Distributor/Advance Story
Updated 04/21/2005
My distributor Alignment was the first
step in my quest to tune to correct my rich mixture.
Advice from David and Tony on the
TTN
Bob, I think that Tony is correct. You are assuming that #1 is at TDC when valve no 8 is fully open, I was with you on this but thinking it through on a piece of paper this isn't right.
Sorry to repeat you Tony but this is how I understand things!!
Pistons #1 and #4 are always at the same height in their respective bores as are pistons 2 and 3 like so.... |-|_|_|-| and at the point where valve 8 is fully open (as in your photos) #4 piston is still going up on its exhaust stroke and piston #1 is still going up on its compression stroke. This is why your mark on the crankshaft pulley is in 'Advance' of the correct position.
As piston #4 travels up, no8 closes (as you say in your pictures) and 7 starts to open. When valve no 7 is equally open with no 8 you are on the overlap period for piston #4 and here is where #1 and #4 achieve TDC - now check your crankshaft pulley it should be near enough at the TDC mark. (why doesn't #4 piston hit the valves at this point? anyone?)
So from your photos when you say 'no 8 coming up a lot' that is because the piston is rising up the bore and hasn't yet achieved TDC.
From your photos, when the timing marks are aligned at TDC your rotor arm has already passed where it should be to line up with #1 terminal in the cap, as Tony says - you should move the distributor drive clockwise one tooth!
On my distributor (Delco) that position is arbitrary because the whole distributor can be rotated to align the rotor with the correct terminal, but yours has a much more bulky vacuum unit which restricts movement. As it happens at approx #1 TDC my rotor aligns pretty much like Bobs 1st picture in the post above - the position that you should achieve if you move your distributor drive gear a tooth clockwise!!
Does all that make sense?
(Apologies again to tony for re-writing his post.)
I repositioned the gear "dog" to align it at
TDC to the firing position of #1 piston as suggested above.
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