The main special tool you need is the special socket to undo the cylinder head bolts - there's another recent thread on here that talks about the tool you need.

The cams are held in using 12 point bolts - if you only have 6 point sockets, you might struggle.

You'll need to rig something up to remove the guide rail pins - I used some M6 studding and some washers and tubing to pull the pins out. I took the opportunity to replace the chain guide.

The chain is tensioned using a hydraulic tensioner that's on the left hand front of the engine. You'll need a large spanner or socket to get this off. I used a vice to squeeze the old oil out of the tensioner, and a valve spring compressor and a baked bean tin full of new oil to get the new oil in - the method is described in the manual.

I was quite paranoid about dropping things into the void where the timing chain runs - there are a couple of smaller bolts between the head and block down there.

Tie-wrapping the cam sprocket will work well. I also removed the vacuum pump, and wedged the chain against the injector pump sprocket. But, the guides run so close, it's difficult to imagine the chain coming off.

There's a measurement procedure given in the manual to allow you to check if you need new head bolts - typically, if the head hasn't been off before, they'll be OK to re-use.

When you have the head off, I would recommend that you check all of the onlet valve head heights. On my OM606, the inlet valves on the rear cylinders had sunk - to the extent that they weren't sealing. This is what motivated me to remove the head in the first place.

I did mine in April 2007, and in the interim, there have been a couple of people on here who seem to have the same valve problem - it's worth checking. While the head's off, putting a couple of new seats in isn't a large extra expense if they have sunk a bit.

You'll needa set of injector pipe clips, they're really brittle. Don't think of not replacing them if they fail - your injector pipes will fail from fatigue in short order. If your engine doesn't have a turbo, you may find that you need to damage the rubber/plastic crankcase ventilation ports in the inlet manifold, and so, it's worth ordering a set of these before you need them. Also, as you'll disturb all the thin leak off pipes from the inkectors, it's best to fit new ones.

It's an excellent opportunity to check the condition of the engine wiring harness. I found mine was badly deteriorated, and I've now got a new one to fit, which I'll be doing sometime over the next few days.