DieselShip

When a piston is removed from an engine during the overhaul of a cylinder unit the shape of the piston crown is examined and compared with a gauge showing its proper shape and its height above some datum
If the shape and height are not within the recommended limits the piston is taken out of service and sent to one of the specialist firms dealing with piston repair.The firm will gauge the piston, examine it for fractures or cracks, examine the piston ring grooves and note the general condition of the piston. A decision based on estimated repair costs will be made as to whether it warrants repair. It is decided to repair the piston, the crown will be welted up with a deposit of weld metal to bring it to its correct shape and height above datum. The piston – ring grooves will also be welded up. After the welding is completed it will be examined again and if in order it will be heat treated; fully machined and the piston – ring grooves will be chromium plated again.
A repaired piston is similar in appearance to a new piston and has the same expected life. The specialist repair work usually costs considerably less than a new piston. Engine builders and their accredited repairers usually hold stocks of repaired pistons for exchange with pistons that require repair. This shortens the delivery or lead time for the repair of a piston.