Aprilia firing order

[nistri]

Maybe somebody can help me to understand an apparent anomaly concerning the description of the Aprilia firing order.

1. The factory stated that the firing order is 2-1-3-4. The distributor shaft rotates clockwise when viewing it from above in front of the engine.

2. In the drivers' instructions booklet Fig. 10 shows a scheme of the HT cable connections that will give a firing order like 2-3-4-1.

3. How can this difference be explained?

Any help will be greatly appreciated. Thanks, Andrea

[Sliding Pillar]

It all depends how you number the cylinders!  I have always timed aprilias with the firing order 1 2 3 4 where the cylinders are numbered as follows; standing infront of the engine No1 is front left, No2 is front right, No3 is rear right, No4 is rear left.
I have come across several Aprilias that have not been running correctly because the ignition leads have been fitted in the wrong order and have seen one article where the firing order was incorrect!

[nistri]

Thanks for your comment. I agree with you about the numbering of the cylinders which indeed correspond to the way Lancia numbered them. However, if you fire them in the 1-2-3-4 order, you are not following the Lancia 2-1-3-4 sequence. Or did I misunderstand you? Best regards, Andrea

[nistri]

Sorry, one extra query (apologies for being a pest): if you use the 1-2-3-4 sequence, probably you are causing an imbalance in the engine operation because, on a V4 engine, to keep the running smooth, you should fire one cylinder per side in alternation, right? All the best, Andrea

[johnturner]

The Lambda is similarly timed to fire the cylinders as it were in rotation, first one side then the other. It sounds odd but seems to go OK.

[ben]

        I have allways thought it ridiculusly confusing of Lancia to number the cylinders as "sliding pillar" describes rather than the conventional order of the crank-pins along the crank-shaft.If you take the engine to bits you will find they do of course use this conventional numbering on the components ie pistons con-rods etc.
        I personally find it easier to avoid confusion by treating it as if it was an in-line engine with conventional numbering and a firing order of 1 3 4 2.
        However when setting the timing it must also be remembered that the marks on the flywheel correspond to nos 2@3 pistons (in "straight four" convention) being at top dead centre!!!
        I guess the narrowness of the vee means that alternating the firing from one side to the other isnt an issue.

[nistri]

Ben
Thank you for your reply. The 1-3-4-2 firing order is basically the same as Lancia stated (2-1-3-4) as long as it starts with #2 as you pointed out. However, I still don't understand why the Figure in the Lancia booklet shows a different firing order. Any ideas? Andrea

[JohnMillham]

It all depends how you number the cylinders!  I have always timed aprilias with the firing order 1 2 3 4 where the cylinders are numbered as follows; standing infront of the engine No1 is front left, No2 is front right, No3 is rear right, No4 is rear left.
I have come across several Aprilias that have not been running correctly because the ignition leads have been fitted in the wrong order and have seen one article where the firing order was incorrect!

There is only one firing order which will enable the engine to run on all cylinders. If in any doubt, look at the valve positions by removing the rocker cover. I wonder why Lancia messed around with the cylinder numbering system and changed it for different models. Why should the number one cylinder of a Lambda be the one nearest the driver (on a RHD car)? Any ideas?

[nistri]

"There is only one firing order which will enable the engine to run on all cylinders."

As indicated by Sliding Pillar, these engines can run, although roughly, with a different firing order. This is something I have seen myself.

The numbering of the cylinders remains a mystery to me like the difference between what Lancia stated and what they illustrated in their book.

Best, Andrea

[GG]

Clearly a mystery. My Aprilia instruction and parts book (Dec 1952) has no figures (only tavs) and no indication of a firing order that I could find in it.

Hmmm.

[Charles]

because, on a V4 engine, to keep the running smooth, you should fire one cylinder per side in alternation, right? All the best, Andrea.

I know nothing of the firing order of the Aprillia but I do know that on the Gamma (flat 4) it is 1-3-2-4 in other words it fires both cylinders on one side and then both on the other which is sort of counter-intuitive but doesn't seem to lead to roughness.  This seems to endorse Ben's post above.

[ben]

   There really is no mystery about the firing order on the Aprilia. The order is 1-3-4-2 where no1 is the front cylinder (on the right bank of the vee as you look from the front) ,No2 is second from front,(on left hand bank),No 3 third from front,(right bank like No1) and No4 is at the back,(left bank like No2).
   The confusion arises because the numbering shown on the plug connectors in the wiring diagram illustrations relates to the number sequence of the sparks from the distributor rather than the order of the cylinders as described above. I believe the original distributor caps had numbers cast on them (in the simple order of rotation) and hence the plug connectors were numbered to directly correspond to the numbers on the cap--- to avoid any confusion!!!!!
   In practice this leads to the No1 cylinder being labelled No2 and vice-versa for No2 cyl. whereas Nos3@4 correspond correctly.

   If the timing is set on the wrong cylinder but with the connections in the right order the engine will  not run at all. However even if the timing is set correctly it is still easy to get the leads in the wrong order so that only one or two cylinders are working.The engine will run on two cylinders but not very well!
   Even though the engine is a vee the crankshaft is designed to give 180degrees between the pistons reaching top-dead-centre (ie even spacing between firing strokes) so even if the timing is set on the wrong cylinder the engine can be made to run properly by juggling the plug leads.   

[GG]

This issue of firing order vs. distributor cap numbering order is familiar. Aurelias and (I think Flaminias) had numbered caps, and people were always messing this up. That is, the cap # are order in which the spark leaves the cap, whcih then has to be "interpreted" to correct place (or firing order) of the cylinders. Not too complicated if you know this, but a real leap of faith if you don't.

In the past, people have been known to buy badly running Flaminias in the US (due to this issue) go down the road and then change the firing order to the correct sequence. Maybe Lancia had this in mind: if yo don't know this about the cars, you should not be working on them?

Peculiar. Sensible in an old world sort of way, as it allows uncertainty about numbering the order not to interfere with your knowledge of how the cap works. But having cap numbers, firing orders, and then cylinder numbers in the heads (top of combustion chamber hidden away) does allow for some confusion.
 
 

[ben]

Just been looking at some old Magneti-Marelli distributor caps. Contrary to my memory referenced previously I cannot find one with 1-2-3-4 in sequence. The one on my car just has the number 1 (which goes to No2 cylinder of course!). I have two others numbered clockwise 1-3-4-2.They are possibly Appia ones. The cap on my S2 Appia looks interchangeable with the Aprilia.
The Appia numbering is nice and clear however with 1-3-4-2 on the cap and the cylinder numbers, 1-2-3-4 from the front, actually cast into the head and very visible. I guess Lancia had learned some lessons from the Aprilia days.

[nistri]

Many thanks to everyone for the very helpful comments. I think Ben's explanation about the "real" cylinder numbering can account for another unusual feature I could not understand, namely the reason for the 1/3 mark on the bell housing for valve timing. If #1 is actually what is called 2 (or viceversa however one wants to call it), and is at TDC with 3, then it all makes sense (I hope). Best regards, Andrea