FUSO 4M4 – Engine – STRUCTURE AND OPERATION – Crankcase, Crankshaft and Main Bearing

9.1 Crankcase
• The crankcase is a bi-block type consisting of an upper crankcase and a lower crankcase that are assembled to grip the crankshaft in between.
• The upper crankcase has cylinders whose surfaces are machined for direct contact with sliding pistons.
The walls of the cylinders have water jackets for cooling the cylinders.
• The main cap bolts that hold the upper crankcase and the lower crankcase together must be tightened according to the specified procedure.

• The upper crankcase is provided with piston size marks “A”, “B” and “C” stamped to help to select appropriate pistons.

9.2 Crankshaft
• The crankshaft has two sets of color marks. Color mark A indicates the outside diameter of the journals (at five locations), and color mark B indicates the outside diameter of the pins (at four locations).

9.3 Main bearing
• Each upper main bearing has an oil hole, which provides a passage for engine oil to the corresponding crankshaft journal.
• Main bearings of different thickness are available so that the most appropriate ones can be selected to ensure proper clearance between them and journals.
Bearing thickness classes are identified by color marks (red, blue and yellow) painted on the sides of the bearings.
• All the upper and lower main bearings are identical except for the No. 3 upper bearing and the No. 3 lower bearing.

9.4 Thrust plates
• Two upper and lower thrust plate pairs are installed on both sides of the upper and lower main bearings at the rear most journal of the crankshaft.
• The thrust plates must be of a thickness that corresponds to the end play of the crankshaft.
Each thrust plate has two oil grooves to ensure its minimum friction against the crankshaft journal.


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