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Motor is @ TDC.. Balancer shows @ 45 degrees BTDC

Vincent Holt

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Location
Wilmington, DE
I have 1967 440 HP motor. It recently has been fully rebuilt. All new internals. I installed the original Harmonic Balancer with no problems. I went to find TDC by using the thumb over the hole whilen cranking technique. When my thumb blew off I looked at the mark on the Balancer and it was way off! Like just over 45 degrees BTDC! I thought he original balancer had skipped or spun out of wack due its age. I replaced it with a Super Damper. SAME THING! It shows 45 degress Adavanced WHAT NOW ? I don't see how the new double roller timing chain skipped a tooth? Amy help would be greatly appreciated!
 
The thumb blew off method is no way to actually check true tdc.
You need a piston stop of some sort.
 
All the thumb tells you is that the piston is coming up on the compression stroke. Not that it is at the top. After it blows your thumb off continue turning the crank clockwise until the TDC mark on the balancer. (Assuming it is correct.)
 
Are you checking the correct piston ?? right front looking at the front.

Also keep in mind that both valves close on the compression stroke well before TDC so you'd have a tough time holding all that compression with your thumb right to TDC !!
 
Maybe a wrong timing cover?
Yeah, maybe they stuck a big block chevy cover on there by mistake !!!

facepalm.gif
 
Best way to determine TDC accurately with the heads on is a piston stop. Pretty easy procedure.
 
Best way to determine TDC accurately with the heads on is a piston stop. Pretty easy procedure.
Agree.

@Vincent Holt
Put a piston stop (see picture below) in the #1 spark plug hole. Turn the engine by hand one direction. When it stops, mark the balancer at the zero indicator on the timing chain cover. Now turn the engine by hand the opposite way until it stops again. Again mark the balancer at the zero indicator. The middle of your two marks is TDC.
By the way, this is easiest if all spark plugs are out so the engine makes no compression as you turn it.

Good Luck!


Piston stop tool:
1713793480807.png
 
Turn the engine by hand one direction. When it stops, mark the balancer at the zero indicator on the timing chain cover. Now turn the engine by hand the opposite way until it stops again. Again mark the balancer at the zero indicator. The middle of your two marks is TDC.
This^^^^^^^^^^^^^^^^^^
............and turn the crank slow but firm. Don't risk damage to the piston.
 
First I've heard of the "thumb method". I must have been checking TDC the hard way for decades.
 
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