Manual - Chapter 1 Engine

32. refitting the camshafts and setting the valve timing

  1. Remove the wooden dowels (if used) from the camshaft locations. Layout all the bearing caps with their nuts and washers, keeping separate intake and exhaust components and remove all traces of dirt from the bearing surfaces and cam followers. Refit all four dowel pins to the cylinder head.
  2. Remove each cam follower bucket in turn and check that the adjustment shim is correctly seated with its marked face downwards. These shims are easily displaced and can cause a lot of trouble if not checked at this stage. If work has been done on the valve gear, making it necessary to check the valve clearances, do not forget to do this at the appropriate time, the work necessary being described in Routine Maintenance.
  3. Check that number 3 cylinder (75 models) or number 1 cylinder (100 models) is at top dead centre (TDC). Pack the spark plug channel with clean rag or similar so that oil cannot enter, and check that the blanking plug is securely fixed in the rear end of each camshaft.
  4. Positioning the camshaft so that its lobes are pointing away from all valves as much as possible, copiously oil the bearing surfaces of the cylinder head, caps and camshaft and offer up the first camshaft, refit the rear bearing caps (ie not yet the front thrust bearing caps) and, when possible, the retaining nuts and washers. Ensure that the number in each bearing cap matches the number cast into the cylinder head next to the bearing pedestal and that the number is above (intake) or below (exhaust) the threaded boss and can be read only from the rear; this ensures that the caps are installed in exactly the same way as they were originally fitted. See the accompanying photographs and illustrations for details.
  5. Working evenly and gradually, by a turn at a time, tighten the nuts of the inner bearing caps first (ie first and second from the front on 75 models, second and third from the front on 100 models) in a diagonal sequence. As the camshaft is tightened on to its bearings against valve spring pressure prevent any risk of its tilting by lightly tightening the nuts of the outer bearing caps. When the inner bearing caps are seated securely on the cylinder head, tighten the outer cap retaining nuts until all rear caps are seated, then lubricate and fit the front (thrust) bearing cap. When all caps are seated, tighten their retaining nuts in the same sequence to the specified torque wrench setting; be careful to maintain the same even application of pressure. 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.
  6. Copiously lubricate its bearing surfaces and refit the second camshaft as described above.
  7. Slowly and carefully rotate each camshaft using an open-ended spanner on the hexagon provided, until the lobe for number 3 cylinder (75 models) or number 1 cylinder (100 models) is pointing away from its valve but is inclined slightly inwards towards the opposite camshaft. If resistance is encountered at any point stop and turn the crankshaft backwards so that there is sufficient clearance between the piston and valve for the camshaft to continue rotating. Do not apply any extra force other than that normally required to rotate the camshaft; there is a risk of damaging the valves or pistons if they are forced against each other.
  8. When both camshafts and the crankshaft are thus positioned approximately so that number 3 or 1 cylinder (as appropriate) is at TDC on the compression stroke (both valves closed) refit the camshaft sprockets. If the cam chain can be removed and refitted with the sprockets in place they can be fully secured at this stage; if not they should be refitted loosely as they will have to be removed and refitted during the valve timing procedure. To fit the sprockets, place each one on its respective camshaft, aligning the locating pin protruding from the sprocket rear face with the camshaft keyway, then refit the large washer with its recessed face against the sprocket. Refit the sprocket retaining bolt and, holding the camshaft by applying an open-ended spanner to the hexagon provided, tighten the bolt to the specified torque setting.
  9. Rotate the camshafts until the marks on the sprockets are aligned exactly with the cylinder head top (ie left-hand, when installed) machined surface, ie the joint between the head and the front (thrust) bearing caps. See the accompanying photograph. Rotate the crankshaft until the ignition rotor flange locating pin aligns exactly with the centre rib cast in the cylinder block/crankcase; as can be seen from the accompanying photographs, later models have a more precise mark cast on the crankcase wall, closer to the flange for easier alignment (OT is the German equivalent of TDC). These are the valve timing marks, with number 3 or 1 cylinder exactly at TDC on the compression stroke; check regularly that all are aligned exactly as the chain is refitted.
