How to find TDC, or top dead center
OK, you've taken the motor apart on your classic chevy. Dis-assembling the motor is certainly the easy part while working on a chevy small block. I'll bet you took the motor apart with the thought in the back of your mind, "I'll figure out how to find tdc later when it's time for reinstalling the distributor". Now it's time for re-assembly and you need to install your distributor.
Installing a chevy distributor is another article altogether, so I'll cover that on another page.
I did it Myself!With Tools and Instruction
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What is TDC?
Top dead center is when the number one piston is at the top of it's compression stroke.
You will need to find TDC, or top dead center, in order to re-install the distributor in your classic chevy small block engine so that the distributor striker is in the number one position at the same time the number one piston is at the top of it's compression stroke. If your intent is to install the distributor, you won't be able to use the distributor as a reference point, instead you need to refer to the harmonic balancer and find the timing mark.
When you find TDC, this will ensure you start off with your ignition timing as close to zero degrees as possible when it comes time to start the engine. If your ignition timing is not close enough, the motor may not start at all.
Do I need fancy tools?
No. I will show you how to do this with a minimum of tools. Unlike some other articles on the internet that require degree wheels, dial indicators (depth micrometers), or manometers, you can get by on old school know - how for this one.
How accurate is this method?
Your need for absolute accuracy depends on what you are trying to achieve. If you are building a racing engine, you should use precision tools that allow you to account for inaccuracies in the machined parts. If you simply want to install a distributor so that you can get your motor running in your classic car, then this method will do the trick.
This method will allow you to accurately find TDC as long as you do not have any significant damage to the harmonic balancer or the key and keyway, the timing chain, or the timing tab is not bent. On a 64 Impala, and most classic cars in the 60's, the harmonic balancer was made from a single piece of steel so the timing mark will always be in the same place. However, in later years, the harmonic balancer was built with a vibration damper ring and the timing mark was on the damper ring. As the balancer/damper got older and the vibration damping rubber between the balancer and the damper ring started to fail, the timing mark could move. If you have such a harmonic balancer on your motor then this method is "potentially" flawed since you will use the timing mark on the harmonic balancer as your tdc indicator or reference.
Let's get started!
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Find the timing mark on the harmonic balancer. You may need to clean the harmonic balancer to find it.
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Remove the number one spark plug. This is somewhat optional. If you loosen the spark plug so that air can escape from the cylinder, then you can hear the air bleed past the threads when the number one cylinder is coming up to the compression stroke. If you decide to completely remove the spark plug you can put a finger over ( not in ) the spark plug hole. This will enable you to feel the air being forced out of the cylinder as the piston compresses it. Using a finger to cap the hole does not work well when the motor is hot though.
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If you have a remote starter button, connect it to the starter terminals. One clamp goes on the starter solenoid's small wire terminal closest to the motor, the other clamps to the battery cable terminal on the starter solenoid. Use the starter button to crank the engine over in short bursts.
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If you do not have a remote starter button, use a small flat blade screwdriver to short the 2 terminals together. When you have the starter right in front of you, it can be rather loud so you will need to pay attention to the sound of the compressed air escaping from cylinder number one.
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If you use the screw driver method and completely remove the spark plug, you may need someone's assistance to either short out the solenoid or put their finger over the spark plug hole.
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Once you hear the air escaping this means the piston is coming up to tdc. The air does not escapse quickly, it tends to bleed out if the spark plug is still in the hole. Stop turning it over.
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Locate the timing mark on the harmonic balancer. You may need to crank the engine a few times to get it to come around to the timing mark on the timing tab. Don't expect it to stop at tdc, you will be lucky if that happens. You may need to turn the harmonic balancer manually towards or back to tdc.
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Bring the timing mark on the harmonic balancer in line with the 0 degree mark (tdc) on the timing tab. You will notice several lines on the timing tab. The thickest line is 0 degrees and each line represents 2 degrees. Clockwise ( looking at the engine ) of this line is past tdc which would mean your timing is
retarded, and counter clockwise is before tdc which would mean your timing is
advanced. Note how the picture of the timing tab on this 283 chevy small block denotes tdc with a "0" for zero degress advance, and an "A" so you know which side of zero is advance.
Most chevy small blocks will run just fine when initially set to 4-6 degrees advanced. Advanced means the ignition system will send spark to the spark plug before the piston reaches tdc.
