My Citroen XM 3.0 PR-Vestige

[Dean]

Its just no good when your being nagged on an automotive forum to finish the bathroom aswell

Next step is to get the other head off, gearbox off, make a stand and order the etch primer/paint. Then its get the assorted wire cup brushes and sander out and get cleaning, degunking and polishing, there is lots to do! got another little fabrication job to do while im making the stand up too.

Taste of things to come
photo(55) by Deanxm, on Flickr

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[citroenxm]

Ooo nice one dean the gaskets arrived....

[russ92xmsed]

Has Santa been early? Very good haul!

[Dean]

Thts one advantage of getting older, Santa comes when required!

I dropped the cylinder head today and all the valves and camshaft fell out, the gasket faces cleaned up too.

Slight concern has been raised over the large inlet valves, the retainer collets are not the best design and locate on one groove in the valve stem, this is compared to 3 grooves in the XU engine. The issue is the collets are a very sloppy fit and the valves themselves will not come out of the guides, i think the weight of these larger valves and the spring loading on the single groove for the retainer collets has elongated and burred/flared the end of the valve stem, very weak design.

Also on a side note the intake looks like it flows well, nice matching port sizes and large ports, the exhaust ports howver are just shocking, the machinng is awefull, the valve seats are half hanging out of the head on one side and are nowhere are not machined at all, they are way smaller than the exhaust header size too and the valve looks half the size of the intake so i would of thought they could of dressed the ports up a bit. Could be why this V6 makes about 5-10hp less per cylinder than the XU 2.0, frictional losses aside..........

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[russ92xmsed]

and not a lump of coal in sight! Very lucky! ... wish santa would deliver a leather single spoke!

That's amazing. So can you clean all that up to gain some extra power?

Pity about the little accident. That's annoying too as don't you need to keep the valves in some sort of order, or if your lapping them in does it matter?

[Dieselman]

Valves can be swapped round at will as lapping will reseat them.

[Dean]

The valves will need to stay matched to their guides still in an ideal world but lapping will make them seal, "dropped" is the only way they must have come out, i wasnt working on it.........
Cleaning starts
photo(56) by Deanxm, on Flickr
Inlet port view (nice)
photo(62) by Deanxm, on Flickr
Exhaust port view (poor effort)
photo(58) by Deanxm, on Flickr
So far as freeing up flow in the exhaust goes im not sure, in the picture above you can see the stepped ridge behind the valve seat, i may be able to open this up and smooth it in but this is material the valve seat is set against and i dont want to weaken it, the main issue is the shape of the port around the valve guid, its like a flat ceiling parallel to the valve seat and whatever you do it just a bad shape, i can open up the port at the mating face of the manifold to match the sizes but i need to increase port diameter by 7mm to do this and most of the restriction is exhaust valve size, the square flat wall behind the valve and the 90 degree turn the port must make, it will make me feel better though and im sure with such a massive restriction there is better flow to be had, i would guess if you could free up half a horse per cylinder with 6 cylinders there is scope for improvement.
Movement in collet shown with right collet held in place and left collet moved all the way down, i did get them out in the end by carefully cleaning the collet seating area with fine wet and dry to remove the burr, not sure if i want to put those inlet valves back in though......2.0i ones are a smaller diameter by a few mm so they cant be swapped either.
photo(60) by Deanxm, on Flickr
And all the way up
photo(61) by Deanxm, on Flickr
Camshaft
photo(59) by Deanxm, on Flickr

[Dean]

I think the following photo will highlight my concerns over the exhaust ports on the 12v V6, the inlet is smooth and well designed, all ports are mached in size and look like they flow ok, or should i say they visually 'flow' well.
The following picture shows the exhaust gasket against the exhaust ports, the holes in the gasket ar exactly 2mm larger (when the gasket is placed against the manifold just 1mm of the manifold face shows inside of the gasket sealing ring) than the manifold which although filled with casting chaf is actually very nice and open and flowing for an OE cast manifold.
But look at that horrific size difference between what is basically the manifold ports and the head port sizes, im no engine builder/tuner but i have tinkered with a few engines in my time and ive not seen anything like this.
photo(63) by Deanxm, on Flickr

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[Dean]

just to be clear the port in the head tapers down as it moves towards the gasket mating surface, the manifold is then larger, anyone know why it would do this? am i missing something?

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[Dean]

Well after doing some research last night and reading up about people who make it their business to tune the PRV engine plus a quick call to Fred the head i have come to the decision that i will take out the hour glass shape of the port which would mean opening it out by about 3mm diameter to about 15mm depth and call it a day.
There are a few water ways close by to the port and a lot of the undesireable structure seems rather structural unfortunately, opening up does produce very good gains but there is risk of hitting porous structure and weaking the head which can cause failure in extreme case, also distortion of the valve seat if im reading right.
An gains would be at the top end of the rev range anyway and im not going down the route of a massive change to the exhaust so its just onward with the cleaning, i mean bathroom.

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