Beta timing belt change procedure & tips
I was going to post this in reply to another thread, but decided it should occupy its own thread as an easier-to-find future reference for others. You will want to refer to this pic (click to enlarge) as a reference for changing the timing belt, and for following my descriptions/tips below:
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 and tensioner plate anchor/pivot bolt (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. 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, but good luck finding a new one (these are not the same as a typical FIAT bearing, tho' I hear a retrofit may be possible, perhaps using a FIAT plate?). Substitute bearing cartridges of the right dimensions are available that will press into the shell and do the job, but they are not as robust as the NLA split-center-race OEM bearing, and such substitute bearings should prolly be replaced with every belt change.
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 firmly in place. There is a stud in the block that extends out thru the tensioner plate 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 plate that carries the bearing, loosened both the spring/plate 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 plate. You will want to leave the spring/plate anchor nut slightly loose for now, as the plate will need to pivot on that bolt when you set tension on the new belt.
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.
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 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!
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This should be tightened before any movement of the belt and then loosened and retightened as you move the belt between coged pulley;s This is documented in Lancia Fiat manual. If you leave the tensioner loose as you rotate, you will not be properly tensioning the belt. 
Originally Posted by SubGothius
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