Repair and Scraping of Crankshaft Bearings for Diesel Engines Part 2

Today, we will continue to introduce the repair and scraping of diesel engine main shaft bearings and crankshaft bearings at a cost.

Good standards

(1) Contact area: Last line: Over 95%; Other channels: More than 75%, with evenly distributed contact points and no significant contact marks.

(2) The gap (tightness) is appropriate.

The inspection method is as follows. Empirical method: Add a thin layer of engine oil to the surface of the bearing shell, and tighten the bearing cover to the specified torque (tightening sequence is the same as above). Use the wrist force of both hands to pull the crankshaft arm, and it is appropriate to make the crankshaft rotate about one turn. Kilogram wrench technique (a relatively reliable method): Use a torque wrench to rotate the bolt at the rear end of the crankshaft where the flywheel is installed, with a torque of 2-3kg · m for the three bearings; 4-way tile 3-4kg. m; 5-watt 4-5kg. m; 6-7kg. m for 6 tiles; 7-8kg. m of 7 tiles is suitable. In addition, there are measurement methods and lead wire and copper foil methods, which have been discussed earlier and will not be repeated here.

After inspection, if the clearance is too small, appropriate scraping should be carried out; If the clearance between the two ends of the bearing is too large, the adjusting shims at both ends of the bearing can be reduced, or a copper sheet of appropriate thickness can be placed on the back of the bearing (not allowed during major repairs), and the bearing can be replaced if necessary. Never file the two ends of the bearing shell cover or seat hole with a file.

There are clear regulations for the radial clearance between the bearing shell and the journal for each model. The size of the clearance is related to the material of the bearing alloy layer, the diameter of the journal, the speed of the diesel engine, and the load borne by the bearing per unit area. But the material of the bearing alloy layer still plays a decisive role. Generally speaking, Babbitt alloy bearing<copper alloy bearing<aluminum alloy bearing<nickel alloy bearing.

The consequences of improper tightness of the axle pad and excessive clearance: oil loss; Oil pressure decreases; Difficulty in forming oil film; The impact load borne by the bearing shell intensifies; Generate knocking sound. The consequences of a too small clearance: difficulty in forming an oil film; Generate half a thousand frictions; The working temperature of the bearing rises; The wear of the bearing shell intensifies; Burning tiles or "holding axles".

The inspection of crankshaft axial clearance, also known as crankshaft end clearance, refers to the axial clearance between the bearing thrust end face and the journal positioning shoulder. It is designed to meet the needs of thermal expansion of diesel engine components during operation. If this gap is too small, it will cause the machine to expand and get stuck; If the clearance is too large and moves back and forth, it will cause abnormal wear to the components of the piston connecting rod group. The surface of the thrust washer will gradually wear, causing the clearance to change and form axial displacement. Therefore, when assembling the crankshaft, the axial clearance of the crankshaft should be checked.

When checking, first align the crankshaft positioning shoulder with one side of the bearing's thrust end face, use a pry bar to pry and squeeze the rear end of the crankshaft, and then use a thickness gauge to measure between the first crankshaft arm and the thrust washer. The axial clearance of the crankshaft is generally between 0.05-0.25mm. If the axial clearance is too large or too small, the thrust washer should be replaced or repaired.

As a professional diesel generator manufacturer, we always insist on using first-class talents to build a first-class enterprise, create first-class products, create first-class services, and strive to build a first-class domestic enterprise. If you would like to get more information welcome to contact us via sales@dieselgeneratortech.com.