Manual - Chapter 1 Engine

26. Reassembling the engine unit: general

  1. Before reassembly of the engine unit is commenced, the various component parts should be cleaned thoroughly and placed on a sheet of clean paper, close to the working area.
  2. Make sure all traces of old gaskets have been removed and that the mating surfaces are clean and undamaged. Great care should be taken when removing old gasket compound not to damage the mating surface. Most gasket compounds can be softened using a suitable solvent such as methylated spirits, acetone or cellulose thinner. The type of solvent required will depend on the type of compound used. Gasket compound of the non-hardening type can be removed using a soft brass-wire brush of the type used for cleaning suede shoes. A considerable amount of scrubbing can take place without fear of harming the mating surfaces. Some difficulty may be encountered when attempting to remove gaskets of the self-vulcanizing type, the use of which is becoming widespread, particularly as cylinder head and base gaskets. The gasket should be pared from the mating surface using a scalpel or a small chisel with a finely honed edge. Do not, however, resort to scraping with a sharp instrument unless necessary.
  3. Gather together all the necessary tools and have available an oil can filled with clean engine oil. Make sure that all new gaskets and oil seals
    are to hand, also all replacement parts required. Nothing is more frustrating than having to stop in the middle of a reassembly sequence because a vital gasket or replacement has been overlooked. As a general rule each moving engine component should be lubricated thoroughly as it is fitted into position.
  4. Make sure that the reassembly area is clean and that there is adequate working space. Refer to the torque and clearance setting wherever they are given. Many of the small bolts are easily sheared if over tightened.
  5. BMW now recommend the use of Three Bond 1207 B silicone sealant (formerly Loctite 574) for all mating surfaces which require the use of jointing compound and emphasize that careful work is necessary to prevent oil leaks. All mating surfaces must be cleaned of all traces of old gaskets or of old jointing compound and must be absolutely flat and unmarked. Using a clean, fluff-free cloth soaked in fresh high flash-point solvent wipe over the mating surfaces to remove all traces of old oil or grease. Apply a thin, continuous coat of sealant to the mating surfaces and assemble the parts immediately; tighten the retaining nuts, bolts or screws evenly and progressively to the specified torque settings, where available. Allow the sealant to harden for one hour before running the engine and peel off any surplus sealant from the outside of the joint.
  6. Remember that if the mating surfaces are in good condition there should be no need for a thick film of sealant; the thinnest smear will usually prove sufficient to seal a joint. Sealant is wasted that is pushed out to form a bead on each side of the joint; note that while the bead on the outside is merely annoying and unsightly, proclaiming amateurish work, the bead on the inside is free to break off and block oilways or cause other similar problems.