DV20 Head Gasket
If you need to replace the head gasket these steps will help you.
Firstly do what you can to drain down the cooling system. If you have a vacuum extraction pump you may be able to extract the water from the T pipe behind the flywheel.
Remove the rocker cover. Undo the oil feed banjo on the side of the rocker bracket. Remove the plastic hose which goes to the air filter intake. Remove the rocker bracket by undoing it's two retaining nuts. You should now be able to lift the rocker bracket from the head. You can now remove the valve rods which must be labelled so they go back in the same order.
Undo the the head nuts. The nuts should be undone in pairs. So looking at the engine head from the flywheel undo top left and bottom right, top right and bottom left. Do the same with the 4 inner bolts leaving the central one till last.
Once you have undone the the nuts and removed the washers put them on a piece of paper so they remain in the same sequence and can be replaced in the same order when you come to re-assemble the head.
The engine block.
And the cylinder Head. The grey material on both is the remains of the old head gasket. This must be completely removed by scraping with a piece of plastic. An old credit card works very well. Do not be tempted into using anything like a screwdriver of a chisel. You may damage the mating surface which would prevent a proper seal.
Before you start scraping the engine block put some rag or kitchen roll into the gantry on the right to prevent as much debris as possible from entering the sump. Once you have removed as much as you can by scraping it's necessary to continue with abrasives to get both head and block back to bright metal.
This is absolutely essential. Head gaskets cannot be re-used so you only have one shot at it. Any remaining material may prevent a proper seal from being formed.
I used and old credit card to scrape away most of the old gasket. Then wiped it down with white spirit and used fine steel wool to get back to reasonably bright metal. If you do use steel wool you can use a magnet to retrieve any debris.