Topic: 1969 351w TDC question

[9F94M567042]

Hey folks, had someone mentioned that if both valves on the number one cylinder are closed that this is an indication that the engine is at TDC. Or close enough to set the timing. Is this anywhere near correct or just BS?

[Bob Gaines]

Hey folks, had someone mentioned that if both valves on the number one cylinder are closed that this is an indication that the engine is at TDC. Or close enough to set the timing. Is this anywhere near correct or just BS?

Both closed ON THE Compression Stroke.  Rather then do that I take out #1 plug put your thumb over the hole and then tap the starter until you feel strong compression blowing out the hole . If you look at the timing pointer it will be close or already on TDC. You have to be careful when tapping the starter (I use 15.00 Harbor Freight remote starter button) because it is easy to blow past TDC . I don't bother taking off the valve cover and looking at the valves because what with the compression stroke confirmed on #1 cylinder and the TDC timing mark on the balance indexed to the timing pointer I have all the confirmation I need. It is easier and typically less messy then taking off valve covers and possibly have to replace gaskets and getting oil all over.  I use this TDC point to drop in distributors or to confirm a distributor has been installed correctly . You can also use it as your base line for timing with a timing light.   

[RoyceP]

Hey folks, had someone mentioned that if both valves on the number one cylinder are closed that this is an indication that the engine is at TDC. Or close enough to set the timing. Is this anywhere near correct or just BS?

It's true but to find TDC exactly you need to be able to see the mark on the balancer which is normally 99.999999 % accurate but it only indicates TDC on every crankshaft revolution so you have to verify both sets of facts - the valves are closed, and the piston is exactly at TDC.


The spark event normally happens a few degrees before TDC. At idle the manual recommends 6 - 12 degrees BTDC for the spark event timing. You can use an ohm meter or a timing light to verify this prior to any gas in the carburetor so that timing is exactly where it should be for first fire up.