12896 Mercury SCREW, SWITCH

Start By:a. remove piston cooling jets In some cases, seagoing vessels require periodic main bearing inspection. Normally bearing inspection would be difficult because of the inaccessibility and weight of the main bearing caps. The FT1794 Crankshaft Main Bearing Removal Tool Group simplifies this inspection procedure. See Special Instruction, Form No. SMHS8331, for the complete inspection procedure.1. Drain the oil from the pan. 2. Use tool (A) to turn the engine flywheel to move counterweights (1) in position for removal. Remove counterweights (1) from the crankshaft through the side of the cylinder block.3. Use tool (A), and turn the engine flywheel to move the connecting rod bearing surface (journal) to the top center position. 4. Use tool (B), and loosen the four bolts that hold the main bearing cap in position.5. Hold the main bearing cap in position with a pry bar, and remove the bolts. Lower the bearing cap from the cylinder block.6. Remove the bearing caps from the side of the engine. The weight of each bearing cap is 16 kg (35 lb.). 7. Remove lower bearing half (2) from bearing cap (3). 8. Remove thrust plates (4) from each side of the center main bearing.
If the crankshaft is turned in the wrong direction, the tab of the bearing will be pushed between the crankshaft and cylinder block. This can cause damage to either or both.
On the center main journal that has no oil hole, put a thin piece of soft material that will not damage the crankshaft journal against the end of the bearing, opposite the tab. Hit the bearing with the soft material until the tab of the bearing is free from the cylinder block. Remove the upper half of the main bearing. 9. Install tool (C) in the oil hole in the crankshaft journal, and remove upper main bearing halves (5) as the crankshaft is turned and the bearing is moved out of the cylinder block.Install Crankshaft Main Bearings
Make sure the upper and lower bearings are installed so the bearing tabs fit into the notch in the cylinder block and bearing caps. Install the main bearings dry when clearance checks are made. Put clean engine oil on the main bearings for final assembly. For complete details concerning measuring bearing clearances, see Engine Bearings And Crankshafts, Form No. SEBD0531.
1. Install tool (B) in the oil hole of the crankshaft. Put the upper bearing half (half with oil hole) in position on the crankshaft. Use tool (A) to turn the engine flywheel, and push the bearing half in position with tool (B).2. Make sure the bearing caps are clean, and install the lower bearing halves in the caps.
When Plastigage is used to check bearing clearances, do not use an impact wrench for the torque tightening sequence.
When the bearing clearance is checked and the engine is in a vertical position, such as in the vehicle, the crankshaft will have to be lifted up and held against the upper halves of the main bearing to get a correct measurement with the Plastigage. The Plastigage will not hold the weight of the crankshaft and give a correct indication. If the engine is in a horizontal position, it is not necessary to hold the crankshaft up. Do not turn the crankshaft when the Plastigage is in position to check clearances.3. Check the bearing clearances with Plastigage as follows:a. Put a piece of the Plastigage on the surface of the lower bearing half.b. Install the main bearing caps with the word "FRONT" and the cast part number toward the front of the cylinder block. Each cap has a number on the bottom surface and must be installed in the same position as the correct number on the right side of the block pan rail.c. Put 6V4876 Molykote Paste Lubricant or Fel-Pro C100 Lubricant on the main bearing cap bolts, and hand tighten them in the number sequence shown with tool (D) to a torque of 136 14 N m (100 10 lb ft). Then hand tighten the bolts in the number sequence shown 180 5° of a turn more.d. Remove the caps and measure the Plastigage. The main bearing clearance must be 0.122 to 0.241 mm (.0048 to .0095 in.). 4. Put clean engine oil on thrust plates (5), and install them on each side of the center main bearing with the grooves in the plates against the crankshaft. 5. Put clean engine oil on bearings (7), and put bearing caps (6) in position, and tighten the bolts as in Step 3. An impact wrench can be used for the final 180 5° torque tightening turn.
Each counterweight has a number and must be installed in the same position as the correct number on the crankshaft mounting pad to prevent damage to the crankshaft when the engine is run. Also do not use an impact wrench to tighten the bolts the additional 90 5° of a turn more.
6. Make sure the dowels are in position, and install counterweights (8) on the crankshaft. Put 6V4876 Molykote Paste Lubricant or Fel-Pro C100 Lubricant on the counterweight bolt threads, shank and head seat. Tighten the bolts to a torque of 50 5 N m (37 4 lb ft). Tighten the bolts an additional 120° 5° of a turn. 7. Check the crankshaft end play with tooling (C). The end play is controlled by the thrust plates on the center main bearing. End play with new bearings must be 0.17 to 0.63 mm (.007 to .025 in.).8. Fill the engine with oil to the correct level. See the Maintenance Manual for the correct fluid level.End By:a. install piston cooling jets