944 S2 Head Replacement

It is late in the afternoon, I'm just rounding the corner to pull through the gate at home and my 90 944 S2 Cabriolet starts knocking and sputtering. I immediately recognize the knocking and sputtering as valve related so I gently ease the car to the house and up to the garage door. I suspect a broken valve spring. I've been through broken valve springs before and it was just like this. I'm not looking forward to pulling the car apart to figure out the issue so I leave it in the driveway for a couple weeks.

When I finally do have some time, I start the car, it is still knocking and sputtering but makes it easily into the garage.

I pull the coil wire off of the distributor cap and the ignition wires off of the spark plugs. Three Phillips head screws and the distributor cap is off. M 4 Allen and the rotor cap is off. Not necessary, but I always like to at least start with the engine at top dead center before pulling the timing belt off. There are marks on the gear ring that you can find with some work and a flashlight. I've marked the pulley and housing so I can easily find it from the front. I put the car in third gear and slowly pull or push the car until the mark on the cam pulley is pointing at the white mark on I put the housing. I now remove the fuel lines that run across the top of the valve cover. Be careful not to tweak the hard lines. Use two wrenches, one on the soft line, one on the hard line. Using a thin standard screwdriver I gently slide the wire retainer off of the connector for the ignition timing sensor on the back side of the cam pulley housing and unplug it from the sensor. I remove the throttle and cruise control cables from the intake manifold.10 mm bolts and I pull the aluminum housing for the cam pulley off. A 10 mm socket and wrench and I quickly pull the plastic timing belt cover off of the front of the motor. A 13 mm socket and I loosen the tension slider for the timing belt tensioner pulley. A 17 mm wrench on the tensioner takes the tension off of the belt and I tighten the 13 mm nut to keep the slack on the tensioner. Before I remove the belt I take the bolt for the cam pulley off. Normally this is a Cheesehead. Make sure you use the correct Cheesehead bit or you will strip it out and make it very difficult to get the bolt out. I replaced this bolt with a 7 mm bolt the first time I pulled the cam pulley off on this car. This has made it easier for me. Now I slide the timing belt off of the cam pulley. With the slack on the belt and having removed the pulley bolt, it comes off pretty easily. Don't pry this off if you are going to be keeping the timing belt. For me, the cam pulley slides right off with the belt. After going this far, I prefer to replace the belt with a new one. My preference for timing belts are the Kevlar timing belts. These are stronger and last longer. Even with a Kevlar belt, always make sure you perform your timing belt maintenance on time. The old adage, an ounce of prevention is worth a pound of cure is very accurate when it comes to replacing timing belts.

Now that the pulley is off, there is a disc behind the pulley. This is for the electronic ignition sensor which is in the cam housing. This slides off easily as does the unit behind which is what the rotor attaches to. It might take a little wiggle but whatever you do, do not pry or force it off if it doesn't easily slide off.

Now that I have the timing belt off of the car, I can pull the valve cover off. M 5 Allen wrench fits all of the bolts to remove the valve cover.

Just to try and satisfy my curiosity, I take a quick look to see if I can figure out which valve spring might be broken but all of the lifters are up and solid. To get to the valve springs, I have to remove the cams. I start by removing the tensoiner for the cam chain. This is two Allen screws but before I loosen these, I use an Allen wrench to remove the banjo bolts from the oil line. This is the metal line that connects the tensioner to the head. Once the tensioner is unscrewed, I carefully tilt it out from between the chain and pull it out. I use a Cheesehead bit to pull the front piece that holds down both cams and each of the cam retainers.

I lift both cams out with the chain still attached to both and lay them down on a clean sheet of butchers paper. It is easy enough to set the cam timing but I leave the chain on the cams and don't let it skip so I can easily replace it when the time comes.

I check all of the lifters and still can't tell which valve has the issue so I use a magnet to pull the lifters out. I also place these on a clean piece of butchers paper to resemble the same pattern and order they were in the head. I now have all of the lifters out and the tops of the valves and springs all look right so I start poking at them and realize that the top of the rear exhaust valve for the number 4 cylinder is loose. I grab the magnet and it pulls right out. This means the valve stem is broken, not the valve spring. This means the head has to be pulled.

I start with removing the exhaust headers. A lot of people unbolt these from the exhaust first but I have done this operation enough times on my other 944's to be able to finesse the head out with the headers still there and get them back in with them there. If this is your first time, I recommend taking them out, it will be easier for you getting the head out and especially getting it back in.

