Find TDC
- Thread starter 69 Mach 393
- Start date
krash kendall
Active Member
Take off the passenger side valve cover, turn crank to 0*. If both valves on cyl #1 are closed you are at TDC, if not then turn the crank one more revolution. Make sure your lifters are pumped up.
SoCalCruising
Founding Member
It doesn't matter so long as your balancer is clocked for the timing mark you are using. If you are using a stock-style balancer, clocked for the 2:00 timing marker, you will have to re-tape the balancer. To do that, you have to find exact TDC, then place the tape's "0" at your new timing marker. I don't know how to find exact TDC without removing the heads. If you bought the balancer clocked for your new pointer, you're good to go.
After you find TDC, you might want to add this timing tape to your balancer:
Part no. MSD-8985, $3.95 at Summit (plus $7.50 s + h).
An easier way to find TDC than to remove the valve cover (and you know there are TWO TDC's, right?) is to crank the engine with your thumb over the plug hole for #1. You can do this with the ignition off and the coil wire disconnected, by jumping a screwdriver or even a house key across the solenoid, from the post where the battery attaches to the next post over.
When your thumb gets blown off by compression, that's TDC Compression. Now stick a screwdriver in the hole and with a socket wrench rock the balancer back and forth and watch the screwdriver handle. It will move up and down. When it's at the lowest point, the piston is at its highest. That's exactly TDC.
Now you tape on the right-sized timing tape on your balancer, with the "0" at the pointer.
Part no. MSD-8985, $3.95 at Summit (plus $7.50 s + h).
An easier way to find TDC than to remove the valve cover (and you know there are TWO TDC's, right?) is to crank the engine with your thumb over the plug hole for #1. You can do this with the ignition off and the coil wire disconnected, by jumping a screwdriver or even a house key across the solenoid, from the post where the battery attaches to the next post over.
When your thumb gets blown off by compression, that's TDC Compression. Now stick a screwdriver in the hole and with a socket wrench rock the balancer back and forth and watch the screwdriver handle. It will move up and down. When it's at the lowest point, the piston is at its highest. That's exactly TDC.
Now you tape on the right-sized timing tape on your balancer, with the "0" at the pointer.
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wild70stang
New Member
- Nov 11, 2005
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what ever happened to the old fasioned way of having one person turn the key and the other person sticks their finger in the spark plug slot?
jerry S
New Member
You can also thread a piston stop in the #1 spark plug hole and turn the crank until you encounter the stop. Voila! TDC
SoCalCruising
Founding Member
Can you have both pointers on the block simultaneously? If so, use the old pointer and current balancer to find TDC (using finger over spark plug hole, or watching rockers), then retape the balancer placing "0" (on the new tape) at the new pointer.
I was about to jump on this and say you could be 180* off but you covered it very well, is that where your handle comes from?180 Out said:
I recommend a popsicle stick or even a pencil be inserted into the chamber rather than a metal object though. I've used my pinkie finger before too, I can get even more precise feeling the piston move, just make sure you are hand cranking the thing not using the starter!
krash kendall
Active Member
180 Out said:
No! TDC is at the TOP of the compression stroke. If you turn the crank back and forth untill the screwdriver drops to its lowest point then you are either at the bottom of the intake stroke or bottom of the power stroke. There is only one TDC per cylinder.
krash kendall
Active Member
69 Mach 393 said:
This will happen during the compression stroke through to the end of the power stroke then the exhaust valve will open. This is the only time during the cycle that both valves will be closed.
krash kendall
Active Member
Yes, but he said when the screwdriver is at its lowest the piston will be at its highest. Do they exchange or share the same piece of space-time with each other? Somebody has given him some wrong information or he misinterpreted some advice.
SoCalCruising
Founding Member
I was with you KK, but then I thought the screwdriver is pivoting, not moving up and down in sincrony with the piston. When it pivots (pivot point at the spark plug whole), the handle will move down when the piston moves up. It isn't intuitive until you picture the setup in your mind and realize that the screwdriver is pivoting.
krash kendall
Active Member
Gotcha! Whenever I've done that I've always pulled the screwdriver out as the piston comes in contact with it to avoid damage. There is still only pne TDC per cylinder though - Top of compression stroke, both valves closed.
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