Removed the valve cover?
Change the gasket.
Fitted a camshaft?
Change the gasket.
PCV valve failed?
Change the gasket.
You get the idea... if you mess with the valve cover at any time; CHANGE THE GASKET.
![icon_twisted :icon_twisted:](./images/smilies/icon_twisted.gif)
Why is this gasket important and why should I change it?
The valve cover houses a magic little valve called a PCV [positive crankcase ventilation] valve. During an engine's stroke cycle, positive pressure is created in the crankcase (the area that houses the camshafts, tappets, valve springs, valve stems, etc.) and that positive pressure needs somewhere to go! If the PCV valve is not operating correctly, (i.e it has failed, there is no vacuum (due to a bad gasket!), or it's clogged) this pressure will take the easiest route out. Either via the spark plug shaft gaskets, or again, the valve cover gasket. It'll also drag some oil with it too!
When the gasket has failed; you have no vacuum; thus no PCV. It also means you piss oil all over your engine and lose lots of it. You know, oil, that stuff that lubricates your engine components and stops them from grinding each other to pieces? Yeah? Oil is important. Therefore, having a gasket to provide vacuum and a PCV valve that operates correctly is also important.
So how do I fit one correctly?
1) Remove the spark plug cover with a 10mm socket. Take out HT leads and place them aside - in order.
2) Remove the valve cover bolts with a 10mm socket.
3) Remove the 2 upper timing belt cover bolts (threaded through the offside of the valve cover) with, again, a 10mm socket.
4) Remove the valve cover. Easiest way to do this is by removing the oil filler cap, sticking your fingers in and giving it a tug.
5) Extract old gasket from the valve cover and dispose of it appropriately.
6) Remove the 3 half circle grommet inserts on each corner of the head (excluding where the camshaft sprocket is located). Place a screwdriver on their edge and press them out; they pop like Pringles.
7) Remove ALL residue of the old gasket; albeit on the engine head or valve cover*. Some GUNK or any old engine degreaser will do a fantastic job of this.
8) Place new half circle inserts into head - DO NOT FORCE THEM FLAT. Just enough to allow you to put the valve cover on.
9) Oil both faces of the gasket and insert into valve cover. A thin coat of silicone sealant or instant gasket can help if your head is slightly distorted/chipped or something. But only use such things if you need to.
10) Place the valve cover on the head and insert a bolt into each corner.
11) Tighten each corner very gently in an adjacent fashion (top right, then bottom left) until the valve cover and gasket are both mated. The half circle grommets will be fitted nice and snug too.
12) With the gasket mating the faces, now place the rest of the bolts in and tighten in, once again, an adjacent fashion. Once a bolt starts to get marginally tight, complete 1/4 of a turn and leave the bolt alone**.
*Don't use a screwdriver as this causes scratches, which are holes, which can cause leaks. Leaks are baaaaad.
**Failure to do so could cause you to crack the valve cover. Don't do it.