TDC

[PromiseKeeper]

Can some of you tell me the easiest way to find Top Dead Center on a 305? I want to run a leak down test and see whats going on with the engine. After finding TDC, I just need to follow the firing order and move the engine one full rotation for each cylinder, correct?

[Captkaos]

A cyclinder leakdown test.  You don't need to know TDC.  Just get a pressure gauge screw in the gauge and crank it over 4 times take the reading and move to the next one.

[HAULIN IT]

Chris, He's talking a leakdown...not a compression test.
Promise, Is this engine completely assembled (timing cover, balancer, ect.)? If not, more effort will be needed. If so, pull the #1 plug, ball up a piece of paper towel, sheet of paper or similar & lightly push it starting into the spark plug hole, rotate the engine over clockwise until you hear a "pop"...the paper being pushed out by the compression, rotate on around until the line on the balancer lines up on "0". Do your test. Go through the firing order doing each cylinder. Install the plugs back in each cylinder when done with that hole...this keeps the engine from rotating from the forced air. It is best to loosen the rocker arms when doing the test. Lorne

[PromiseKeeper]

Lorne,
That sounds like a plan. Thanks for the shortcut! Yes, everything is completely assembled. Why is it best to loosen the rocker arms? They would keep the valves from leaking?

[79gmc15]

Here is a cool way!
 https://www.youtube.com/watch?v=u2sA-q7_FtQ&feature=youtube_gdata_player

[bake74]

Here is a cool way!
 https://www.youtube.com/watch?v=u2sA-q7_FtQ&feature=youtube_gdata_player

     I have done this before, I still prefer the screwdriver method.

[Captkaos]

Sorry, my bad....  in that case do it as Lorne indicated.

Chris, He's talking a leakdown...not a compression test.

[PromiseKeeper]

bake,
I looked at that website and didnt see a video for the screwdriver method.....would you mind giving me some instructions? Thanks!

[bake74]

     That website only showed the vacuum/psi gauge method. 
     My dad showed me the "screw driver" method.  You take the spark plug out on the #1 cylinder, take a slim screw driver and stick it in the hole to find the top of the piston.  ( what ever you do, keep it straight on top of the piston, I had someone who let it go side ways and ended up screwing up the walls of the cylinder ).
     Then like in the video you turn the crank until the screw driver is at the very most top of the throw and right before it starts to go back down.  While you are doing this you will need the dist. cap off so you can see the rotor.  It should point toward #1 cylinder when it is TDC.  ( depending where your timing is set, it might be a little left or right of pointing directly at the #1 cylinder ).  If it is pointing the opposite direction you need to rotate 180 degrees.
     This is the way I always find TDC on my older vehicles and has never let me down, especially once you get the hang of it.

[PromiseKeeper]

Everyone needs a guy like your Dad in their life, Bake. Common sense is always best. Thanks!