How2 - Change the C25XE Cam Cover gaskets

[humbucker]

A common failing on the V6 engine are the cam cover gaskets. This is a result of poor design of the crankcase breather system and owner neglect; both in equal measure.

If the breather system gets blocked then excess pressure can build up within the cam covers, causing the pressure to push out a gasket. Subsequently, oil can fill the spark plug cavities and/or leak outside of the cam cover down the back/side of the head.

When working on the procedure below it is vital that you clean the crankcase breather system at the same time. This will be documented on another How2 thread on this website so take a look at it.

Ideally you should only use the parts listed below. Non genuine items are usually a bad fit and you will find yourself having to replace them again in a very short space of time. The genuine gaskets can be repositioned for up to six months if you have problems:

90511451 Cam cover gaskets (one set per bank)
90411826 Cam cover o-rings (eight per bank)
90485251 Sealant (black stuff only, do not use grey or green sealant)
90412126 Upper inlet manifold gasket (optional; depends on condition of your existing item)
09195109 Spark plug (six required)
A plentiful supply of tea

You will need a good tool kit including a selection of torx sockets and a torque wrench. Undertake the following work when the engine is cold.

First, disconnect the battery negative terminal. Next, remove the torx bolts that hold on the engine cover (if original engine cover is still present):

Unclip the throttle cable by removing the wire pin holding the ball to the lever. Next, using a ratchet spanner, remove the two torx bolts holding the throttle assembly to the upper inlet manifold. Then undo the remaining torx bolts holding the wiring harness to the upper inlet manifold. Undo the jubilee clip that holds the throttle body to the airflow pipe and remove the breather pipe from the side of the throttle body using the same method. Unplug the sensor on the side of the traction control/throttle body (if present):

Carefully undo each of the bolts that hold the upper inlet manifold in place. Some of these are longer than others so it should be obvious which ones go where when you need to put them back. You may need to unclip some of the sensor wires that are in place depending on how generous GM were at the factory with their length of wire the day your car left the production line!

Carefully lift the upper inlet manifold out of the way and place a piece of tissue in each of the cavities leading into the head; the last thing you want to do is drop something down there. You will be able to ascertain at this stage whether or not your upper inlet manifold gasket needs replacing (green item pictured below):

With the inlet off you can now pull the HT leads out and see if your leak is contaminating the spark plug wells. Using the spark plug pulling tool provided with your engine pull each of them out. Remember the order they were in if they are not labelled (tip: the order your HT leads need to return to is printed on the cam cover nearest the front of the car).

As you can see from the image below, in addition to a leak running down the back of the head onto the exhaust manifold (producing smoke) the plug wells are filled with oil. If not treated this will destroy the HT leads as well as the spark plugs which now obviously need replacing. Clean up any oil covering the HT lead(s). A cotton bud is a good tool to use if oil has contaminated the inside of the HT lead.

Once you have removed the HT leads, unscrew each of the torx bolts holding the cam covers themselves and pull them free. This may require some effort depending on how much sealant has been used during the last fix, but don’t be too heavy handed.

Using a ratchet and a spark plug removal socket unscrew and remove each of the spark plugs. Any oil filling the well will drop into the engine, but this is nothing to worry about as it will burn away after a couple of minutes of idling (although prepare for the street to be temporarily filled with smoke when you fire the car back up!):

Comparison of new spark plug and contaminated plug with spark plug removal socket:

Return to the cam covers. Clean them thoroughly, removing every last instance of old sealant. Make sure there is NO sealant anywhere on the covers, particularly in the channel that houses the gaskets, and remove any bits of old gasket, including the old o-rings. Spend time doing a good job here as it will save you having to do the job again if the seal is compromised due to old sealant/gasket preventing a proper seal. Ideally no oil, sealant or gasket should be left after you have cleaned.

(Tip: check that the face of the cam cover is flat as there are a lot of reports of ‘warped’ cam covers due to overtightening of the torx bolts. I have yet to come across a warped cam cover, they are pretty sturdy items, but if you have any doubts then renewal of the covers is a good idea.)

Fit your new o-rings and cam cover gaskets ensuring a snug fit.

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Use some strong paper towel and a flat head screwdriver to absorb any oil left in the ridges within the plug well, but be super-careful not to drop any tissue down the hole. Fit your new spark plugs once you are satisfied that you have removed the majority of the oil from the plug wells:

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Once you have cleaned the cam covers (and fit your new gaskets and spark plugs) you must remove any sealant and grime from the cam cover mating surface. This must be as clean as possible and you will need to pay particular attention to the corners and ‘half moon’ areas.

(Tip: If old sealant is proving stubborn then some white spirit, elbow grease and a flat head screwdriver will be of use!)

Once the mating surface is completely free of old sealant you can apply your new sealant. This stuff dries quckly so apply to one cam cover at a time. IMPORTANT: you do not want to apply sealant anywhere other than the corners (either side of the cam clamps) on the drivers side, and the half moon cut-outs on the passengers side. Don't be too generous with the application of sealant, and certainly don’t be tempted to apply it all the way along the gasket/cam cover.

Gently place your cam cover, complete with renewed gasket, back on to the mating surface and press gently into place. Take a quick look and feel to check that the cam cover gasket has not moved (or you will be looking at a very big oil leak, particularly around the half moon area!). Check to make sure that the knock or cam sensor wiring has not been trapped under the cam cover. If satisfied, screw the cam cover torx bolts back in, not exceeding 8Nm. Anything tighter than this will result in a leak within a few weeks.

Apply the sealant and repeat the process for the remaining cam cover.

Then, as Mr Haynes likes to say, reassembly is the reverse of removal. If your plug wells were filled with oil you can expect the neighbours to enjoy a big cloud of smoke as you fire up the engine. Nothing to worry about, it will clear.

As mentioned before, it is vital that you clean the crank case breather system on your car when you undertake a cam cover gasket change as it is likely to be a blocked breather that caused the leak in the first place. See this How2 guide for instructions:

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