Citroen XM Forum

Maybe the clearance volume was increased by those changes to the PRV engine and the compression ratio dropped a bit? But that would have dropped power a little so they must have had a good reason for bothering to do that.

Exhaust valves sharing the same cam lobe is a bit naff, asking for trouble I would have thought. What did they do to rectify that? The 12 valve V6 in the SM has 4 camshafts and one lobe per valve. The big valve 3 litre SS version made 220bhp when it came out in 1975 and that's on carbs!

Yea, the PRV 24v was STILL a single cam per head, but the cure was to fit Ceramic Lifters to the head instead, which DID cure the issue and sorted them out.

Not sure if they also changed the Cam Shaft either.

I just came across this set of photos - might help when you take your spare engine to pieces.

http://rammstein.dfmk.hu/~phoenix/XM-PRV-V624vRebuild/

Yea seen those impressive sets before.

The buggered engine of course is already on my shed floor out of a car so not a majour issue.