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Bosch Injection Pump Distributor Head Seal Replacement


This has some tricky bits as well...

Please proceed with caution with this task. It is easy to snap the distributor shaft/HP Pump plunger if the head is not lifted dead square. If this breaks the pump is toast!

This seal is a large O ring that seals the Distributor Head/ HP Pump assembly to the main pump body. It can leak badly and cause air ingress and consequent starting difficulties.

My apologies for the quality of some of the pictures. I will replace them shortly.

Rotate the pump so that it is between compressions (i.e. shaft free to turn a little)

Mount the pump in a strong vice with the rotor head upwards. This is vital. Seal the injector nozzles. I have some caps for this. Drain the pump whilst in this position by allowing diesel to leak from the fuel inlet union. DO NOT ATTEMPT THIS JOB unless the pump can be securely held in this manner. Failing a vice, a CLEAN "Workmate" will do. If the head is removed with the pump lying flat, a whole pile of springs, shims and washers will fall out in a disorganised heap!

Normal clinical cleanliness rules apply.

Remove the 12mm bolt in the middle of the rotor head. This is the timing access hole. If you do not remove this bolt to let air in, the rotor head will hydraulically lock to the shaft.

Remove the immobiliser module (if fitted) Immobiliser Removal and disconnect the Stop Solenoid wiring.

Remove the framework around the rotor head. Some of this framework is secured by rotor head mounting bolts. Only remove one at a time and replace it as soon as you can with a nut underneath to act as a spacer. The bolts will be too long otherwise. At least two rotor head bolts must be in place at all times (at a diagonal) to prevent possible snapping of the distributor shaft.

When the framework is off, carefully loosen each rotor head bolt gradually and equally a turn at a time. There are two very strong springs under the rotor head and as you loosen the bolts, these springs will cause the head to rise. It MUST rise squarely and gently. If the head is allowed to tilt off-square you risk snapping the distributor shaft.

A point will come when all four bolts are loose and the head will have risen about 8mm. Remove the bolts completely.

Carefully and squarely, lift off the rotor head, gently tilting it slightly sideways toward the pump top. Beware of two small springs that will fall into the pump internals. You may find the fuel delivery metering ring on the distributor shaft will come adrift from the dowel that secures it to the throttle plate. Do not worry, it is easy to re-engage on reassembly.

If the head is reluctant to easily lift, pass a small (clean) drift down the timing hole and exert gentle downward pressure on the end of the shaft as you lift the head up.

These are the springs:

Do not touch anything beyond this. Replace the seal and reassemble. Generally, the reassembly is a reversal of disassembly but those two small springs will need holding in place with grease so they do not fall out as you place the head back on. Ensure the fuel delivery metering ring is engaged on the throttle plate dowel. To ensure the ring stays put, replace the head with slight sideways pressure toward the pump top. Lubricate the shaft and hole in the distributor head with thin oil (Citroen LHM is ideal)

If it does not seem to be going back together easily and sweetly STOP and recheck everything is correctly located, particularly the metering ring and the two big springs. If still unhappy, check the shim (last picture) is in place under the distributor shaft. It may have jumped out of its recess during disassembly.

Ensure the spigots of the two big springs engage in the holes in the head correctly. Tighten down the rotor evenly in a diagonal fashion as you would a cylinder head.

Here are some internal shots:

And a layout of the major parts just in case. Observe the shim between the shaft and pump plate.


Page last updated 4 October 2008


The End, Job Done!...