Changing the head gasket on a car is a fairly long process, but can be done if care is taken to perform each step correctly.
This write up is a preliminary jotting of notes, intended to record the most important steps involved after recently having changed my friends head gasket on his EF Ford.
- Well equipped tool kit
- Torque Wrench
- Tube of UltraBlue Silicon
- Can of Hylomar
- New set of Gaskets
- New set of Headbolts
- Carby Cleaner
Empty the cooling system to a point lower than the head, probably a good idea to just drain it, as we will be flushing it later anyhow.
It might be easier to remove the thermo fans to get a little extra access to the front of the engine.
Unbolt, unclip, unhouse and otherwise remove anything connected to the head on the engine.
Remove the rocker cover.
For the rocker arm assembly, there are hydraulic lifters on the bottom of each arm, these lifters push the valve springs. They probably wont fall out of the rocker, but there is a possiblity of this. It is therefor a good idea to twist the rocker completely over so that the lifters easily rest inside the rocker arm.
There are 2 bolts per post to remove, something like 18 in total.
once unbolted, the rocker assembelly can be removed from the engine.
The timing assembelly can now be removed. Will need to get some more information about this, but there is a 17~mm bolt on the front of the timing gear which holds the cam shaft in place. Once removed, the cam shaft should freely lift out.
From here there are 14 head bolts which need to be removed. A breaker bar will be required, and care should be ensured to not strip/thread the bolts. These bolts can be thrown out, as they cannot be used again. This is because they are designed to stretch a little bit when they are torqued to the right specification, hence making them appropriate for single use only.
After removing the head bolts, the head can now finally be removed. When lifting the head, care should be taken to avoid the timing gear, and to ensure that the head is lifted vertically straight from the block. The chain tensioner is extremely fragile, and can snap extremely easily (as we learnt)!
Now that the head is removed, it should be sent to the machine shop for crack testing, milling, and inspection.
The block can now be prepared. This should be done with a scraper to remove any bits of gasket which have become stuck, and some wet-dry sandpaper.
You can take this time to clean up the rocker cover (inside and out), a little bit of petrol does a nice job of washing away any excess grease.
Once you get the head back from the shop, it is time to put everything together again. This is practically doing everything in reverse to pulling apart, ensuring to use new gaskets, and new head bolts.
The first step is to ensure that the block is totally clean and free of contaminants. Firstly, using a compressor fitted with an air gun, blow out the cylinders. Then, using some carby cleaner, and a nice lint free cloth, spray the cylinder walls and piston heads with cleaner, and wipe away any excess residue with the cloth.
For my friends car, there was a rubber gasket which sits around the edge of the timing chain housing. After inserting this rubber, squeeze a nice thick bead of ultrablue on top of the rubber, all the way around. Starting and finishing with a small blob at each end.
Next, cover the head gasket with a generous coating of Hylomar, on both sides, trying to keep it fairly even. This ensures that the gasket can obtain a good seal. Insert the guiding dowels into the block, and then carefully lay the gasket onto the block, lining up with the dowels.
The head can now be reunited with the block. This is much much easier with 2-3 people. Have a person on each side, and slowly lower the head onto the block. Its important that the head comes down vertically, and doesn't make much uneven contact with the block. Slowly lower the head, until the guiding dowels can be felt, it might take a little bit of a wiggle to get the head to match up perfectly, but when it does the head should slide on nicely past the guiding dowels.
The next job is to tighten the head bolts. This job isn't too difficult, you will need to know what torques are required for your particular head. Ours was 40nm, and then 90 degrees. There is also a certain order in which the bolts MUST be tightened. The two stages or torque must be completed one after another. That is, you do all of the bolts at one torque, and then go back and tighten to the final torque.
Place all of the bolts into the head, and do them up finger tight, ensure that you do not overtighten at this stage. Set the torque wrench to your desired torque (40nm for us), and torque the bolts, in sequence, to this torque. After this initial stage of torquing, the bolts (for our head), required a further 90 degrees. This means that the bolt must be turned a further 90 degrees. This can be done accurately with a degree wheel, or if none is available, by eye.
After the head is bolted in, the camshaft and timing gear can be reconnected. Place the camshaft into its position, and cover it with a generous amount of quality oil. Put the timing gear back on, and bolt in the chain tensioner.
The next job is to re-install the rocker gear. This job requires a little bit of delecacy to ensure the rocker assembelly is not damaged. Firstly place the rocker assembelly back into place, and finger tighten all of the bolts. It is very important not to simply tighten the bolts in any random order. You must start at the front or the back, and work your way in the same direction, slowly tightening the bolts with each pass. This is important because if you simply tighten the bolts in the middle first, the entire rocker assembelly will become bent.
After the rockers are back on, the rocker cover gasket can be fitted onto the rocker cover. Take care in placing the rocker cover onto the head, to ensure that the gasket remains in the correct position and maintains a good seal.
Finally re-attach all of the manifolds, hoses, cables, fans etc etc.
The cooling system should now be re-filled (or flushed).
Congratulations! Barring any major disasters, you are now complete! Close your eyes, hope for the best, have a suitable amount of fire fighting equipment near by, and crank your lovely engine over.