Numbered items in the photo are:
- Factory/dealer timing reference tool (which you likely will not find anywhere at any price );
- Nut that secures the position of the tensioner bearing (arrow shows direction to slacken the belt tension);
- Tensioner spring anchor and bracket pivot bolt (the bolt thru the center of the spring itself is visible on the other side of the reference tool from here);
- Timing mark on crank pulley;
- Crank-timing reference pointer (you will find the equivalent of this on your belt cover or as a metal pointer bolted to the block);
- Aux shaft wheel timing mark.
Timing belt replacement is easy enough for the average shadetree mechanic -- BTDT myself, in the parking lot of my apt complex at the time! The only real tricks lie in knowing how to set the tensioner bearing, and how to line up the various timing marks on the cams, crank and aux shaft. To make things easier, before removing the old belt, you may want to remove the sparkplugs and gently turn the crank until things are lined up at or near the proper reference positions.
The cam wheels each have a small hole thru the flank, which should be aligned with a raised mark on the seal-carrier flange at the end of each cambox where the cams exit. This is easiest to spot looking from the (US) driver's side (gearbox/battery side) of the engine bay, sighting down the valley between the camboxes. In practice (thx to a tip from Haynes), I found the holes actually best lined up appearing to be tipped slightly together (towards each other and the centerline of the cylinder bores) WRT the marks on the cambox flange.
The crank pulley should have an obvious notch on the edge or a cast-in line on the flank, which should be aligned with the TDC mark on your belt cover or crank-timing pointers. Early engines had timing marks stamped into the belt cover at about the 1-2 o'clock position; later cars had a toothed metal pointer bolted to the block at about the 10-11 o'clock position. BTW, there are typically three crank-timing marks on that cover/pointer; the most-forward one is TDC and the others are -5 and -10 deg. BTDC (the latter being used for ignition advance timing-light reference).
The aux shaft wheel has a hole like the cam wheels (actually the very same part # as the exhaust cam wheel), but this one's a bit trickier, as there's no obvious mark to align with. That hole needs to fall on a line drawn between the aux shaft center and the bolt that goes thru the center of the tensioner bearing spring. I found it easiest to stick a small screwdriver bit thru that hole, so it was sticking out in view where I could sight down from the spring-mounting bolt above and line it up.
Now, the tensioner bearing. After you remove the old belt, be sure to test the bearing itself, see that it turns smoothly by hand with no apparent looseness nor coarseness to the motion. If you have ANY doubt that the bearing is sound, you WILL want to replace it now (as covered below). A typical twincam FIAT bearing is NOT the same as the Lancia shell with replaceable bearing cartridge, but a retrofit to the FIAT bearing will work if you also use a FIAT tensioner bracket. Substitute bearing cartridges of the right dimensions are available that will press into the Lancia bearing shell and do the job, but they are not as robust as the OEM split-center-race bearing, so any such substitute bearings should prolly be replaced with every belt change regardless of apparent condition. (As of this March 2017 edit, Midwest-Bayless in the US stocks the FIAT-style bracket and bearing as well as OEM Lancia-style bearings, so take your pick.)
Belt tension is not actually maintained by the tensioner spring, although the spring helps get the new belt taut to set the proper tension point initially, before you lock the bearing center firmly in place. There is a stud in the block that extends out thru the tensioner bracket and center of the bearing, then thru a stepped-flank washer that nestles into the bearing center and has a much larger center hole than the stud diameter, then thru a smaller washer with the proper ID, all held together with a nut. The wide hole in the stepped washer allows the rotating axis of the bearing to be adjusted WRT the stud/nut when that nut is loosened.
You may find it difficult to push the bearing back towards the slackened position while the spring is still engaged. I eventually gave up on that approach and just pried the hooked end of the spring out of the tensioner bracket that carries the bearing, loosened both the spring/bracket anchor bolt and bearing-center nut just enough to push the bearing back (you may want to take this opportunity to apply ample grease between those two washers on the bearing), then tightened the bearing-center nut to lock the bearing firmly in the slackened position and used a longish 13mm wrench hooked against the spring bolt to leverage the spring back into the tensioner bracket. You will want to leave the spring/bracket anchor bolt slightly loose for now, as the bracket will need to pivot on that bolt when you set tension on the new belt.
If you need to change the bearing, first unhook the spring and then completely unbolt the tensioner bracket by removing the bearing nut and anchor/pivot bolt (items 2 and 3 above), which should allow enough access behind the bracket plate for Vise-grip or similar pliers to grab the unthreaded shoulder of the remaining stud, to remove it from the block without damaging the stud threads. To extract the bearing from the bracket, you can simply hammer out the mounting boss from the center of the bearing -- e.g., using the male end of a 1/2" drive socket extension/adapter as a punch, with the bearing edges supported by the spread jaws of a bench vise. Use the vise, and/or a hammer against a large block of wood, to mount the new bearing.
Slipping the new belt on is fairly easy if your timing pointers are all lined up. You may need to use a 19mm wrench to jockey the intake cam ever so slightly to get the wheel and belt teeth lined up so you can slip the belt over the intake cam wheel last. Since the aux shaft turns rather freely on its own, you may need to re-align the aux shaft timing after the belt is on, but it should still be (barely!) loose enough to allow this. You may also find the crank pulley mark winds up slightly retarded (anticlockwise) from its alignment mark, but setting the belt tension should bring that back into line.
With the new belt in place and all shafts properly aligned, loosen the tensioner bearing-center nut gently to allow the spring to pull the belt taut. Leave that nut ever-so-slightly loose for now. Turn the engine gently by hand (clockwise looking at the crank pulley end) for at least two full crank revolutions. Then fully tighten the bearing-center nut to lock the bearing's rotational axis in place, and also tighten the spring/plate anchor bolt as well.
With any luck, you can now fire up your engine and enjoy!