steer loaders.

FIGURE 08-33: This tunnel-bore engine block has the main bearing bores and block formed into one solid structure for maximum block rigidity and strength.

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