Piston ring clearances
We have three types of clearance for piston rings. Butt clearance. Axial clearance. Back clearance or radial clearance. 1. Butt clearance : * Is also known as ring end clearance or gap clearance. * It is the distance between connecting faces of piston ring. ( or clearance between the end butt of the ring inside the liner.) * This clearance should be within the limits specified by the engine manufacturer. * The ring expands when the engine is hot. If the clearance is less than the minimum limit, ends touch due to this thermal expansion. * The ring expands against the liner. This increases the friction resulting in breakage of ring and Seizure of piston. * If the clearance is greater than the maximum limit, combustion gases blow by the rings and exhaust gases enter the crankcase. * This results in loss of compression pressure in the cylinder. * To measure butt clearance, insert the rings in the bottom of the liner and ensure that they are in line with the liner axis. * ...
