finding TDC

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D

decavo

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hillbilly desert rat
Adjust valve clearance
Set no 1 cylinder to TDC/compression
Turn crankshaft to align the timing marks at TDC set the grove on the pully at the 0 mark position timing mark.




above is an exert from the FSM when I align the mark to 0 my pistons are not at TDC I am rebuilding this engine the head and timing cover is on..while adjusting the valves it seems the valves are hitting the pistons we are just using a wrench and when it acted up there was no forcing it... the harmonic balancer if off of a different engine crank shaft....

What the heck do I need to line up for this thing to work..
 
Assuming the timing chain is indexed properly, use a compression gage in the #1 cylinder and bump the starter to get max compression on it to find TDC. It helps if you have the valve cover off (obviously) and the harmonic balancer on to visual the timing mark.
 
I lined stuff up according to the FSM it seems to not be right... I know the timing chain is out of wack but the timing marks on the main pully and the timing thingy are not tdc..

on the cam TDC is when the round divot is on top?

on the crank TDC is when 1 piston is all the way up?
 
raydouble said:
When you roll up to tdc the crank pully should point to the 5 on the timing mark (I think it's five)

You can't roll the engine unless the crank and cam are timed correct.....valves would be contacting pistions.
Click to expand...


ok i believe that at tdc the mark on the crank pulley is not near 5 at all a 1/4 of a turn away... I will check this out tomorrow. I also printed out what 88 posted... I will see what the heck we got wrong...
 
raydouble said:
When you roll up to tdc the crank pully should point to the 5 on the timing mark (I think it's five)
Click to expand...

TDC is 0*... not 5*

Pull the valve cover off, pull the spark plug out of number 1 cylinder. Turn the engine while using a piece of wire to feel down the spark plug hole. Turn until you feel the piston come up to the top of it's stroke. Check the front 2 rocker arms, they should both be loose and rock a little if you are in the right spot.

But!!!!!!!.......

It sounds to me like your harmonic balancer has sheared and the timing mark on it is way off and you installed the timing chain bassed on that mark, which now means your valve timing is way off...
 
You'll have to pull the balancer off and take a look at the backside. If it's sheared then the rubber layer that mounts the pulley to the center will look all boogered up... Should be obvious if that's the problem. Mine sheared while driving, but it was pretty obvious there was a bad problem.... :D
 
You don't even need a balancer on it to find TDC....
 
10-4... My ComCast is blinking in and out....


Remove the #1 spark plug.

Place a small precision screw driver or very small rod like feeler in the #1 cyl. DO NOT DROP ANYTHING IN THE HOLE!

Rotate crank till with the feeler you feel the #1 piston come up and eventually to TDC.

Now see the procedure for adjusting the valves? Look for the match marks on the cam gear and rocker shaft thing, the triangle. You should have some fee play in the 1st two.

IF IT'S (The cam gear) 180 DEGREES OFF, IT'S AT #4 TDC... If it's (The cam gear) exactly at 180 degrees, you should be fine to rotate the engine crank another 360 degrees.


Also, you're dealing with an engine the timing is a mystery on. BE VERY CAREFUL when you are doing this and I'd get the cam at TDC 1st so you don't hit any valves.

IIRC, at ***CAM*** TDC you can't hit any valves no matter how many times you rotate the crank.
 
Last edited:
Doesnt even need to be the wrong balencer... Sometimes where they're pressed on, the glue or press loosens up an the outer pulley will turn.


Did the pulley come with the engine?

Do you have lots other pulleys around your shop?
 
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