*Warning* Do this process at YOUR OWN RISK! If this is done incorrectly you can cause severe engine damage that is expensive and timely to fix.
This process is done on a 1990 Audi 90 Quattro and the process may/will vary depending on your vehicle.
Before we get further into this process, I want to explain some basic knowledge that is needed for this job to be completed successfully.
The timing belt is what ensures correct timing for the valves of your engine. The camshaft dictates when the valves are going to open based off of the position of the crankshaft, this is timing. The timing belt connects the camshaft and crankshaft and MUST be in correct time for your engine to run correctly.
The Risk- As with most automotive jobs, there will always be some level of risk to it. This particular job runs the risk of destroying the valves, pistons, and even the head of your engine. The reason why the risk is so high is because ALL Audi engines from 1977-present are interference engines. What this means is if the valve timing is off even a few degrees, the valves can (and usually do) make contact with the top surface of the pistons. This is a problem because it can/will bend the valves which is an expensive fix.
Finally just use a bit of common sense, do NOT crank the engine without correct valve timing to reduce the risk of engine damage.
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Step 1: Tools Required
1/2 Impact gun
5/8 spark plug socket
6mm allen key
5mm allen key
Phillips head screwdriver
Flat head screwdriver
Step 2: Additional Note...
While you're doing this job, you may as well replace your waterpump. So you'll need a new one as well as some silicone sealant.
Step 3: The Job...
Let's get into it shall we? After each step there is a corrisponding photo...
Step 1: Remove grille and Outside Temperature Sensor. The Temp sensor has three prongs on it, all you have to do is squeeze them and pull it out. The grille should have two screws on the top, and once those are out it should come up and then out.
Step 2: Remove the front support. It will be four 10mm bolts on the outter edges (2 on each side) and three 8mm bolts between them, and two screws at the bottom. Now before you just try to yank that piece out, take a look at the hood release cable that stretches across it, there are three black clips holding it there. To remove from the clips, put your fingers on the cable, push up out of the clip, then push to the front of the car.
Step 3: You don't HAVE to do this step, but it helps to do so. Remove the secondary radiator. It will be the two hoses on the driver's side, and two 10mm bolts on the bottom that you must get from the bottom, and a 10mm swivle socket helps a lot.
Step 4: Next are your accessory belts. The first to come off is the Alternator. Loosen up the 13mm bolt that holds the alternator to the block, then use a 13mm wrench on the gear ratchet on the alternator bracket, turn CLOCKWISE to loosen the belt, and COUNTER-CLOCKWISE to tighten back up. Next is the compressor for the a/c. It has a 13mm bolt and nut on the bottom for the slide, a 15mm bolt on the top and bottom of the side that bolts to the block. Lastly is your power steering pump belt. 15mm bolt on the block ear, 13mm BEHIND the pully, and then to adjust tension, use the 13mm long bolt to move the pump up and down.
Step 5: Remove the 7 shaped braket from the passenger side of the block. It will be two 17mm bolts. HINT; The bottom bolt comes out, the top one does not need to, the bracket is slotted so you can just pull the bracket up.
Step 6: Remove the plastic belt cover from the block. This is helt on using two odd looking nuts. The are flare nuts, but on backwards, to take off, use a 6mm allen socket. You may have to adjust the water pump to remove it, if so, see steps 11 and 12.
Step 7: Now to remove the crank pulley. NOTICE!!! Remove the four 6mm allen blots from the pulley FIRST. If you remove the center bolt and then try to pull the pulley off, you may end up pulling the inner crank drive for the timing belt. So remove the four 6mm allen bolts, then the center bolt, which is 27mm. You may need to put the car into gear to keep the motor from turning (if you have the car in the air), if so, put it in 5th gear to keep the motor from turning over
Step 8. Remove the lower metal cover from in front of the timing belt. This is removed by a 5mm allen bolt on either side.
Step 9: Thread the bolt back into the end of the crankshaft. Put socket back on the bolt. If you put the car into gear to keep the motor from spinning, put in neutral now. Turn the motor over until the Little dot on the camshaft pulley meets up with the arrow on the valve cover. Mark the dot and the arrow with a paint marker or something of the like so that it is easier to see later on. pick a spot on the crank gear and on the block itself and mark with a paint marker to make sure you'll have both the cam and the crank lined up. Pull the spark plug wire on the first cylinder, and then the spark plug with a 5/8" spark plug socket. Stick a long screwdriver or a long 1/4" drive extension down in the hole to make sure that the piston is at top dead center (as far up as it can physically go in the cylinder).
Step 10: Remove the camshaft gear, even with the belt still on. it is easier to loosen and tighten the belt with the water pump once the new water pump is on. I know it's not metric, but i used a 13/16 socket, and it worked fine. If you don't have an impact tool, put the car back in gear for this step and this one only.
Step 11: Remove the Inner metal plate. Sould be three 10mm bolts on the front, a 13mm bolt on the passenger side, and a 13mm bolt for the water pump that must come out. Place the plate off to the side.
Step 12: remove the remaing bolts from the water pump. This will be a 6mm allen bolt on the top of the driver's side, and a 13mm bolt right below it. Also make sure the bracket goes on the same way it came off. The pump should now come right off.
Step 13: Clean the area around where the water pump mounts too with a piece of emry or sand paper. wipe dust off with a shop rag or towel. Put the new seal on the new pump, lube up with some motor oil, but not much, just enough to keep the seal wet. Put the pump on the block, and put the bracket with the 6mm allen bolt and the 13mm bolt back in to hold it on. Bolt that larger metal place back onto the block. now once the passenger side water pump bolt is in, go ahead and loosen the other two back up a bit.
Step 14: Re-install camshaft gear, making sure it is aligned with the marks. Verify that the cranshaft is also aligned with the timing marks. you will notice how the paint marker has now made life a little bit easier . once they are aligned, wrap the belt around the gears and the pulley. Rotate the water pump to set the belt tension. Correct tension is acheived when you can grab the belt with two fingers, and twist the belt just to 90 degrees.
Now all you have to do is reverse the process. Remember to bleed the cooling system after you've re-filled it with coolant.
Special thanks to VWVortex.com for the write up.