One important thing to remember about finding TDC using the crank pulley, especially with American cars – when the TDC line is marked on a rubber-coupled harmonic “balancer” (in quotes because they don’t balance anything), if the balancer is more than a few years old it has probably broken loose and no longer indicates TDC.
It’s easy to test for this – with the #1 plug removed and a safe object* inserted in the hole, touching the top of the piston, turn the crank so the line on the balancer lines up with the pointer on the timing cover.
- A “safe object” is anything that won’t jam in the cylinder or scratch the piston crown. I usually use a #2 Phillips screwdriver because it’s blunt-ended and big enough not to bind up, and easy to watch and remove when necessary.
Is the piston at TDC? It better be. If the balancer’s line doesn’t line up with the pointer at true TDC, you need to replace the balancer before you go much farther, and absolutely before you can call the job “done.”
Otherwise you’ll waste a whole lot of your time, much more time-value than the cost of a new balancer.
I’ve been the victim of this before, and I’ve seen far too many others fall victim, too.
Re-marking a failed balancer is a waste of your time and your customer’s money, because the outer ring of the balancer will rotate against the inner hub every time the engine starts, stops, or is revved up.
You can usually tell whether the “balancer” has broken loose by checking the timing at idle with a timing light. If you don’t see the line on the balancer, replace it before proceeding.
A broken balancer is usually accompanied by an unnecessarily rough idle, especially if you can decrease the idle (older carbureted cars only, please) below 500 RPM. A decently tuned, mild V-8 should idle down to 350 RPM before stalling from low air flow. Anything that can’t idle below 1000? Suspect the “balancer” – and know that if it’s broken, you won’t be able to tune the car anyway. much less do more involved diagnostics.