Peugeot 405 Manual

Valve clearances - checking and adjustment
XU petrol engine in-car repair procedures / Valve clearances - checking and adjustment


Checking
16-valve models
1 On 1905 cc and 1998 cc 16-valve models, the valve clearances are automatically adjusted by the hydraulic tappet mechanism fitted to each cam follower. Therefore it is not necessary, or indeed possible, to check or adjust the valve clearances manually. If the valve gear has become noisy, a faulty tappet mechanism should be suspected. Refer to Section 10 for further information.

All other models
2 On these models, the importance of having the valve clearances correctly adjusted cannot be overstressed, as they vitally affect the performance of the engine. Checking should not be regarded as a routine operation, however. It should only be necessary when the valve gear has become noisy, after engine overhaul, or when trying to trace the cause of power loss. The clearances are checked as follows. The engine must be cold for the check to be accurate.

3 Apply the handbrake, then jack up the front of the car and support it on axle stands (see УJacking and Vehicle SupportФ). Remove the right-hand front roadwheel.

4 From underneath the front of the car, prise out the two retaining clips, and remove the plastic cover from the wing valance to gain access to the crankshaft sprocket bolt. Where necessary, unclip the coolant hoses from the bracket to improve access further.

5 The engine can now be turned over using a suitable socket and extension bar fitted to the crankshaft pulley bolt.

6 Remove the cylinder head cover as described in Section 4.

7 Draw the outline of the engine on a piece of paper, numbering the cylinders 1 to 4, with No 1 cylinder at the transmission end of the engine. Show the position of each valve, together with the specified valve clearance (see paragraph 11). Above each valve, draw two lines for noting (1) the actual clearance and (2) the amount of adjustment required (see illustration).

11.7 Example of valve shim thickness calculation
11.7 Example of valve shim thickness calculation

I Inlet
E Exhaust
1 Measured clearance
2 Difference between 1 and 3 3 Specified clearance
4 Thickness of original shim fitted 5 Thickness of new shim required

8 Turn the crankshaft until the inlet valve of No 1 cylinder (nearest the transmission end) is fully closed, with the tip of the cam facing directly away from the cam follower.

9 Using feeler blades, measure the clearance between the base of the cam and the follower (see illustration). Record the clearance on line (1).

11.9 Measuring a valve clearance using a feeler blade
11.9 Measuring a valve clearance using a feeler blade

10 Repeat the measurement for the other seven valves, turning the crankshaft as necessary so that the cam lobe in question is always facing directly away from the relevant follower.

11 Calculate the difference between each measured clearance and the desired value, and record it on line (2). Since the clearance is different for inlet and exhaust valves, make sure that you are aware which valve you are dealing with. The valve sequence from either end of the engine is:
Ex - In - In - Ex - Ex - In - In - Ex 12 If all the clearances are within tolerance, refit the cylinder head cover with reference to Section 4. Clip the coolant hoses into position (if removed) and refit the plastic cover to the wing valance. Refit the roadwheel, and lower the vehicle to the ground.

13 If any clearance measured is outside the specified tolerance, adjustment must be carried out as described in the following paragraphs.

Adjustment
16-valve models
14 See paragraph 1.

All other models
15 Remove the camshaft as described in Section 10.

16 Withdraw the first follower from the cylinder head, and recover the shim from the top of the valve stem. Note that the shim may stick to the inside of the follower as it is withdrawn. If this happens, take care not to allow it to drop out as the follower is removed.

Remove all traces of oil from the shim, and measure its thickness with a micrometer (see illustrations).

11.16a Lift out the follower and remove the shim (arrowed)
11.16a Lift out the follower and remove the shim (arrowed)

11.16b Using a micrometer to measure shim thickness
11.16b Using a micrometer to measure shim thickness

The shims usually carry thickness markings, but wear may have reduced the original thickness.

17 Refer to the clearance recorded for the valve concerned. If the clearance was more than that specified, the shim thickness must be increased by the difference recorded (2). If the clearance was less than that specified, the thickness of the shim must be decreased by the difference recorded (2).

18 Draw three more lines beneath each valve on the calculation paper, as shown in illustration 11.7. On line (4), note the measured thickness of the shim, then add or deduct the difference from line (2) to give the final shim thickness required on line (5).

19 Shims are available in thicknesses between 2.225 mm and 3.550 mm, in steps of 0.025 mm. Clean new shims before measuring or fitting them.

20 Repeat the procedure given in paragraphs 16 to 18 on the remaining valves, keeping each follower identified for position.

21 When reassembling, oil the shim, and fit it on the valve stem with the size marking face downwards. Oil the follower, and lower it onto the shim. Do not raise the follower after fitting, as the shim may become dislodged.

22 When all the followers are in position, complete with their shims, refit the camshaft as described in Section 10. Recheck the valve clearances before refitting the cylinder head cover.


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