HP Pump - Stripdown and Overhaul

One of the hardest working components on the DS must surely be the high pressure pump (The HP Pump).

After......

It is, after all, the heart of the car. The reason your 'cycle time' drops and your pressure regulator clicks in every few seconds, is due to a loss of pressure in the system: leakage past seals and worn valves and pistons. Two of the main culprits are the steering rack and the HP pump. With the engine all out, now is the time for a strip and rebuild. My car is a BVH so has the seven piston pump with a three groove pulley. It was in need of a good overhaul:  

Before......My HP Pump - 11 September 2015

The stripdown for the seven piston pump is covered by Operation DX. 391-3 in Section 2 of volume 2 of Manual 814.

You can also find a series of four very handy videos on Youtube from the ever-reliable "DSSMPassion" people. Here's a link to the first one:

Hydraulic Pump strip down video

DSSMPassion also have a couple of videos on testing the pump - but I don't have the kit available to be able to follow their example.

Finally, I also found this very good article on the web:

Pump Overhaul Instructions.

I bought a rebuild kit for the HP pump. This consists of 18 (that's eighteen) 'O' rings of various sizes. All will get used. If you find the thought of a job that is going to involve the parts and work associated with 18 'O' rings daunting, then give this job a miss!

The first thing to say about this HP Pump rebuild is that it gave me a lovely clean pump with new seals - but won't have addressed any issues down to piston wear. if you want to deal with that, you need to source a refurbished, pressure-balanced pump from 'Citrotech' - but they're not cheap......Currently €445.

First I removed the pulley. As well as the lockwasher, there is a small key on the shaft. Easy to lose (though you can buy replacements from Der Franzose for example).

After removing the pulley, the next job was to remove the pump cover - the bell shaped dome that covers the inner workings. There is a special Citroen tool for this job - but I've never seen one.

I carefully noted the position of the triangular brackets on the cast iron front end plate as I removed them. As a bvh car, my car has two brackets: one holds the tie bar to the water pump, the other holds the tie bar to the centrifugal regulator. The bolts are M8 size BUT, have a fine 1.00mm pitch thread.

I Noted the Positions of the Triangular Brackets

There were also plain flat washers under these two brackets and the single nut - but not the other two bolts. Also note the difference heads on the bolts - more about that later......

Washers Under the Brackets

I marked the relative position of the pump cover to the front end plate with a scribe so that I could put it back in the same position when re-assembling. 

I removed the 'closing cup cover' from the bearing by getting a knife then screwdriver blade under the edge and working it loose. Underneath is a flat spacer (the 'pump deflector') and an 'O' ring.

To remove the pump cover I followed the suggestion in the "overhaul instructions' (link is above) and rigged up a press. I bought 200mm length M8 bolts with long, plain shanks. Actually these were 'threaded eyes" like this:

These tend to have a 1.25mm pitch thread as supplied - too big to fit into the HP pump body. It's important that the full length is not threaded as, once the eyes were removed, I cut 1.0mm pitch threads on the remaining plain shanks. The threads were not perfect as the bolt shaft was slightly under-sized, but I was able to cut strong enough threads for the job in hand. I ended up with three rods: 8mm x 1.00 pitch at one end and 8mm x 1.25mm pitch at the other.....

Choosing the 'best' three holes in the front end plate, I fixed my rods - then made a backing plate with a sturdy block of wood - remembering to cut a hole where the pump spindle would need to pass through.

I found a couple of off-cuts of angle profile and used these as spacers and to press down on the edge of the pump cover as the 8mm bolts were tightened.

With the mounting point of the pumps front end plate clamped in vice, I gradually tightened each of the three bolts in turn. As the block of wood was drawn towards the pump, the angle iron spacers pushed the pump cover off.

Gradually...........it gave up what was within.

All very satisfying.

This is what I found inside:

Loads of thick black goo!

There is clearly a lot going on inside the pump. Here is a very short video that shows one in action......

Action of the High Pressure pump

And a rather hypnotic animation......

HP Pump Animation

Next job was to separate the bearing spindle from the end plate and pump body. This is done by pushing the spindle out. The spindle already has a dimple in the end to locate a puller. WARNING: do not fully remove the spindle so as to fully disengage the piston push rods from the swash plate as all the springs, push rods and pistons will fall out and get lost or - equally as bad - get muddled up.......

With the spindle head just pushed through enough to allow access, I numbered up each of the piston locations and carefully removed each push rod, piston, cap and spring set in turn. Citroen use a special aluminium rack for storing all the removed parts and even provide instructions for making one: Special Tool MR.630.42/6:

I was feeling pretty confident so made my own:

Eventually I put the matched parts in numbered tubs. Technically it's only the pairing of each piston and cylinder (and their location in the aluminium pump body) that needs to be maintained - but I found it just as easy to keep all the groups of little bits together. 

The spindle/ swash plate/ bearing combo was then finally removed from the pump body. There is an olive that sits in a gap on the swash plate and which slides up and down a locating stem on the pump body. The olive was recovered and kept safe.

