Engine body 4. Turn round the crankshaft until the piston in ques- tion is in the lower turning position. Dismantle the main bearing cap with lower bearing cup. I nspection and matching of piston rings Check the wear surfaces and sides. Black patches on the surfaces imply poor contact and indicate that it is ti me to change the piston rings. The oil consumption is also a critical factor as to when a piston ring should be replaced. Check the piston ring gap (Fig. 41). Push down the ring below the lower turning position by means of a pis- ton. Replace the piston ring if the gap exceeds 1.0 mm (.039 in). Fig. 39. Dismantling of piston 5.
Place a pair of plastic hoses as protection over the connecting rod screws. Carefully tap up the con- necting rod with piston far enough so that the pis- ton rings are released from the cylinder bore. Lift off the piston together with the connecting rod. Note: Scrape off the soot strip in the top part of the cylinder bore to simplify dismantling. 6. Dismantle piston ring with a piston ring tongs. Fig. 41. Checking of piston ring gap Piston rings should also be replaced if there is noticea- ble wear or out-of-roundness in the cylinders since the rings seldom have the same position as they had before dismantling. Check the piston ring gap also on new rings. See "Technical data" for size info.
Check the clearance in the piston ring groove. Roll the ring in its groove in the piston and measure the clear- ance at a number of points with a feeler gauge. Fig. 40. Dismantling of gudgeon pin 7. Remove the circlips for the gudgeon pin and dis- mantle the gudgeon pin carefully with a suitable mandrel. 35