  10. Engage the cam chain on the sprockets so that the runs between the crankshaft and intake camshaft and the two camshafts are as taut as possible while all three shafts are aligned with their marks. In some cases, as previously noted, this will require the removal and refitting of the camshaft sprockets; proceed as described in paragraph 8 above.
  11. To ensure that the chain runs are absolutely taut, it may be necessary to rotate the driven sprocket slightly towards the driving sprocket, ie intake cam sprocket towards crankshaft, exhaust cam sprocket towards intake, so that the chain can be fitted and the driven sprocket can be rotated forwards again until its timing mark aligns. However, depending on the degree of wear in the chain this may not be possible and some error will be inevitable as the chain wears. If the marks are no more than one tooth out they are as close as production tolerances will permit.
  12. Fit the chain tensioner blade to its pivot and press it hard, by hand, against the chain lower run to take up any slack. Applying an Allen key to the ignition rotor flange retaining bolt, rotate the crankshaft slowly forwards (anticlockwise, looking at the rotor flange from the front of the machine) through a full cycle until number 3 (75 models) or 1 (100 models) cylinder is again at TDC on the compression stroke and the timing marks are all aligned. If resistance is encountered, stop immediately and find out the cause. If a valve is touching a piston the valve timing is incorrect and the procedure must be repeated until the error is found and rectified.
  13. If the timing marks align exactly (or so closely that the error cannot be corrected by moving even one tooth at the driven sprocket) the valve timing is correctly set. Secure the chain tensioner blade by refitting its washer and retaining clip.
  14. Refit the chain guide blade noting the washer under each retaining clip or circlip. Refit the chain top guide rail and tighten securely its retaining Torx screws; use the torque wrench setting, where specified.
  15. Rebuild the chain tensioner assembly. On the later type, without a locking screw, insert the plunger ratchet into the tensioner body, and place the spring inside the ratchet bore. Ensuring that the spring does not snag on the plunger guide pin, insert the plunger into the tensioner body, over the ratchet, until the guide pin engages with the curved slot in the ratchet. Press the plunger fully into the tensioner body, allowing it to twist as its guide pin follows the ratchet slot. When it is seated fully in the tensioner body, rotate the plunger clockwise until its head is square to the tensioner body with the two small tangs on the outside (see the accompanying photographs). Hold the assembly compressed while it is placed on the crankcase, noting that the plunger tangs match with the moulded extensions from the tensioner blade plastic face so that there is no metal-to-metal contact between the plunger and blade. Refit and tighten securely the tensioner mounting screws; use the torque wrench setting, where specified. Press the blade firmly against the chain run; the tensioner should extend to take up the slack.
  16. On the early type of tensioner, fit the assembly exactly as described above but note that the plunger will not extend until the locking screw has been turned fully anticlockwise to release it.
  17. Refit the engine outer covers and the spark plugs.


32.3 Check that blanking plug in securely fixed in each camshaft rear end


32.8a Note correct position of cam lobes when cylinder is at TDC on compression stroke - number 1 cylinder, 100 models shown


32.8b Align locating pin on sprocket rear face with camshaft keyway...


32.8c ...and fit large washer with recessed face against sprocket


32.8d Tighten sprocket retaining bolts to specified torque wrench setting


32.9a Rotate camshafts until notches in sprockets align exactly with bearing cap/cylinder head joints (arrowed)


32.9b Rotate crankshaft until ignition rotor locating pin aligns with fixed crankcase mark  when appropriate piston is at TDC


32.10 Refit the cam chain without disturbing timing mark alignment and so that chain runs are taut, see text


32.12 Fit chain tensioner blade and rotate engine to check valve timing...


32.13 ...if correct, secure blade with large washer and retaining clip, as shown


32.14a Chain guide blade is fitted over chain ...


32.14b ...and is secured with a washer and retaining clip at each mounting


32.15a Reassemble tensioner as described in text - later type shown ...


32.15b ... and refit, ensuring that plunger tangs engage on plastic lugs


32.15c Tighten tensioner retaining screws securely