With all six bolts and the nut removed from the front end plate, the aluminium pump body was removed. Mine came away leaving the castellated distance pieces stubbornly stuck to the pump end plate - but it was only compressed 'O' rings that were keeping them there.

Castellated Distance Piece on Front End Plate

In the castellated top of each distance piece is a small flat circular valve disc. Once removed, underneath each one is a small spring and the stubborn, sticky 'O' ring.

'O' ring, Distance Piece, Spring and Valve Disc

The aluminium pump body held the seven piston cylinders. These were simply pushed out and freed - though there is an 'O' ring lurking in a recess at the bottom of each bore of the aluminium body that needs to be winkled out.

All these parts were left to soak in pots of 'Mek' for a while before being given a careful clean up with a tooth brush and then a liberal soaking in LHM to stop any rust or corrosion, before being returned to their designated tubs. I took each small valve disc and, using some oiled wet and dry paper on a sheet of glass, carefully lapped each side on the flat surface to make sure it was 'true'.  

Parts sorted - and individual washing containers to boot!

I struggled to remove the nut from the end of the pump spindle to then allow me to remove and clean the bearing race. Firstly the little tab is very brittle and broke off as soon as I bent it. It was there for a reason - so that was a worry..... 

The Locking Tab on the Nut Broke Off.....

Secondly, and even with the tab gone, it took considerable force to loosen the nut. 

Before I loosened it too much, I readied myself to capture all the ball bearings that I knew would fall out. 

Outer race, bearing cage and balls

Intermediate bearing race and spacer

I also removed the ring/ cage retaining the smaller ball bearings. This was a bit tricky and I had to be careful not to distort the cage as I pulled it off.

Cage for the inner race

All the parts were laid out for cleaning and polishing.

If you want to do a thorough job (and not have any 'O' rings left at the end of this!) then the big bearing in the pump end plate needs to come out...... 

With the pump spindle removed, the bearing can be drifted out from the end plate. Underneath the bearing is a brass distance piece (a 'seal carrier') that holds an 'O' ring -  and beneath that a spring.

Seal Carrier Distance Piece

Seal carrier, spring and bearing

I soaked the bearing in 'Mek' to loosen up and remove all the old grease....... 

........before re-packing it using a syringe.

The video from DSSMPassion shows a part-re-assembled pump being spun with an electric drill in order to re-pack the bearing. I wasn't keen on the idea of running my delicate HP pump dry, so instead rigged up a way to spin the bearing before re-assembly - I carefully rigged up a shaft through the bearing inner and, gently clamping the bearing outer in a vice, attached the shaft to my drill and gave it a spin. I then re-packed the grease at several more points during re-assembly.

I degreased the cast pump end plate and treated it for any rust - being careful to avoid getting harsh chemicals in the hydraulic passageway or on the pin roller bearing that remained in the body. I gave this bearing a flush out with 'Mek' to degrease it and remove any contaminants, then used compressed air to blow everything away, before re-lubricating it with LHM.

I pushed out the 'olive' stem from the aluminium pump body and gave the body a close inspection. These have a habit of developing cracks on the thin parts between the bores for each piston/ cylinder. If you do find problems, it's possible to get replacements manufactured from steel. I've also seen alloy replacements on sale. I cleaned off all the crud from the circumference and, using some oiled wet and dry paper on a sheet of glass, carefully lapped each flat surface to make sure it was 'true'. I soaked it in 'Mek' for a while before giving each bore a good clean out with a tooth brush and cotton bud.

I began re-assembly: the 'olive' stem was pressed back into the aluminium pump body which was then laid flat in my vice. 

All The Parts Were Laid Out In Order - and the 18 'O rings.....

Honouring the numbering order established when I took the pump apart, I gradually replaced each part - giving each a generous soak in LHM as I did so. First were the bigger 'O' rings in the recess at the bottom of each cylinder bore, followed by each cylinder itself. It is important that these are pushed home fully. They should almost 'click' as they lock into place. Then came the small valve discs and the castellated distance pieces. The small valve discs have to be placed centrally so that the castellated distance pieces sit around them and flat. 

Castellated Spacers Fit Over And Around The Discs on the Cylinders

If reassembly has gone as planned, the castellated distance pieces should be slightly recessed (about 1.5mm?) in each bore - thereby leaving a locating 'lip' for the slightly smaller 'O' rings. 

The Cylinder In The Middle is Correctly Recessed In It's Seat

If there is no recess, it means that either the cylinder did not 'click' into place, or the castellated distance piece is sitting on top of the disk. Or both! Lastly (for this stage) the smaller 'O' rings were located in the recesses, before the front end piece (with new 'O' ring) was lowered on to secure the 'sandwich' and I prepared to bolt up.

I noticed that some of the six bolts were different. Two had dimples on the end, but the four that did not were slightly longer. These longer ones were the four bolts used to secure the brackets and used in combination with washers. Presumably the extra bolt length was compensate for the thickness of the washers.

