LO 5-5 Explain the differences between types of machine fits

1. Precision Machine Fits

Precision Machine Fits

In engine construction, the contact surfaces of many of the parts are used to either lock components together or require some movement. When movement between parts is necessary, the precision clearances are classified as sliding or running fits . When firm contact between parts holds or locks them together, absence of any clearance is classified as an interference fit. An example of an interference fit is a piston pin that is made slightly larger than the hole in the piston. Heat and/or force are required to assemble the two parts. In contrast, an example of a running fit is a crankshaft journal and bearings. These two components require space between the parts for oil to circulate. Sliding fits require almost no clearance. The ball and socket joint of a pushrod and rocker lever is an example of a sliding fit.