Spark fire 2x per TDC or 1??

[kpdiamond]

Another dum-dum ? here....
'02 Ducati M620  2V
Lets say your bike has no cylinder heads on it.  You are going to re-install the heads and time the valvetrain/motor.
We all know that you line up the mark on the crankcase...then the marks on the vert head, then the marks on the horiz. head....

But here is the ?

When the mark on the crankcase is lined up.  That means the horiz. cyl is at TDC.  You can verify this by looking in the sight glass for the flywheel mark.

------BUT------

Even if you have both the crankcase mark, and flywheel mark lined up, and are seeing that the horiz. piston is in fact at TDC.
--It could be TDC exhaust, or TDC ignition---right?  (remember there is no head on the bike to put your finger over the spark hole)

If the above is true:  How might you know if you are TDC ignition, or TCC exhaust?

--Or does it not matter meaning that the coil throws a spark at both TDC positions..Ignition and Exhaust

I have not yet removed the horiz. head, so my reference point is still intact.  But I am going to have both heads off soon.

Go ahead and have a chuckle at my expense...but please offer a useful suggestion in return.

[Speeddog]

When the layshaft pulley mark is lined up with the hashmark on the cases, it's at TDC ignition on the horizontal cylinder.

[kpdiamond]

When the layshaft pulley mark is lined up with the hashmark on the cases, it's at TDC ignition on the horizontal cylinder.

So the only time that the marks on the case and the pulley line up is on the ignition stroke, horizontal?
It wont line up at the same marks on the exhaust stroke?

[Speeddog]

No, the layshaft pulley turns half the speed of the crank.

[kpdiamond]

No, the layshaft pulley turns half the speed of the crank.

Roger that.  Thank you again.  You are a real asset to this community