Plugs installed in the cooling channels of the unit may be difficult to remove or even not be removed at all.
1. Remove the plugs from the cylinder block. To do this, use a hammer and a punch to hit the inside of the block on one side of the plug, grab the other edge with large pliers and pull it out.
2. Remove all traces of gasket material from the cylinder block with a scraper. Be very careful not to leave scratches or dents on the sealing surfaces.
3. Remove covers of radical bearings and separate loose leaves of bearings from covers and the block of cylinders. Make a note of which cylinder the bearings belong to and whether they were installed in the cap or in the block, then set aside.
4. Remove all oil line plugs from the block. Plugs are usually very tight - you may need to drill them and clean the holes with a tap. When assembling the engine, use new plugs.
5. If the engine is heavily soiled, it should be sent to a mechanical workshop for steam cleaning.
6. After returning the unit from the mechanical workshop, clean the holes and channels of the oil lines again. Most auto supply stores have special brushes. Flush the channels with water until it comes out clean, dry the block thoroughly, and coat all milled surfaces with a light anti-corrosion oil. If compressed air is available, use compressed air to speed up drying and blow through all openings and oil lines.
Protect your eyes when using compressed air!
7. If the unit is not heavily soiled or contaminated with dirt, appropriate cleaning can be done with hot soapy water and a stiff brush. Do this work carefully and allocate enough time for it. Regardless of the cleaning methods, make sure that all holes and oil lines are cleaned very thoroughly, the block is completely dry and the treated surfaces are covered with a light oil.
8. Threaded holes in the block for accurate measurements of tightening forces during assembly must be cleaned. To remove rust, corrosion, thread compound, or dirt, install an appropriately sized tap in each hole. If possible, clean the holes of debris with compressed air after this operation. Make sure all holes are dry - oil or other liquid can cause the unit to crack due to hydraulic pressure when the bolts are tightened. Now it's the turn to clean the threads of all the bolts. Note that BMW recommends replacing the cylinder head and main bearing bolts with new ones.
9. Install the main bearing caps and tighten the bolts by hand.
10. After applying a suitable compound to the sealing surfaces, install them in the block. Be sure they are installed flat and as far as they will go, otherwise leakage may occur. There are special tools for this, however, a socket that can be inserted into the plug, a 1/2 inch extension and a hammer can also be successfully used.
11. Apply a non-drying sealant to the new oil line plugs and screw them into the holes in the block. Make sure they are securely tightened.
12. If the engine is not going to be assembled further, cover the unit with a large plastic bag to keep it clean.