Thread: V8 Engine/Distributor Geometry

So, sorry for being dumb because I am sure this is so bleedin' obvious once I work it out - but I am trying to put my dissy back into my V8.

Now, if I turn the engine crank one full turn, the distributor rotor arm turns half a turn.

So at piston 1 TDC there are two positions of the rotor arm - fire on no. 1 and dead opposite fire on no. 1

I assume it matters which way the rotor arm is pointing because the inlet and outlet valves open on opposite strokes (i.e the valves open once for two crank turns like the rotor arm fires once for two crank turns).

So - if I put the crank on the timing mark (at say 6 deg before TDC), how do I know if the rotor arm should be pointing to firing or 180 degrees to firing ?

I can take no.1 plug out but this just shows the piston is at the top when the timing mark is on the dial and this doesn't help with which stroke it is on ?

I really don't want to take the rocker cover off to see what valves are open



So :

a) I am right thinking it does matter which way the dizzy rotor arm is (i.e. fire no. 1 or dead opposite fire no. 1)

b) Is there an easy way of telling which way you need, if you were an idiot and didn't mark anything before you pulled it to pieces ??

A length of heater hose, place one end against no.1 plug hole and blow in the other end. If it's one turn out the inlet or exhaust valve will be open just a little either side of TDC. At firing point the valves won't be open until the piston is way down.