Further to my post above, this is information that I gleaned from the Citroen forum.
Service Action
Check of the noise coming from the camshaft drive chain.
Identification of the type of camshaft drive chain fitted to the internal combustion engine.
Replacement of the camshaft drive chain with an 8 mm chain (Modernisation of the internal combustion engine ).
Engine management ECU downloading (if necessary).
Parts required
1Camshaft kit (Part No. 16 381 598 80).
1 Camshaft pulley bolt (Part No. 0806 49).
1 Crankshaft pulley bolt (Part No. 0516 A3).
1 Camshaft seal (Part No. 98 239 200 80).
1 Seal (Part No. 3111 27).
1 Timing belt kit with coolant pump (Part No. 16 289 261 80).
1 Injection pump outlet pipe (Part No. 98 162 963 80).
1 Cylinder 1 injector supply pipe (Part No. 98 117 373 80).
1 Cylinder 1 injector supply pipe (Part No. 98 117 375 80).
1 Cylinder 1 injector supply pipe (Part No. 98 117 376 80).
1 Cylinder 1 injector supply pipe (Part No. 98 256 155 80).
4 Injector seals (Part No. 98 042 205 80).
4 Clamp fixing bolts (Part No. 98 089 827 80).
1 Set of oil separator seals (Part No. 16 381 593 80).
1 Set of vacuum pump seals (Part No. 4556 24).
4 Injector well seals (Part No. 98 173 808 80).
1 Air union seal (Part No. 98 137 583 80).
1 Diesel injector return pipe (Part No. 98 247 231 80).
1 Oil filter (Part No. 16 806 824 80).
N.B. : To optimise logistics, the parts kit available contains the camshafts, the camshaft carrier, the chain, the tensioner and an information label to be affixed in the engine compartment
Check
The engine coolant temperature must be higher than 80 °C.
Engine running at idle.
Check if there is a knocking noise in the upper area of the cylinder head on the timing belt side.
If there is a noise: Continue the check.
Identify the type of camshaft drive chain fitted to the internal combustion engine.
Locate and note the part number engraved on the camshaft carrier (1) (at "a") using a mirror .
If the part number is 9812647280: The internal combustion engine is fitted with a 7 mm camshaft drive chain: Carry out repair .
If the part number is 9830580480: The internal combustion engine is fitted with a 8 mm camshaft drive chain: The internal combustion engine has been modernised: Do not apply this document; Carry out in-depth fault finding.
N.B. : If the camshaft drive chain is noisy and the internal combustion engine is fitted with an 8 mm camshaft drive chain, send a dealer issue detection incident (DID I)
Repair
Remove the camshaft carrier (1).
Additional parts which must always be replaced: None.
In addition, carrying out this repair requires the following operations to be carried out:
Observe the safety and cleanliness recommendations
Use the products recommended by the manufacturer
Perform the operations that are required prior to a disconnection of the ancillaries battery
Remove the under-engine protector
Remove the scuttle panel
Remove the air filter housing
Remove the windscreen wiper arms
Remove the timing belt
Remove the air mixer unit
Remove the vacuum pump
Remove the camshaft position sensor
Remove the 4 Diesel injectors
Remove the fuel high pressure common rail
Respect the safety and cleanliness recommendations that are specific to high pressure Diesel injection (HDi) engines
Modernise the internal combustion engine by replacing the camshaft drive chain with an 8 mm chain.
Replace the following components :
The camshaft chain
The hydraulic tensioner
The exhaust camshaft
The inlet camshaft
The camshaft carrier
The coolant pump
The timing belt kit
Fit the new camshaft carrier (1).
Additional parts which must always be replaced :
4 Diesel injector seal
1 Camshaft pulley bolt
In addition, carrying out this repair requires the following operations to be carried out :
Observe the tightening torques
Apply a bead of sealing paste of about 1,5 - 2,5 mm diameter around the seal face ( Index "E10" )
Refit the fuel high pressure common rail
Refit the 4 Diesel injectors
Refit the camshaft position sensor
Refit the vacuum pump
Refit the air metering unit
Refit the timing belt
Refit the air filter housing
Refit the under-engine protector
Perform the operations that are required following a reconnection of the ancillaries battery
Bleed and top up the level of the cooling circuit.
N.B.: A label supplied with the camshaft kit must be affixed in the engine compartment; this label indicates that the engine has been modernised and the mileage of the next timing belt replacement (in 180 000 km or 120 000 miles or 10 years)