Now it is time for me to tackle the intake manifold. I pull the cooling hoses off. These are typically just a hose clamp and a flat screwdriver does the trick on mine. I pull the cover off of the fuel rail. It snaps on and off easily. Using the thin screwdriver, I work the retaining clips off of the fuel injector and sensor connectors and remove the connectors and leave them hanging there. They on;y fit one way so I don't mark them. The Intake manifold is held on with Allen bolts. Make sure you seat the wrench securely into the bolt and don't strip it out. Don't try to pull any of these out at an angle because it will make it more likely to strip and if you strip the head on of these, it is very difficult to get it out. There is a hose connected to it from below. If you do remove this hose, remember that it needs to be reinstalled and tight to avoid any vacuum leaks. Now that the intake manifold has been removed from the head, I'm leaving the intake manifold there.

Now it is time to pull the head off. This is pretty straight forward. Unbolt the head bolts and carefully lift it straight up and out.

I always take my heads to the machine shop. They clean the head, pull the valves and re-seat them with new seals and make sure they aren't warped, cracked, etcetera. The shop I use even cleans and checks out the valves to make sure they are bent at all. They have all of the tools and machines and experience to do this right.

While the head is out at the machine shop, I clean the top of the engine block. Don't use sand paper or anything that can come apart and get into the cylinders, water jacket or engine oil. I use a razor blade scraper to remove any pieces of gasket and clean the top of the block with Acetone.

When the heads come back, I open the new head gasket, place it onto the top of the block and essentially reverse the process. Carefully set the head onto the top of the block and gasket. The less you have to move it around on the gasket, the better. Moving it around a lot and re positioning it increases the likelihood that the head gasket will get damaged.

I thread the head bolts back into head and turn them hand tight. I always use new head bolts because they can stretch. Don't apply any torque to the head bolts right now. Once all of the head bolts are in hand tight, it is time to torque them. There is a pattern to torque the head bolts. I start with the two in the center and work my way out in a pattern. If you don't know the pattern, see the attached image. Torque the bolts to 15 ft lbs. Wait 15 minutes and then turn the bolts another 60 degrees. Wait another 15 minutes and turn them 90 degrees more.

I coat each of the lifters in motor oil and drop them into place over the valve springs. I carefully place the cams onto the tops of the lifters without letting the chain skip. Now I put the tensioner between the chain and turn the two Allen screws in place a few turns to hold it in place and then put the oil line on. Once the oil line is on I torque the tensioner and then torque the oil lines onto the tensioner. Now it's time to bolt on the cams so I line up the lobes for top dead center and double check the location of the pistons through the window in the bell housing. Everything is lined up so I torque the Cheeseheads to 15 ft lbs starting with the center bearings.

Now I put the valve cover gasket on to the valve cover and put it back on, torque it to between 5 and 7 ft lbs. Now I carefully place everything back onto the cam front and bolt the pulley on. I make sure there is no slack in the timing belt and slip it onto the pulley. Now I loosen the 13 mm bolt on the timing belt tensioner to put tension back onto the timing belt then torque the bolt back on.

Now I tackle the intake manifold. I slip the intake manifold gaskets between the head and intake manifold. I take the bolts and slip them through the holes to hold the gasket in place. This takes some wiggling of the intake manifold and I turn them all in a few turns. I don't torque them until all of them have been threaded. Once threaded, I torque each of them down. Again, these are Allens so don't tighten these down at an angle, you don't want to strip the heads of the bolts.

I reconnect all of the connectors for the fuel injectors and sensors. Now to the exhaust headers. I put the exhaust header studs into the head. There are rings for each of the exhaust ports. I put each of these where they go. Sometimes they don't just stay in place so I take a small piece of masking tape and attach it to the head and top of each of the rings to hold them into place. These pieces of tape will burn off when I drive the car. Getting the exhaust header on takes some wrangling to get it onto the head. Finally it is on enough to get the nets onto the ends of the studs and I torque it down.

I replace the timing belt cover, cam pulley housing and reconnect the ignition sensor. Now I carefully put the rotor on. I tap this on before carefully screwing it on. These crack very easily so torque it down evenly and don't let it crack. Now I put the distributor cap back on, attach the coil wire and plug in each of the spark plug wires.

My last step is to reconnect the fuel lines and accelerator and cruise control cables then I reattach the positive battery cable and I am ready to give it a turn.

I put the car in neutral, turn the key in the ignition a few times just to the on position. This gets the fuel pressure back up in the fuel lines. I turn the key to start and she fires right up. Rough for a second or two and then she smooths out. I open the garage door, put the car into reverse and go on a test drive. Everything works.