Citroen XM Forum

To get any trace of gasket off, use a sharp scraper. For the exterior use engine degreaser.

The really best solution s to take it to an engine remanufacturer and have them skim it to ensure flatness and they will wash it.

A window scraper is very good (plastic handle with a Stanley knife blade in it), for cleaning i use petrol, a paint brush cut down to make it stiffer and a new toothbrush, i usually pick a pack up from the £1 shop as they soften rather quickly in solvent.

D

Thanks chaps, that's great.

Gave the head a quick clean up this afternoon, so I could get a better idea of condition.
The little cups haven't rotated which is good, but they all seem to have a hair line crack, albeit not reaching the edges. Anything to be worried by?
I don't want chunks of metal falling into the engine! I hear it is quite common for these cracks to happen.




My main concern is this....


Pitting. To me quite serious. Not on the gasket face, but inbetween the valve heads. Again, is this something to be worried by, can it be fixed, is the head a rightoff already?!



Next and final amateur question is, if the head can be skimmed, is it best to take all the valves ect out first, or shall I leave them in then sort out them out later? My gut instinct is to leave it all assembled.

Hi Russ

Pitting like that is usually, wter getting into the cylinder over a long period of time or detonation, maybe just plain old corrosion, is this the seized pot that has the pitting?
Having said that so long as the valve seats have not been undercut at all i would leave it be, maybe just smooth it off to remove any sharp edges and potential hot spots but i don't do diesel so not sure if that is something that can cause an issue with pre-ignition or not.

The valves should come out before going to the shop, yes, in this case, they can probably skim it with them in due to the cam being removed but some shops will refuse to do it with the valves in situ regardless, that and you want them to be able to see the head and ports and they will let you know if there are any issues, if they can't see into the ports they won't spot any potential issues.
You have to pull the valves to reseat them and fit new stem seals anyway.
Keep them in order, make sure they all go back where they come from and use a light grade steel brush in a drill or similar to clean them up while the head is away being skimmed.

D

I can't see any cracks in the pre-chambers, any pics? Are you talking about the machined inserts between the valves?

The burning won't be pre-ignition as that's not possible on a diesel, but do look like errosion.

These heads can be skimmed with valves in, but if you intend to remove them anyway, it's best to do it first. You need to clean the carbon off to see what's going on and measure the flatness.

Thanks chaps. I shall remove the valves then. Knowing they are recessed, I wasn't quite sure about the best approach.
That's fine, I'll get on with that.

The corrosion is from the siezed pot. The others are absolutely spot on.

Yes Will, the little round machined inserts are what I am referring too. I'll get better pics of the cracks in the pre chambers tomorrow. They are very very fine.

Very fine pre-chamber cracks are common. The inserts are exactly that...inserts.

As well as skim the head, a good workshop will also clean and pressure test it.

More pics....

Cleaned up the corroded pot surface as much as I can.



Close up of each insert to see the cracks.









Everything apart from the valves and injectors is off now. Injectors are proving to be a complete s#*t to remove.
Valves are next. Hopefully tomorrow.