All of this assumes the engine is in good condition, Alan makes a very valid point If the engine is out, take the opportunity to recondition it, its a relatively small cost as most parts are easily available plus its a great opportunity to inspect things more closely, find potential issues and learn new skills.
I wouldn’t recommend a head off procedure on an engine that’s been standing around unused or neglected for any period of time.
Robs advice for a digital camera or camera phone is excellent; I do this…..a picture is worth a thousand bits of fag packet.
Mikes recommendation re the alternative book “How to rebuild your” is golden, the Haynes manual is sadly lacking in certain areas, neither are without slight errors and omissions.
If the engine has been recently overhauled and requires a head off only procedure
here’s a few tips (not a definitive “how too”)
Don't get too hung up with the shiny link malarkey, just look for the dot on the outer diameter of the cam sprocket and mark the nearest link both on the sprocket and the chain (see below)
When making a chain wedge (there are internet templates around), the best thing is a piece of poly prop or nylon, if you don’t have that to hand use a bit of wood that doesn’t splinter or shed bits easily (you don’t want wood splinters in your oil ways)
On a stock cam sprocket engine, when the engine is a TDC there is a little “window” on the cam sprocket and through that you will see a notch on the back diameter of the sprocket and a “dash” mark on the cam retaining plate these two “match up” (approximately) depending on which sprocket location hole is used (Nissans mechanism to compensate for chain stretch) and the wear on the chain.
If you don’t disturb the cam/crank relationship when taking the head off then it should go back together fairly easily (that’s no excuse not to check things though).
Heres a "sort of" procedure
Rocker cover off, plugs out, battery disconnected and assuming all of the induction/exhaust is disconnected etc.
Take engine to TDC on the timing marks on the crank pulley (real TDC not the overlap cycle) so that the cam ears on cylinder 1 are up a la Mickey Mouse.
Note the notch and dash on the cam sprocket mentioned above (take photo)
Note which hole the cam sprocket location dowel is using (take photo)
Look for a dot on the outer diameter of the sprocket and use a paint blob/tippex/scribed line to identify the chain link nearest it (take photo)
You can make a piston lock (old spark plug with a radiused end jacking bolt going through it) this can help prevent engine movement and reference TDC.
Put your chain wedge down in between the rising and falling links, make sure it is very well seated and pushed home as this is the most important thing you will do (make sure you have a mechanism for retrieval such as the coat hanger mentioned)
Once all is secured (check again that the chain wedge is securely fitted as you only get one shot at this), remove cam sprocket bolt whilst using a large spanner on the “ears” on the cam shaft body” to prevent any rotational movement of the cam (less work later on to re-align everything)
Remove the cam sprocket from the nose of the cam, it should come off fairly easily, a soft mallet and a light tap may be needed.
Drop the chain down into the large oil way at the front of the head, it can’t go to far, the chain wedge stops it. You need to be able to get the chain back out once you put the head back on, I use a magnetic retrieval tool, string works just as well.
Get some ultra clean rag and use it to cover this large gap up, its not uncommon for all manner of bits to drop in here, if that happens then you will definitely be taking the front cover off.