Manual - Chapter 1 Engine

8. Dismantling the engine unit: removing the camshafts and cam chain

  1. If the engine unit is in the frame, remove first the engine outer covers, as described in Section 6 - removing the outer covers of this Chapter. Remove the spark plugs, as described in Routine Maintenance - Check the spark plugs.
  2. Rotate the crankshaft by means of an Allen key placed in the ignition rotor retaining bolt until the camshafts are placed so that all valves are closed as far as possible, ie so that there is the minimum pressure possible exerted on the camshafts by the valve springs. On 75 models this position is close to Number 3 cylinder being at TDC on the compression stroke.
  3. Remove the chain tensioner. Some early 100 models are fitted with a chain tensioner which can be locked by turning a screw as far as possible clockwise; the tensioner mounting screws are then removed and the unit can be withdrawn. The screw is to be found in that face of the tensioner opposite to the plunger/tensioner blade assembly. On 75 models and later 100 models compress the tensioner by hand, remove the mounting screws and withdraw the unit; slowly allow it to extend until the spring pressure is released.
  4. Remove their retaining clips or circlips, noting the washer behind each, and withdraw the cam chain tensioner blade and chain guide. Remove its retaining screws and withdraw the chain top guide rail from between the camshafts; these are Torx screws which BMW state are size T30 but were found on the machine featured in the accompanying photographs to be size T27. Owners should ensure that both sizes of key are available.
  5. In some cases there may be sufficient slack in the chain, and sufficient clearance around the sprockets, to permit its removal at this stage but usually it will be necessary to withdraw the camshaft sprockets; use an open-ended spanner to hold the camshaft at the hexagon provided, remove the bolt and withdraw the large washer and the sprocket. While these components are the same for both intake and exhaust camshafts, it is good practice to mark them and to store them separately so that they can be refitted in their original locations. Withdraw the chain from the crankshaft sprocket.
  6. If required, the ignition rotor flange end crankshaft sprocket can be withdrawn at this stage.
  7. If the camshafts are to be removed, this can be done before or after the chain has been disconnected but in the former case some care will] be required to avoid damaging or marking any components.
  8. Note: Before removing the camshafts make a careful note (using a small sketch if required), of the exact location and fitted position of the bearing caps; these are clamped to the head and line-bored in a single process on manufacture and must not be refitted on any other bearing, nor reversed. The manufacturer has provided identification aids in the form of a number stamped into each bearing cap to match a number cast into the cylinder head next to the bearing pedestal; these numbers are stamped in the top of each cap above the threaded boss on the intake and below it on the exhaust and can only be read from the rear of the cylinder head looking forwards to help eliminate any possibility of their being reversed. Note that odd numbers are used for the intake and even numbers for the exhaust, except for the rear bearing on 100 models which is marked 'O' indicating '10'. If necessary, make your own identifying marks, provided this does not involve scratching a cap or using a punch. It is useful to have ready some means of retaining the cam followers and shims. See paragraph 12.
  9. To avoid tilting the camshafts, remove first the front or cam chain end (thrust) bearing caps. Unscrew the nuts alternately by a turn at a time so that each bearing is released evenly and remains square. Note the locating dowels fitted at each stud of these front bearing caps. Store the caps in separate, clearly marked containers.
  10. With the front bearings removed, gradually and evenly slacken the nuts on the remaining bearing caps, working from the outside inwards until alt valve spring pressure is released. Withdraw the caps and store them in separate clearly-marked containers.
    Note: take a great deal of time and trouble over this - if any bearing cap is cracked or damaged by careless workmanship it can only be replaced as part of a new cylinder head assembly.
  11. Withdraw the camshafts. There is no need to mark them as the bearings are offset and the cams can be refitted only in the correct location.
  12. If the camshafts are to be removed, it is worthwhile to cut two lengths of wooden dowel, of a diameter similar to that of the camshaft rear bearings, and to fasten these lightly in place using the bearing caps. This wilt avoid the loss of any components and the risk of the cam followers and shims failing out and getting mixed up.

8.4 Cam chain top guide rail is retained by Torx screws - ensure correct size key is available

8.5 If sprockets are to be removed, hold camshaft as show while retaining bolts are unscrewed

8.8 Identify camshaft bearing caps using marks provided (arrowed) before disturbing - make notes if required

8.11 Withdraw camshafts separately to avoid mixing components - Camshaft bearings are offset, so cams themselves cannot be interchanged