The four cylinder L-series motors are durable, bullet-proof motors, but their biggest shortcoming is their ease of blowing head gaskets. If you suspect that you have a blown head gasket (i.e. steamy exhaust, disappearing antifreeze or milky oil) you should at least attempt to retorque the head before committing to changing the gasket.

Before starting on either retorquing the head or head gasket replacement, you want to make sure you have a COLD engine. Let it sit overnight. Start by removing all the spark plugs.

Retorquing the Head

Loosen ONE bolt at a time. Start in the order you would normally torque them, from the middle working outward. (If you are planning on removing the head, you loosen from the outside, working in toward the center).

After you break ONE bolt loose... I like to remove it, and inspect the threads. Clean threads means no coolant has been seeping into the bolt holes. Rust/dirt will mean you can not get as accurate of a reading when it comes time to torque it. Wire brushing the bolt clean, before reinstalling it, is a good idea. Torque the head bolt. I like using a beam type wrench, in a firm steady pull to the full value.

When you are all done, and before reinstalling the spark plugs, crank the motor. It is not uncommon to find the coolant has seeped into the combustion chambers while the bolts were loosened. This will prevent nasty surprises, and is quicker than draining the coolant as recommended by the factory manuals. If I do notice a large amount of coolant spewing back out the spark plug hole, time to change the engine oil and most likely that head gasket it already bad.

Replacing the Head Gasket

Give yourself some room, and remove the battery. Two small bolts (6mm, 10mm wrench) are at the front of cylinder head. Remove them. Usually they are hiding under a layer of crud. Remove the top radiator hose. If it is stuck real tight to the radiator neck, it is quickest to slit it off. Always a good idea to replace all those hoses when doing major work. There is also a metal pipe that comes around the front of the engine. Remove the "L" shaped hose by the lower radiator hose fitting on the engine. Get a replacement from Nissan, as the inlet and outlet are different sizes.

Remove the fuel lines, and fuel pump. This is when I hate finding a 8mm x 1.25mm threaded nut that is 13mm across the flats. Buy the 12mm across the flat variety from your local Nissan dealer. Makes life easier. Remove the carburetor linkage. I usually unsnap the rod from the accelerator rod. Leave the rod attached to the firewall and just let it slip out, when you remove the intake manifold and carb. Keeps things simple. Remove the choke cable, if fitted, and any electrical connections to the carb.

Remove the intake and exhaust manifolds.. Once again having the OEM 12 mm wrench sized nuts makes things go much quicker. Usually the manifolds are pretty well stuck in place. Wiggling them with your hand will usually break them loose. If not, I like using a rubber mallet to "wack" them with. You'll damage things if you use a metal hammer!!! Rubber mallet is fine for this. Almost there! Time to remove the six valve cover bolts. Once again a bump of the rubber mallet will loosen the valve cover gasket. Now to remove that cam sprocket bolt. Two possible ways of holding the camshaft:
1. Easiest if it has "lobes" on the middle of the cam. L20B cams usually have them. A nice long adjustable Crescent wrench can grab the lobes, and hold the cam from turning. Use a piece of wood against the top of the head, and rotate the Crescent wrench down against it. Then use a good 1/2" breaker bar and 17mm socket to break loose the cam sprocket bolt. Takes a little effort to loosen, watch your knuckles. You'll soon discover why I recommended removing the battery first. (Use extreme caution if the battery is in place, that the breaker bar does not land against the positive terminal).
2. No lobes on the center of the cam. Makes life a little harder, but to hold the cam in place, you need to run a bar through the cam sprocket against the head. Once again, a couple of hunks of wood will help protect the head, especially the front cover.

It is not uncommon to destroy the locating pin between the cam and sprocket if that bolt had not been removed in the last 25 years.

Once you have just loosened the bolt: Do not remove it yet! I will rotate the engine, by hand, (you were wondering why I recommended removing the spark plugs - makes it easier now). Rotate it so cylinder #1 is at TDC, and both lobes (#1 Exhaust and #1 Intake) are pointing up.

Slip in a chain holder. I have a nifty little plastic item meant for the job, which is great. Nice little pull rope is attached to it to help in removing it. Or you can make your own holder out of a piece of wood. (Figure 1) Straight side is to the right, when you are standing in front of the engine. Push the chain holder into place with a gentle force.

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