What is Top Dead Center TDC of an engine

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This is a very important part of the engine's timing which will allow us to set our distributor in the correct place. It's a good time to show you what TDC is and why we use it.

On the driver's side of the timing cover, there's this little ear with a notch in it. We use a 16 millimeter socket and ratchet on the center bolt of the crank pulley to rotate it. This is a bit more difficult with the engine assembled because you'll have compression you need to deal with. Rotate it clockwise only nice and smooth and slow. You'll see a notch on the crank pulley. This notch right there tells us that our piston is at top dead center.

This means that the number one piston is at its highest point in the cylinder bore, and you can see that this is actually almost flush with the deck of the block at this point. The other important part is that we're going to want that on top dead center compression. Now if the engine was together right in those last few degrees before I got that line marked up with the crank, it would get really tight because of the compression in the motor. If you don't feel that compression when rotating it, it means that cylinder number one is in its intake stroke, which is not what we're after for timing.

However, when there's no compression due to the head being off right now, another easy way to check is both our lifters are down. You can see what one looks like when it's up here. These are what open the valves. These are a part of what open the valves in the vehicle, so if they're both down, both our valves are closed. Our piston would be at the top of the bore and our engine would be in its compression stroke on cylinder number one.

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