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Setting the Engine at Top Dead center
 
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Pelican Technical Article:

Setting the Engine at Top Dead center

Steve Vernon

Time:

30 minutes30 mins

Tab:

$0

Talent:

**

Tools:

19mm off set wrench, 24mm wrench

Applicable Models:

Porsche 993 Carrera (1995-98)
Porsche 993 Carrera 4 (1995-98)
Porsche 993 Carrera 4S (1996-98)
Porsche 993 Carrera S (1998)
Porsche 993 Targa (1996-98)
Porsche 993 Turbo (1996-97)

Hot Tip:

Mark the direction of the belt if you remove it.

Performance Gain:

Allows for other work to be preformed on engine

Complementary Modification:

Replace the belts

If you are going to get into servicing the engine on your 993, you will start to hear the term TDC or Top Dead Center. This term is used when the number one cylinder is at the very top of the compression stroke. This position is used for many things including setting the timing on the cams and distributor and is very handy to know. The engine in the 993 is what is termed a contact motor, which means that the pistons will make contact with the valves if the motor is out of time between the camshafts and crankshaft.

To set the motor at TDC you will need to turn the crankshaft and this can be done with the motor in or out of the car. Many people use the starter motor to "bump" the motor or turn it. While this is fine, if you have any doubts about anything in the motor being amiss, it is better to try and turn it by hand. This will let you know of any trouble using hand pressure verses the starter motor which will do damage before you can stop it.

This article will show you how to set TDC by using both the crankshaft pulley and the alternator belt pulley.

Whether the motor is in our out of the vehicle the engine needs to be turned over by moving the crank which you always want to turn clockwise while facing the rear of the motor (red arrow).
Figure 1

Whether the motor is in our out of the vehicle the engine needs to be turned over by moving the crank which you always want to turn clockwise while facing the rear of the motor (red arrow). This can be done using both the alternator pulley and the crank pulley.

You can only turn the crank pulley and the alternator pulley while the belt is on and properly tensioned.
Figure 2

You can only turn the crank pulley and the alternator pulley while the belt is on and properly tensioned. If the belt is on and under the correct tension use a 24mm wrench place it on the alternator nut (red arrow) and turn the pulley clockwise.

If the belt is off you will need to turn the engine by the crankshaft pulley.
Figure 3

If the belt is off you will need to turn the engine by the crankshaft pulley. You will need a 19mm off set wrench due to the very limited space between the crank pulleys and the engine hanger.

You will need to feed the 19mm offset wrench between the hanger and pulleys and set the wrench on the crankshaft nut (red arrow).
Figure 4

You will need to feed the 19mm offset wrench between the hanger and pulleys and set the wrench on the crankshaft nut (red arrow). You will need to do most of this by feel as there is very little room to see let alone work.

Rotate the engine clockwise until you see the TDC witness mark in the pulley (red arrow) line up with the mark on the fan housing (yellow arrow).
Figure 5

Rotate the engine clockwise until you see the TDC witness mark in the pulley (red arrow) line up with the mark on the fan housing (yellow arrow). There are several witness marks on the crankshaft pulley; TDC was marked with paint from the factory but this could be worn off by now. You will need to check that the engine really is at TDC by removing the distributor caps. Please see our article on replacing your distributor caps for further assistance.

To ensure that the motor is the TDC of the compression stroke you need to see the rotors on the distributors.
Figure 6

To ensure that the motor is the TDC of the compression stroke you need to see the rotors on the distributors. With the caps removed the rotors should line up with the witness marks on the distributor housings (red arrows). If the rotor are off by a very small amount the timing may be off; if they are way off then the motor is not at TDC and not on the compression stroke.

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