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Jaguar V12 Auxiliary Air Valve Disassembly

Jaguar V12

Auxiliary Air Valve

Disassembly and Reassembly

The AAV was never intended to come apart.  The major subcomponents, a baseplate and a cylinder/outlet port (which I will simply call the "cylinder") are both pressed into the housing -- from opposite ends.  As a result, it's not obvious how to press the parts back out; you can't get behind either one.  I will present several ways to proceed here; please read them all before deciding on the course of action that suits you.  First, a picture of the exploded AAV so you have some idea what you're doing:

From left to right, these parts are the cylinder (with the outlet hose fitting at the top, or left end in this pic), the housing (with the warm idle adjuster screw still in place and the inlet hose fitting facing the camera), the spring, the piston, and the baseplate assembly.  The outer edge of the baseplate assembly is a press fit into the bottom of the housing.  The large diameter area on the upper end of the cylinder (left end in this pic) is a press fit into the upper end of the housing; the other large diameter area at the lower end of the cylinder is just a bit smaller, making it a slip fit rather than a press fit.

If you look down through the outlet, you can see the bottom of the piston with the central hole surrounded by a circle of six holes.  If you insert a drift about a half inch in diameter into the outlet so it sits on this piston and then beat it with a hammer or push it with a press, you can push the baseplate out the bottom.  However, it's not likely the thermal bulb will survive.  You are effectively beating on the plunger itself, since that's what the piston sits on.  Of course, if you intend to replace the bulb anyway, this method might suit your purposes just fine.

Jan Wikström suggests making up a tool with six prongs that insert through those six holes in a circle.  Another idea is to simply insert six pins, all about 1/8" in diameter, about an inch long, and all exactly the same length, into the holes and then using your drift and hammer or press.  Either way, you will avoid pushing on the plunger and will push on the washer retaining the bulb instead.  Unfortunately, this washer is thin and you're likely to dent it, but that might not hurt anything.  Again, if you're planning to tear the bulb out of the baseplate anyway and use a different bulb retention scheme (see the pages on installing the Robertshaw or CarQuest thermostat bulbs), damage to that washer may not bother you.  The bulb will most certainly not be damaged by this method, if it's not already bad.

Once the baseplate is out -- by whatever means -- it is a simple matter to push the cylinder out the other way.  Be sure to use a drift that won't damage the inner surface of the cylinder.  Or, consider another option: don't remove the cylinder at all.  There's very little reason to remove it; you can clean and polish the inside of it where it sits.

Greg Meboe came up with a different disassembly method, working in the opposite order: pulling the cylinder out first to gain access to push the baseplate out from above.  What Meboe did was to drill a hole crossways through the hose fitting itself on the outlet end of the cylinder, which allowed him to slide a rod through it and pull on it.  One method that would work would be to obtain a short length of iron pipe with an ID that will fit around the cylinder but rest on the edge of the housing, along with a cap and a threaded eyelet or hook.  The eyelet or hook need to be small enough to fit into the outlet opening and have the rod inserted crossways through it.  Drill a hole in the center of the pipe cap and feed the threaded end of the eyelet (perhaps extended with threaded rod and a coupling nut) through the hole and spin a nut down on it.  Tightening the nut will pull the cylinder right up out of the housing.

Note that the inner diameter of the housing is constant from end to end -- which brings up another method for disassembly, and perhaps the most advisable: press the cylinder down into the housing, and continue pushing until it pushes the baseplate out the bottom.  Simple and straightforward.  Once the baseplate is out you could continue to push the cylinder on through, but it's probably easier to turn around and push it out the top.  The only problem with this method arises if the piston is jammed in the cylinder.  If the piston is free to move, it will simply slide up the cylinder as the cylinder comes down, and the edge of the cylinder will contact the edge of the baseplate before anything else makes contact.  However, if the piston is jammed and won't break loose under this much stress, then once again you will be applying great pressure to the top of the plunger in the thermal bulb.

There is still another method of disassembly to mention.  If you have access to a lathe or mill, you can cut metal off the flat bottom surface of the AAV until the baseplate falls out.  When reassembling, you can fab up an aluminum sandwich plate the same thickness as the amount of metal removed to hold it back together.  If you're going this route, you might chuck the OEM baseplate altogether and figure a way to mount the thermal bulb in the sandwich plate you're making.  This would make the AAV an absolute cinch to rebuild next time.

Once the AAV is apart, the next thing you're probably going to want to do is take the baseplate assembly apart to get the thermal bulb out.  The bulb is held in with a steel washer that is fit into a recess and the edge peened over.

