blind folded
If you are asking about timing gears with a belt system, you have to line the timing marks up with the marks on the gears. If you want to know about chain gear alignment please re-ask with vehicle specifics and I can answer that also.
This is not the Yugo page, this is the Ford Escort page.
Remove the valve cover and line up the timing marks on the crank and both cam gears. Now remove the crankshaft pulley and the timing cover. Insert a pin through each cam just behind the gears to hold them in position for reinstallation. Loosen the belt tensioner bolt and remove the belt. Now reinstall the new belt. I usually remove the pin from the exhaust cam and turn the crank counterclockwise to pull the slack to the tensioner side. Now tighten the tensioner bolt and turn the engine over a few times then line up the timing marks again. That will ensure proper belt alignment and cam timing.
A timing mark is usually a white line on the timing belt to sync the firing of cylinders in an engine. You can see this line when the engine is turned off or with a timing light also a strobe light when the engine is running.
If the timing belt broke you probably got some bent valves. but as for puting the timing belt back on, there are marks on the outer edge of the cam and a indention on the valve cover behind it. line those up and on the crank gear blade there is a small v. line that up with the triangle on the engine- around the 10 o'clock position. then you will have to commpress the tensioner and use a small Allen wrench to hold it compressed. then install the timing belt and put the tensioner back and pull the pin. spin it over by hand and make sure the marks line back up
THERE ARE SMALL HOLES IN THE TIMING GEARS THAT LINE UP WITH MARKS ON THE FRONT OF THE HEAD. When the crank pulley is at TDC on the compression stroke, 'E' & 'I' on the camshaft sprockets should be at 12 o'clock.
Line up the marks on the gears with the off colored links on the timing chain.
To adjust the timing take off the timing cover,take off belt and then line up the marks on the timing gear.You will need a special tool to hold the gears if it is a DOHC(duel over head cam)
there are 2 marks on the gears you have to line them up
there is a line on bottom engine pully behind belt pulley and there are dots on the cam shaft gear's at the top line these up with the marks on engine
There should be markings on them. Make it so that they face each other. (well, that's on the Ford engines that I've worked on..... but those are ancient)
the Serena has different engines so depends on what engine yours has, the best way to get this right is to buy a belt from Nissan the timing marks are on the belt just line everything up