Manual - Chapter 1 Engine

36. refitting the engine unit to the frame

  1. First check that the frame paint has been scraped away and the metal cleaned at the frame earth point and the bellhousing mounting point. Apply a thin smear of silicone grease at both points to prevent corrosion but to ensure good electrical contact. Many different electrical faults can be caused by a poor earth contact at these two points on these machines.
  2. Next check that all mounting bolts and nuts are completely clean and free from dirt or corrosion, and that the bolt shanks are well greased to aid refitting and to prevent corrosion. Enlist the aid of two or three assistants to ensure safe refitting.
  3. The installation procedure varies slightly according to model. Early (ie 1984 and 1985) 100 models, which have a frame/bellhousing mounting bracket 70 mm (2.7 in) wide, must have both front mountings shimmed. All 75 models and 1986-on 100 models, which have a frame/bellhousing mounting bracket 100 mm (3.9 in) wide, must have shims at the bell housing mounting and for rubber-mounted frames, at the front left-hand engine mounting. Proceed as described in the relevant sub-section below.

Early 100 models

  1. Lower the frame over the engine/transmission unit and refit loosely the mounting bolts, including the rear suspension mounting. While specific mounting points require careful attention on these models, the fit of the frame to the engine/transmission unit should always be checked and corrected if necessary with shims at all points; remember that vibration will be greatly increased if stresses are trapped in a frame member which is distorted by being clamped on to an engine mounting.
  2. Check the fit of the frame/gearbox mountings and of the frame/bellhousing mounting. If significant clearance is found at any point. it must be eliminated using shims of the required thickness placed between the frame and the mounting lug. Note that at the gearbox mountings two thin shims of equal thickness must be used, one on each side, rather than one thick shim, to ensure that the gearbox is exactly central in the frame.
  3. Tighten the rear suspension mounting firmly, the gearbox mountings and the bell housing mounting. Note that BMW recommend a thin coat of copper-based anti-sieze compound such as Copaslip or Never-Seeze for this latter bolt, to prevent corrosion and aid electrical contact.
  4. Check with feeler gauges the gap between each frame lug and its respective engine front mounting boss and install shims of the required thickness to remove it as closely as possible. Shims are available from BMW dealers in 0.25 mm (0.01 in) increments from 1.00 mm (0.04 in) to 5.50 mm (0.22 in) thick. Again, note that rather than use one thick shim to take up all the clearance, two thinner shims of equivalent total thickness should be used, one on each side, to ensure that the engine unit is exactly central in the frame.
  5. When the frame is closely fitted and is seated securely but without stress on all mountings, tighten the mounting bolts or nuts to their specified torque settings.

All other models

  1. Lower the frame over the engine/transmission unit and refit loosely the mounting bolts, including the rear suspension mounting but not yet the engine front left-hand bolt. While specific mounting points require careful attention on these models, the fit of the frame to the engine/transmission unit should always be checked and corrected, if necessary, with shims at all points; remember that vibration will be greatly increased if stresses are trapped in a frame member which is distorted by being clamped onto an engine mounting.
  2. Check the fit of the frame/gearbox mountings. If significant clearance is found it must be eliminated using shims of the required thickness placed between the frame lugs and the gearbox mounting bosses. Rather than use one thick shim to take up all the clearance, two thinner shims of equivalent total thickness should be used, one on each side, to ensure that the gearbox is exactly central in the frame.
  3. Tighten to the specified torque setting the engine front right-hand mounting bolt and the gearbox right-hand mounting bolt.
  4. Use feeler gauges to measure the gap between the frame bracket and the bell housing and insert shims of the required thickness to eliminate the gap as much as possible; the maximum permissible clearance remaining after shimming is 0.25 mm (0.01 in). A range of shims is available from BMW dealers in thicknesses from 1.00 mm (0.04 in) to 5.50 mm (0.22 in) in 0.25 mm (0.01 in) increments. With the gap closed by shims, check that there is clean metal-to-metal contact across the shims between the bellhousing and frame bracket¬ (paint scraped away) and apply a smear of silicone grease to prevent corrosion. Smear the bolt with a thin coat of copper-based anti-seize compound such as Copaslip or Never Seeze, refit it and tighten it to the specified torque setting.
  5. Tighten to the specified torque wrench settings the gearbox left-hand mounting bolt and the rear suspension unit bottom mounting nut.
  6. On all 75 models and K100 models (ie those with rigid engine front mountings) clearance between the frame lug and the engine left-hand front mounting should have been eliminated and the mounting bolt and nut can be refitted and tightened to the specified torque setting. However, if a significant gap is found on any machine it should be closed with shims (as described in paragraph 12 above) before the bolt is fitted and tightened.
  7. On K100 RS, K100 RT and K100 LT models (ie those with rubber bushes at the engine front mountings) the clearance between the frame lug and the engine mounting boss must be measured with feeler gauges and closed as much as possible, using shims of the required thickness; the maximum permissible clearance remaining after shimming is 0.25 mm
    (0.01 in). When the gap has been closed as far as possible refit the mounting bolt and nut and tighten them to the specified torque setting.

All models

  1. Check that the engine/transmission unit is refitted securely and without strain to the frame mountings and that all fasteners are secured to their specified torque wrench settings. Check also that no other components are trapped or distorted, and that the machine is now supported securely on the front wheel and centre stand so that it cannot fall.
  2. Ensuring they are correctly routed and secured neatly out of harm's way by any clamps or ties provided, reconnect to the main wiring loom all electrical components. Use the notes made on dismantling to ensure that components such as the ignition HT coils are correctly reconnected.
  3. Working as described in Routine Maintenance connect the throttle, choke and clutch cables again and adjust them correctly.
  4. Refit the rear mudguard and number plate bracket and the alternator and ignition HT coil covers. Refit the exhaust system as described in Chapter 5 - Fuel & Oil.
  5. Refit the radiator, check that the drain plug is securely fastened and all cooling system components are correctly refitted. Fill the system with coolant (see Chapter 4 - Cooling) and check for leaks. Do not forget to recheck the coolant level after the engine has first been started; accordingly do not fit the radiator cap until this has been done.
  6. Refit the battery (see Routine Maintenance - Battery check) and install the coolant expansion tank. Refit the fuel injection control unit and storage tray. See Chapter 5 - Fuel & Oil. Refit the air intake hose and fasten its single mounting bolt.
  7. Working as described in Routine Maintenance - Oil change, fit a new oil filter element and refill the crankcase with oil. Note that a larger amount than usual will be required if the engine has been dismantled. See Routine Maintenance - Oil check
  8. On those machines so equipped, refit the fairing. See Chapter 7 - Frame & Forks.
  9. Make a final check that all components have been correctly refitted and are correctly adjusted and working properly, where applicable. Refit the fuel tank, the radiator cover panels (where fitted), the side panels and the seat, but remember that the coolant and engine oil levels must be checked after the engine has been run, also that the ignition timing may have to be checked. It will be necessary for example to remove the fuel tank again to check the coolant level at the radiator.

Next Section: Reassembling 37: starting and running the rebuilt engine


36.1a Carefully clean away paint at earth point...


36.1b ...and bellhousing mounting to ensure good earth contact


36.10 Fasten frame to gearbox mountings as described


36.14 on machines with rigid front mountings shims should not be required...


36.15 ...but gap must be eliminated using shims on rubber-mounted engines


36.17a Ensure that all electrical components are connected to wiring loom ...


36.17b ...noting that some connectors can be refitted only the correct way