The simplest way to get this thing apart is to select a big socket that the entire baseplate will not quite fit into, so it contacts only around the very edge.  Position the baseplate on the socket with the plunger pointing into the socket, and clamp it all into a vice with one jaw on the end of the socket and the other jaw contacting the blunt end of that copper thermal bulb.  Tighten the vice, and it will push the washer out of the baseplate just as neat as you please without damage to the bulb.  Unfortunately, it will dish the steel washer -- but you can pound it back flat if you intend to reuse it.  Better yet, don't pound it flat until you are reassembling; you can push it back flat while clamping the assembly together and peening that edge back down.

Note that the flange on the bulb is beveled both top and bottom.  The bevel on the bottom fits into a matching bevel in the opening in the baseplate.

The second item from left in this picture is a seal that fits just under the steel washer, on the upper beveled edge of the flange on the bulb and against the ID of the recess in the baseplate.  This seal therefore has a triangular cross section.  Note that this assembly needs to be watertight, as a leak here will allow coolant into the intake.  When disassembled, this seal is likely to be crispy, but it can be effectively replaced with a common O-ring.

The brass collar on the plunger is what pushes against the bottom of the piston to push it up and down.

The black pillbox on top of the bulb where the plunger enters appears to be a rubber seal; its apparent purpose is to keep some grease in the sleeve that the plunger slides into.  It should feel nice and pliable, just like a new O-ring -- but it's probably hard as cee-mint.  This seal is glued onto the top surface of the bulb, but the glue doesn't seem to be a problem; it's the rubber itself getting hard that's the problem.

If you've come this far, you probably want to replace that bulb.  See some guidelines on choosing a donor thermostat, plus two baseplate rebuilding methods documented so far, one using a Robertshaw thermostat and one using a CarQuest thermostat, plus some other ideas.

Once you have the baseplate rebuilt and have cleaned up the piston and cylinder so the piston can slide freely up and down, it's time to reassemble the AAV.  Reassembly is pretty well self-explanatory by the time you get to this point, but I will mention a couple of things.  The joint where the baseplate is pressed into the bottom of the housing needs to be watertight, because this surface is pressed against a gasket that seals the cooling system.  The gasket is actually compressed between the baseplate itself and the left rear coolant manifold (inward of the baseplate/housing joint) and therefore the joint itself should never see coolant, but this gasket compression relies on the press fit being solid and correctly positioned.  Just to play it safe, apply some Loctite 573/574/518 around the mating surfaces of the baseplate and housing before pressing them together.  The outer portion of the gasket compressed by the housing itself against the left rear coolant manifold is reliable, as the bolts are pulling the housing directly, no press fit involved.

The seal of the press fit of the cylinder into the housing is not critical; if there is any leakage, it only raises the idle a hair -- and leaks are not likely to be large enough to admit any damaging particles into the engine.

Dimensions:  how far do you press the cylinder into the housing?  Based on Craig Sawyer's analysis of a brand new AAV and inspection of some others while apart, the distance from the upper edge of the outlet fitting to the inside bottom of the piston at room temperature should be 70mm.  This dimension can be checked without even removing the AAV from the car; just take the hose off the top.  On some AAV's, at room temperature the port is actually not fully open; the wide horizontal slot portion of the 73352 port should be completely covered at room temperature!  The piston will move even farther downward as the temperature approaches freezing, so the distance down to the inner bottom of the piston can increase to 73mm or more.

The thickness of the bottom of the piston is 6mm.  The distance from the bottom of the baseplate to the pushing surface on the plunger at room temperature is about 22mm.  Adding 70+6+22 = 98mm from the mounting surface of the AAV to the top of the outlet fitting.  However, if you have rebuilt your baseplate and the pushing surface on the plunger is a little more or less than 22mm above the bottom of the baseplate, you can easily compensate by pressing the cylinder into the housing a little more or less until you obtain that desired 70mm dimension at room temp.  The overall length of 98mm is not critical, since the hose connecting to it can easily compensate for a few mm one way or the other.

Note that the performance of the AAV -- the temperatures at which it starts closing or fully closes -- can be adjusted a bit by how far the cylinder is pressed into the housing.  The farther it is pressed in, the more the piston is moved up the cylinder at any given temp, so the lower the idle will be.  Since it is difficult to back the cylinder out, it may make sense to press it in only the minimum amount, operate the engine and note the performance, and then press it progressively farther in until the desired cold idle characteristics are achieved.


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