I did the tappets today and although they weren't miles out (as I'd hoped), odd ones were out of tolerance and needed adjustment. I haven't had a chance to do a road test yet so whether or not it has made any difference is a moot point.
I can't be sure of this but, judging by the state of the nuts and bolts I removed, my suspicion is that the inlet manifold and cylinder head cover had never been removed before today - despite four main agent stamps in the service book.
My tips for anyone thinking of doing the tappets themselves are:
1. Set aside a whole day as there's a lot of dismantling and reassembly involved. Take your time and don't rush. It took me between four and five hours to complete the job.
2. I used a 1/4" drive socket set (10mm and 12 mm sockets plus extension bars and ratchet handle) to remove and re tighten all the nuts and bolts. I don't think anything larger would fit as access is restricted to the manifold/EGR plate fixings in particular.
3. You will need some silicone sealant for the timing cover to engine block joint. Check yours hasn't dried up in the tube before you start. Mine had.
4. I tried turning the crankshaft with a 19mm spanner as recommended in the Haynes book but unless you have access from below, there isn't really enough space between the engine and the inner wing to get access. Instead, I put the car in gear and pushed it to turn the engine and this worked fine. You will need an electric torch to see the markings on the camshaft gear wheel and to locate out-of-the-way bits and pieces.
5. Get yourself one of those devices with spring operated claws for picking up any nuts and bolts that you drop. I needed it a few times and I was trying to be careful. I also found this tool very useful for holding the manifold bolts and studs when I replaced them. It even enabled me to turn them in by hand before tightening with the socket.
That's about it. The job itself is not so much difficult as fiddly but whether or not it is 'necessary' every 25,000 miles, I'm still undecided.
