Knocking engine

My atmo GTA has developed a knocking noise from the top of the engine. My local garage man (not a Renault specialist) listened to it and said it was camshaft wear - he said that the PRV engine was prone to this.
I did a search on this forum and couldn't find any posts relating to camshaft wear, but when I searched the internet I did come up with comments about these engines being weak in that area. My engine has done a fairly big mileage - around 150K miles or possibly more as the speedo has been replaced (how unusual - not!).
My question is what is it that wears - do the camshafts run in plain bearings that can be replaced? If not what can be done to repair this? (Excuse my ignorance).
Thanks, Clive

Hi Clive. They're not prone to wear Early PRVs had problems with oil supply and the oil passages were widened very early on in production - this affexts only very early 2.6's.

Someone on here recently had a top end knock and IIRC it turned out to be a stuck valve.

I've seen problems with the oil jets getting blocked on a rocker arm which causes the rocker to wear and start to sound like an extremely bad tappet. NB the rocker arm shoe is softer than the cam lobe so can be replaced with no damage to the cam.

Clive, depends on what rockers your heads have been graced, most likely the later alloy ones with hard wear pads. These are far more wear resistant than the cast variety that Martin is most likely referring, and these are very hard to grind and so the wear will be in the cam lobes. Certainly from the atmo cams I have seen this has been the case. Conversely if you have the cast ones, then you would probably want to replace anyway.

As far as the bearings for the cam go, these run directly in the head and wear / clearance issues shouldn't be a problem even with a high mileage engine.

I would make sure your tappet clearances aren't now opened up, and set these back down first. The top of the valve stem gets beaten in with the impact and wiping action of the end of the follower adjuster, and the clearances gradually widen. Makes resetting with a feeler a real problem if it's well gone as the clearance is concave and the feeler gauge will rest on the margin of the stem instead. Have a look at the cam whilst you are at it, but provided you have a lobe left I would leave it The lift isn't that exciting on those cams, so performance penalty for some wear in the cam is not going to be that significant. The cost of changing cams isn't insignificant as it's a heads off job. Suggest having a look first…