What Is a Short Block and How Is It Best Used?

Replacement engines for tractors, combines and other heavy duty equipment are available in different configurations and types. The choice on which to choose will depend on several factors, including the damage to the present engine, and how much down time can be absorbed

A problem that sometimes necessitates an engine block replacement arises from loose main bearings, which when spun out, can cause a broken connecting rod that violently breaks and punches through the side of the engine block. There has been examples where the connecting rod punches up into the cylinder head.

In such examples, all other engine components are in perfect working condition, however, the bottom section of the engine needs to be replaced. In engine terminology, the bottom section of the engine is called a short block. Large tractor engines are typically made up of four major components, joined together by smaller components and with accessories attached to the external areas of the engine.

The four major components of a large tractor engine are the cylinder head at the top, the cylinder block under the cylinder head, the crankcase under the cylinder block, and the oil pan at the bottom of the crankcase

The short block engine comprises two of these, namely the cylinder block, and the crankcase. In the automotive field and lawn mower manufacturer which uses small engines, the cylinder block and the crankcase is casted as a single casting during manufacture. However, in large tractor engine and marine engine manufacture, the cylinder block and the crankcase are manufactured as separate castings and then joined afterwards by welded steels plates and precision heavy duty welding. The cylinder block and the crankcase serve different complimentary functions.

The cylinder block is the section of the engine that houses the cylinder liners, the piston assembly and the camshaft. The top section of the cylinder block is called the combustion chamber. On the top of this assembly is bolted the cylinder head. The cylinder head is not a part of the short block engine.

The bottom section of the short block engine is the crankcase. This section of the engine houses the crankshaft, main bearings, crank seals, and front gear train. The combination of the cylinder block and the crankcase is called the short engine block. The two components are welded together, and internally, are connected by the connecting rods, hence the term, "connecting" rods. Motive power is transferred from the piston movements to the crankshaft via the connecting rods.

Short engine blocks removed from salvaged tractor yards are called good used short blocks. Used engine short blocks that were totally overhauled, replaced with new or rebuilt internal components, and restored to OEM specifications are called rebuilt short blocks. OEM companies may have their own abbreviations for their engine, i.e., John Deere will refer to their reconditioned engine blocks as John Deere Reman, and Caterpillar will call theirs Cat Reman. OEM Reman products typically carry the new product unlimited use warranty, when installed by the dealer's mechanics.