Inlet manifold gasket failure is a common failure on the k series fitted with the 'black plastic' inlet manifold - and can be a big cause of HGF. So heres a brief guide on changing the gasket:
First obviously you need to determine that your inlet manifold gasket is leaking - in the case of this 1998 Rover 416 there was slow, intermittent coolant loss which could be seen when the car had been sat for a good few hours (over night) coupled with misfiring upon startup in the morning (although it only misfired when it leaked) I couldnt decided weather its the head gasket or not so thought I would try changing the inlet manifold gasket first for what its worth.
STEP 1: Unclip air filter housing and unclip the connected hose at the throttle body using a flat bladed screw driver. The whole top half of the air filter housing/box can now be lifted away and placed to one side.
STEP 2: In order to free the manifold and let it lean back you will need to disconnect various pipes and connectors. I started off by just removing the obvious - the 2 oil/breather pipes connected to the rocker cover....(a pair of pliers is needed) and the electrical connection that is secured to the manifold.....more of less directly behind the oil filler cap.
Should be looking something like this:
STEP 3: drain the coolant. Some say dont drain the coolant but I chose to and took the opportunity to flush the radiator etc. To drain coolant remove the bottom radiator hose......on mine I had to remove the lower underside plastic panel as that was the only way I could undo the circlip as it was facing to the ground. To remove this panel is quite obvious - remove the (4 at a guess?) bolts on the underside, and then undo the 2 plastic screws in each front wheel arch.
STEP 4: With the coolant drained, lower the car back down. (I kept it slightly raised some of the times to make it easier)
STEP 5: Is really just having a look to see what may obstruct taking the manifold off. (Or leaning it out of the way) I removed and disconnected things as I went along as I hadn't done the task before, but you can do it before:
-Disconnect the smaller
coolant hose from the 'elbow' at the front corner of the engine - the hose that runs under the distributor and along side the air filter box. Moving this hose helps access to the very end lower bolt on the manifold (same side).
-On 400 models completely remove the small thin piping that runs from the top of the coolant expansion tank, to the manifold, and then finishing off at the radiator....its obvious how to remove it and it just gets in the way other wise.
-If you follow the the fuel piping from the fuel filter, under the manifold you will get to a metal clip that screws to the manifold....unbolt this - it doesnt free much space as the pipes are metal so 'non bendable' - but every little helps.
-Remove the centre HT lead from the distibutor cap and free it from the manifold as its clipped to the underside and gets in the way. (No need to remove it from coil)
-follow the throttle cable from the throttle body, and free it from any clips
- some of the electrical connectors/sensors around the throttle body area etc. get in the way so just un-clip them
STEP 6 - once you have had a look and disconnected everything that will get in the way, you are now ready to remove the bolts of the manifold.
You need a size 10 socket for the lower bolts, and a size 13 socket for the 3 upper nuts. Access can be very fiddly indeed - just take your time ,and try using various extension bars. (you would be surprised how just using a differnt socket/extension bar can make all the differnece) There should be 4 lower bolts, and 3 upper nuts.
Once the nuts/bolts have been removed and put aside, gently wiggle the manifold with both hands to free it if its stuck. It will start to come away and then you should be able to pull it away from the engine and ease it off the top studs.
There should now be a small gap between the manifold and the engine, I think I had already removed the old gasket in this picture:
With a bit of persausion you should be able to move the manifold enough (again check any cables etc. getting in the way) to remove the old gasket....It will probably be a bit 'stuck' in the grooves of the manifold.
Cleaning up, and reassembly..................