Why #4 tdc

[dutchdriver]

I have noticed on several topics the person is using #4 tdc for setting the timing gear and belt installation. Why do we use #4 instead of #1. have a 78 124 with 1800 and will be changing exhaust and intake cam seals thanks

[maytag]

If all you're doing is changing belt, etc, then it doesn't matter if you use #1 or #4, as they are both at the top of their stroke at exactly the same time.
When it matters is the ignition timing. When all the timing marks are lined-up, the #4 cylinder is at the top (beginning) of the compression stroke. This is alien to most of us who are accustomed to using #1 for that purpose on other cars.

[majicwrench]

Maytag, ya know I love ya...........it does not matter on ignition timing. Hook your timing light to #1 or #4, it will work just the same.
Keith

[maytag]

Maytag, ya know I love ya...........it does not matter on ignition timing. Hook your timing light to #1 or #4, it will work just the same.
Keith

you're absolutely correct. My point (which I failed to make clearly) was to making sure that the rotor is pointed at #4 when the marks are all lined-up. that's when it matters. but for adjusting timing, you're right, cuz the crank mark will line-up in the correct place whether it's #1 or #4 on the compression stroke.
Thanks for making the clarification!

[dutchdriver]

Thanks for the answer, however it may be because I'm slow but I'm still confused. when replacing timing belt, tower cam seals and gears do I put 1 or 4 at tdc? For lining up the dots in gear with cam mark. if 4 is on exhaust stroke is 1 on intake, this would make timing 180 out?

[majicwrench]

Well, both #1 and #4 are at TDC at same time. So watch your cam gears, and roll engine over till crank mark lines up and cam gears line up with marks. Not sure which cylinder will be on it's firing stroke at that point, but I think Maytag mentioned it's the #4 cylinder on the firing stroke at that point.
Any manual will have a good picture/diagram of the pulleys and marks.

[maytag]

Thanks for the answer, however it may be because I'm slow but I'm still confused. when replacing timing belt, tower cam seals and gears do I put 1 or 4 at tdc? For lining up the dots in gear with cam mark. if 4 is on exhaust stroke is 1 on intake, this would make timing 180 out?

Majicwrench is right on. this is a 180d crank. sometimes called a "single-plane" crank. Ferraris use it too. And Yamaha motorcycle's newest technology uses it too. basically: you have #1&#4 at exactly the same point in the stroke, together, at the same time. And #2&3 are similarly correspondent. However; you need to remember that your cam gears rotate at 1/2-speed. So the when you line-up all the timing marks (cam gears correctly aligned to their respective markers, and crank pointing to 0d / TDC mark), #4 is at the top of it's compression stroke. But the next time that crank mark comes around to Od / TDC, the cam gears will not be pointing at their marks, and the #1 cylinder will be at the beginning of its' compression stroke.

Does that help?

[joelbert2k]

I think Maytag finally got the right idea out. It can be confusing sometimes.
For reasons only the great Guido knows FIAT chose to put the cam timing marks at #4 TDC and not #1 like most others that I know of. (and by TDC I mean on the compression stroke, both valves closed)
So to further confuse things, you set the engine on #4 firing for the belt and and point the rotor at #4 cylinder when installing the distributor. For ignition timing you can hook your light up to either #1 or #4 plug wire.
Does that make sense?
Joel

[dutchdriver]

thanks , that does make sence now thanks for all the knowledge this site gives.