timing problems

[66Sprint6]

went to check the timing the other day after puttin the new headgasket on, took the #1 plug out to verify TDC visually and noticed that TDC mark on the dial and the mark on the crank pulley dont line up at actuall TDC...whats that all about? If I set the timing at 10* advanced using the actual mark on the crank pulley, the car runs ok but you have to rev the hell outta it to get it to move from a stop and the vacuum at idle is looooow. Could the mark be off or is it because Im usin lower compression forged pistons (flat tops) that this is happening (the not lining up part). I made a new mark on the pulley usin TDC of the piston and it runs pretty good at 10-12* advanced, but pings around 10psi boost...GRRRR.... Whats goin on and what can I do to solve this???
Matt

 

[Mercury Mike]

If you're using shorter pistons, then the real TDC is wherever the pistons at top dead center are, I think. You should use that as TDC. But if it pings there with boost... I don't know what to tell you. Just giving my thoughts. Someone correct me?

 

[addo]

TDC will only change marginally if replacement pistons have a different pin offset. It seems pretty common for the US-made balancers to slip, and that is more possible in Matt's situation.

 

[hasa68mustang]

Im with addo and am going to say the balancer slipped at some point

 

[66Sprint6]

if it slipped, do I make a new mark like I did using the actual TDC while lookin at the pistons?
Matt

 

[addo]

Yep, you do. Probably easiest to make a "dead stop" using a sparkplug and bolt.

 

[Anonymous]

Take and old junk plug and weld a bolt in the center about 1-1/2 inches long. Make the end of it rounded.

Take all the other 5 plugs out so the engine is easy to turn.

Put your plug bolt in #1 hole and thread it in. Turn the crank SLOWLY and GENTLY until number 1 piston hits the stop. Make a mark on the balancer.

Now turn the crank backwards (almolst one full turn) until the piston hits the stop again. make a nother mark.

NOW measure the distance between the two marks you made, and find the half-ways point between them. You now have true TDC.

.......that is, until the balancer decides to slip again....

 

[addo]

You can also mark across from the hub to outer ring when doing this. That "match mark" will tell if the balancer does slip again.