Ok. Hope I'm not going to get too technical now. The reason why they want you to slacken that cam pulley bolt is because it allows the engine to be timed absolutely spot on for the new belt. However I've done a considerable amount of checking up on belt manufacture and the tolerances are very tight indeed so you can effectively say that the dimensions of one new belt compared to another new belt is gong to be identical - certainly so close that it's going to make sod all difference to this relatively agricultural old engine design.
Next thing to consider is that the timing tools lock the cam and crankshaft in the position they take up when the belt is fully tightened so it's going to be IMPOSSIBLE to correctly fit the new belt with the cam and crankshaft locking tools in place unless you slacken the cam pulley bolt. The best you'll achieve is with the belt one tooth, and often two teeth, retarded. You just can't get the belt over the sprocket teeth with both locking tools in place. - In effect you're trying to get it over the teeth with it fully tensioned on the right run of the belt, isn't going to happen. This is why they want you to slacken the cam pulley bolt. The cam pulley on these engines is not keyed so if you slacken that bolt the pulley is free to spin on the front of the camshaft. Of course as soon as you do then the timing is lost and you must have the locking tools to get the cam/crank relationship correct. So, with cam sprocket bolt slackened (only needs to be about half a turn, just enough to let the pulley spin unimpeded) and with both crankshaft "dumbell" locking tool and the angled camshaft locking tool in the slot in the "backend" of the camshaft you'll now find it easy to fit the belt. You just need to get it over the teeth on the crankshaft pulley, waterpum pulley and camshaft pulley. You're not interested in exactly which teeth at this point or whether the cam pulley is even in the same place it was when you slackened it's retaining bolt.
Now you've got the belt fitted and the new tensioner bearing in place carry out the belt tensioning procedure (depends on whether you've got a "Manual" or Automatic tensioner but I'd bet on it being a spring loaded automatic type on an engine with a VVT cam pulley. So, Ok, carry out the tensioning and you'll see it drags the cam pulley round anticlockwise a wee bit as the belt tension increases. Now, with the belt fully tensioned, the timing is correct and all you need to do is tighten the cam sprocket retaining bolt up again. It's very tight so don't have the cam locking tool in place when you do this or it's likely to either break the tool or knock a lump out of the slotted end of the camshaft. You'll need to hold the camshaft and stop it from rotating in some way (spanner or grips or ?) and there's a wee block which is part of the timing kit which screws into the front of the head ans locks the pulley. Maybe now you understand why you'll never be able to get a new belt lined up with the locking tools in place.
However, having said all this, I'm a great believer in "letting sleeping dogs lie" especially when it involves very tight fixings like that cam pulley bolt. So, here's how I do them and it doesn't usually involve slackening that bolt.
If this is an engine you've never worked on before then there is one big unknown and that is to do with that camshaft pulley. The question you need to be able to answer is "Has some numpty been in there before you and disturbed it and then retightened the securing bolt with the timing incorrectly set"? You can almost certainly say that if this is it's first belt since leaving the factory then it's going to be fine but it doesn't hurt to check anyway. On older cars, where this may well be it's second, third, etc belt then you need to check, for which you'll need the kit of crankshaft and camshaft locking tools. So, whip off the cam cover and gently rotate the crankshaft until the camshaft locking tool can engage the slot in the back of the camshaft - it's slightly offset so only fits properly in one position. Now offer up the crankshaft "dumbell" locking tool and, if all is well, the 3 pulley bolts and the one on the end of it's arm should be able to be screwed in without too much "jiggling".
If all the above has happened then you can say with absolute certainty that the cam pulley is correctly timed to the camshaft and you can, for now, forget about slackening it's retaining bolt, Phew! At this point, if the timing tools didn't line up you're going to have to slacken that cam sprocket retaining bolt and set it up correctly using the locking tools. However, assuming it did all line up, at this point I like to tippex mark the top and bottom pulleys and the nearest point on their casings, just to give me a reference point if everything goes **** up! - but it never has so far! Now you can slacken the tensioner and remove the old belt - both locking tools still in place - change the water pump (I always do this) and remove the old tensioner and loosely fit the new one. Now to fit the new belt. Starting with the crank pulley feed the belt into the teeth and push a wee piece of wood in between the back of the belt and casing so it doesn't come out of mesh with the teeth. Then on up round the water pump, keeping enough tension on the belt to keep it engaged with the teeth and lastly up to the camshaft pulley where you'll find Tarrah! the teeth on the bloody belt won't quite engage with the teeth on the pulley. They would if you could just, ever so slightly, stretch the belt. But these belts don't stretch (wouldn't be any use if they did) and this is the point at which people make the "fatal" mistake. they settle for getting the nearest tooth to engage with the cam pulley which is actually now setting her up one tooth RETARDED - maybe two or three if you're not too particular! The problem is that with both cam and crankshaft locked with the tools the positions of these pulleys is that when the belt is fully tensioned. You've no hope of getting the belt to engage correctly. The answer is very simple. With the camshaft tool still in place - thus locking the camshaft - take the wee bolt out of the end of the crankshaft dumbell locking tool (not the 3 bolts holding it to the crank pulley - and turn the crankshaft very slightly anticlockwise. I find about half a tooth is usually plenty. Now you'll find you can get the teeth on the belt to engage with the cam pulley and once you've got it settled on the cam pulley you can gently turn the crank pully back clockwise and you'll find the wee bolt pops back into it's hole very happily. Now, keeping an eye on the belt to be sure it's not jumped any teeth, apply some tension with the new tensioner and lock it off. Next remove all the locking tools and rotate crankshaft two turns until the cam locking tool can be dropped back into place whereupon you should find the crank locking tool is also lining up. Finally do the "official" tensioner tightening procedure, rotate the crank a few times and I then like to pop the timing tools back on "just to be sure" By the way, taking the plugs out will make all this turning over of the engine a lot easier and, of course, you'll be feeling for any resistance to turning which might indicate piston to valve contact and it's far easier to feel this when the plugs are out.
I've done a number of these using this method now, including my boy's 2014 1,4 8valve VVT Punto and our own 2010 Panda 1.2 8 valve which is not VVT and had no problems. what's more non of these vehicles needed a phonic wheel relearn! which I'm convinced is because the cam pulleys were never slackened which, together with the strict quality control on the cam belts, ensured no detectable change in angular displacement between the cam and crank sensors being observed by the engine ECU. All these vehicles are driving beautifully.
Pay attention to the first check with the timing tools though. if, with the old belt fitted, you can't get the timing tools to line up then this would indicate that the cam pulley is not locked off in the correct timing position and then you will need to slacken the cam pulley bolt and do the belt change by the "official" method. You may be interested to know I've asked around all the wee garages where I'm a "known face" and pretty much all of them do not slacken the cam pulley bolt. Also I've not so far come across one where the timing needed to be reset by slackening the cam pulley retaining bolt. I think slackening that bolt and the difficulty of holding the shaft immobile when it comes to retightening it - and it's TIGHT - is what introduces the angular irregularity into the equation and subsequently requires a Phonic wheel relearn to be required? I've not yet had to do a relearn on any I've done.
Hope that's helpful? and I'm now going to enjoy all the comments you're all going to rain down upon my head!