Bolts for the brackets vary in length

When I had taken it apart, I had removed flat washers from under the nut and the four bolts that secure the triangular brackets.

The re-assembly instructions in Op. DX. 391-3 were clear that serrated washers should be used on re-assembly, and the photos showed serrated washers also used even where there had been no flat washers. The puzzling thing is that the serrated washers go underneath the triangular brackets. I had expected they would go on top - between the brackets and the securing bolts? No matter: I dutifully went ahead and used serrated and in the locations expected.  Bolts were torqued to 3.5 mkg (34Nm or 25ft.lbs). That's quite hefty!

I turned my attention to replacing the bearing and seal carrier with spring underneath. In the DSSMPassion video, the seal carrier, with new 'O' ring, is pressed down and holds back the force of the spring - allowing the bearing to be refitted over the top. 

Don't you believe it! With a liberal application of LHM, the spring kept forcing the seal carrier back up and out. In the end I lined up the spring and seal carrier and then started to press the bearing back into place. Once the bearing had started to locate, it began to compress the seal carrier and spring - holding them steady. I put my finger in the pin roller end of the shaft and re-centred the sealing plate over it's locating hole. I pressed the bearing in a little further and adjusted the seal plate position again. I did this several times  until I was confident that the bearing would now press the bush into it's correct location. So that I did not bend the threaded parts of the triangular brackets as I tightened my vice, I used a large socket (approximately the same size as the outer ring of the bearing) as a spacer to finish pushing the bearing home - just flush with the surface of it's recess.

As, after fitting, the pulley hides much of the end of the pump, I took the opportunity to paint up the re-assembled body - being careful to mask the pump area and shaft. I also part-painted the outer edge of the aluminium pump body - nearly as far as the recess that holds the 'O' ring that seals the cover on. 

I will give it all a final coat of paint once it's assembled.

Back to the spindle and pump assembly. Using the securing cage as a 'cup', the small ball bearings were doused in LHM which helped glue them in place. I lowered the spindle down and over the cage -  just enough to stop the balls falling out. With a bit of careful teasing I was able to relocate the balls in their track - at which point the cage then held it all together and i was able to turn the assembly over. 

The bigger ball bearings were far easier as they sit in the groove on the swash plate and are held in place by the nylon collar. 

Everything was sandwiched up and generously brushed with LHM.

I finally got back to that troublesome nut - the one with the tab that broke off. My plan had been to over-tighten it slightly then bend over the edge of the nut in lieu of the tab, but try as I might I couldn't get it to tighten beyond the tab alignment point. Instead I used a good dose of thread lock and tried to peen the broken edge of the tab over. Other than that it's going to have to be fingers crossed.......

Back to the pump body...... Still honouring the locations from which they were removed, the spring, piston, cap and push rods were located into each of the relevant pump cylinders.

Spring, Piston and Cap - all doused in LHM

In each case the pistons were coated with LHM and I checked that each moved freely in their cylinders.

I lowered the pump shaft onto the body/ piston assembly and made sure that the push rods were located in the recesses in the swash plate. I refitted the olive. 

If you look carefully  on top of the shaft there is the recess where the (broken) tab locates, but also a small circular hole. Although it looks to be off centre, allowing for the bend in the shaft it is centred on the spindle and is the end of a passage to carry LHM. it also serves to locate a puller or pusher...

The round hole in the top served as a 'centre' for the puller

The legs of the puller were located in the grove of the aluminium pump body where the large 'O' ring will go.

With everything now lined up I clamped it in a vice and used the puller to carefully push the shaft back onto the pump body and bearing a bit at a time. 

Puller legs were located in the groove of the aluminium body

Checking to make sure that the piston push rods were still correctly located in the swashplate and not bending, I slowly pushed the spindle back on to the pump. It went on very easily. The reason is that the bearing was being pushed out the other side!

The spindle pushed the bearing out the other side.....

With the puller still attached, I used a large socket (again) to drift the bearing back into position. I wound the puller again - pushing the bearing out once again, and drifted it back into position again....After several cycles like this, the shaft was fully home and the bearing was back flush within it's recess.

Despite what I wrote earlier, I will admit that I could not resist connecting a drill up to the shaft and giving the pump a few low speed rotations. This was more about checking the pumps free movement rather than bedding in the bearing grease and before and after doing this I applied LHM to each cylinder for added lubrication. I gave the bearing a final loading with grease before adding the sealing 'O' ring, deflector plate and closing cup/ dust shield.

One last check that the bearing was loaded with grease.....

With the last 'O' ring fitted around the aluminium pump body and coated in LHM, I lined up the marks I had made earlier on the pump housing to make sure it was in the right orientation, then used my vice to carefully push it back on to the pump. It should push on and leave about 2mm to 3mm of the aluminium body visible all the way around it's outer edge. With that done I gave the whole thing another coat of paint. 

I used glass beads in my blasting cabinet to clean up the pulley wheel and started to paint it up - but ran out of paint!!! 

HP Pump: Reassembled and Painted. No Pulley....

Finally finished: