TDC and rotor arm position clarification!

Hi All,

Firstly, apologies if I'm posting too much but I'm falling in love with the mechanics of my X1/9!!

Can I get absolute clarification on the rotor arm position when at TDC.
So, I'm aware that a 1500cc carburetor type X1/9 needs to have its crank set at 5 degrees BTDC (Before Top Dead Centre). This basically is the middle mark of the three marks.
Now, most, if not all of the technical data on this says that when at your designated TDC for your engine type, the rotor arm should be pointing at the cylinder 1 contact inside the distributor cap.
When I checked out a useful Youtube video when changing my cam belt, he mentioned this and said that the literature is wrong and that it should point to the cylinder 4 contact.
When I changed my cambelt, I set my rotor arm to point to cylinder 4 and it seemed to run brilliantly. Am I still wrong though?
Does anyone have any views on this or done a similar thing they could share?
Many thanks,
Gareth.

In the spirit of closing out threads unless anyone wishes to contribute, I came across the below from another forum which seems to explain fully my dilemma.
I hope it helps.


Pistons 1 and 4 move together and opposite to 2 and 3, so any time that 1 is at TDC, so is 4 (and then 2 and 3 will be at BDC).

The crankshaft turns twice for every single revolution of the distributor rotor and the camshaft (because the cam and aux sprockets are twice the size of the belt sprocket on the crank).

So when you are setting things up statically, as when replacing the timing belt, you line up the timing marks on the camshaft and the crankshaft. You will have 1 and 4 at TDC; both valves in 4 will be closed corresponding to the top of the compression stroke ready to fire; and in cylinder 1 the intake will have just opened and the exhaust valve will be about to close, corresponding to the overlap period at the top of the exhaust stroke. Obviously you want the distributor positioned to fire number 4 cylinder.

Now, suppose you were to rotate the crankshaft one full turn. Pistons 1 and 4 will go down and then come back up to TDC and the crank timing mark will be aligned again. However, the cam and distributor will only do a half-turn, so now the timing mark on the cam sprocket will be 180 degrees out, number 1 cylinder will have its valves closed ready to fire, and number 4 will have its valves open for the top of the exhaust stroke. Because the distributor also made a half-turn, it's also positioned to fire number 1.

Give the crankshaft a second full turn, and the cam timing mark will come around and line up again, and we'll be back to firing number 4 again.

Think about this for a moment, and you'll see that once the engine is running and you're using a timing light to get the ignition timing spot on, you can use either number 1 or number 4 cylinder to trigger the timing light. Either way, you will get a flash on every other rotation of the crankshaft, as number 1 and number 4 both move through TDC, with one of them firing.

Your right, it can all get confusing when timing up an engine then when stripping engine confusion sets in as the head castings state opposite cylinder marking to actual ignition firing..... Aww nuts.. what is it supposed to be?

A note to... err note, engine manufacturerersers of our engine era donoted #1 cylinder as closest cylinder to timing marks.. and our lovely engine has timing marks both at pulley and flywheel end!

So for one moment, lets forget what a haynes manual, fiat manual, forum chat state.. just for one moment.. check for yourself using the eyeball, so remove cam cover, and spin crank to align crank and cam marks.. you will then see that crank at TDC and Cam on its marks, that #4 cylinder (flywheel end) is actually the the firing cylinder with both intake/exhaust cam lobes facing skyward... therefore cylinder ready to fire, Number 1... WTF..

Therfore go with this engine curiosity, for ignition timing setup, use the cylinder that is actually firing via eyeball confirmation. soooo normally an end cylinder at flywheel end is #4 is on transistion from exhaust stroke to Induction stroke (overlap) but for this engine it is actually #1 firing.. and timing your engine from that, 1-3-4-2 starting at flywheel end.

Your distributor just wants to confuse you... thats its purpose in life, to confuse and be high maintenance with points. So regardless were you put the belt drive wheel, it just has to be in-sync with your HT lead firing order, but it does help to align it as close any OEM marks, (mine no longer exist, so I just aligned it to fire on my cap that allowed best HT lead run.. if you know what I mean) The rotor arm must point to the firing cylinder on the cap, fine tuning to 5 deg BTDC can be done by test bulb/multimeter/timing light (that is an excerise in another topic for sure, and it is easy to do!!), the rest of the HT leads can be positioned on the cap according to firing order and noting the clockwise rotation of rotor arm. you can put HT leads anywhere you want, just ensure your firing order is correct from flywheel end cylinder.

So my point is this... all ignition timing and camshaft positioning is be been done to the actual engine FIAT timing marks that put flywheel end cylinder as #1, forget what others do! hence TDC on flywheel end (difficult to see yes, but accurate, the pulley end marks can be out by a few degrees because the pointer is adjustable, its on a couple of bolts that allow movement. Camshaft pulley on its marks, to confirm, remove by eyeball. Match distrubritor cap to firing cylinder, then match the HT leads to clockwise rotor rotation of firing order.

I still use points and condensor.. its the one old tech that love and dont want to lose.. Points based ignition (kettering) is reliable and robust... only if you keep on top service requirements, including distrubitor inner workings (centrifugal weights, springs, oiling etc) . Going electronic isnt fool proof and ceratinly not without some issues, granted it will give a strong spark.. but my issues with electronic for the x1/9 are beyond this discussion, and will accept it does of course make service life easy along with a reliable KiloVolt of spark.

To set static timing accurately does take some understanding of the ignition system, to set dynamically is a whizz with a good timing light, if all else fails, twisting the distributor body blindly will certainly get you close. But thats all for another days discussion, and there are certainly more ways to skin that cat called an X1/9 pain in the ass, start you basta*d, late nite tune up!

ohhh and BTW, 1 & 4 are paired like 2 & 3, but a timing light on the wrong ignition timed cylinder will not be correct, the rotor arm spins at same speed as cam, half speed to the crank, so the plug lead firing on the X1/9 engine is the plug firing... just being all corret here as the x1/9 distributor is not a wasted spark system as used in EFI coil pack configuration.. just saying like..

PS... I wholly duff my cap to you getting oily and greasy understanding and working on your car yourself.. more people need to be like that to keep these cars on the road and enjoy.. much is lost to not having the will to have a go yourself and learning by your own mistakes... Geez, I have made plenty of mistakes in my time spannering.. and that is my vocation, and I still get it wrong at the best of times!!

.....wise words Stu.....thanks for contributing.

Gareth.