Changing 348 cambelt - a how to guide.

Discussion in '348/355' started by agnello11, Jun 12, 2008.

  1. agnello11

    agnello11 Karting

    May 27, 2008
    This is the procedure i used for changing the cambelt on my 348. Obviously this is a 4 cam engine with all 4 cams driven off the same one belt which runs over two idler bearings, one of which is also the tensioner. The belt is driven by a sprocket run off the crankshaft via a chain inside the engine.
    You cannot use the belt replacement method of partially cutting the old belts on this engine as the drive sprocket edges do not allow you to slide the new belt on, so you have to use the correct full removal and replacement method. I haven’t covered replacing oilseals or verifying camshaft timing (degreeing cams) here as that is well covered elsewhere if you feel like going the whole hog, taking off the cam covers and checking that too (look here and here ) – this is just concerned with the most common job of a straightforward belt replacement.
    Ok, so this is a fair sized job but well within the scope of any reasonably competent home mechanic with access to a decent selection of tools.
    Whilst there is loads of debate over doing this engine in or out, i did it engine out because i wanted to inspect all the other parts and mess around with some other stuff too – so for the purposes of this write-up we are talking engine out.

    1 – remove the rear subframe / engine assy. (there is an excellent guide here:- Engine removal guide ) It is actually possible (and not that difficult) to get the engine and frame out and leave the A/C pump attached to the car if you don’t want to de-gas the aircon – just slacken and remove the belt, remove the lower mounting bracket bolts and the top tensioning / pinch bolt and the pump can be moved down off the engine, the electrical connector unplugged and the pipes wiggled past the top mounting bracket. It can then be held forward (under the fuel tank) and out of the way of the subframe as it is lowered out. Leave it attached to the car and aircon pipes, then remount it to the engine after the engine is reinstalled.

    Picture here Fig. 1
    Once out, the engine can stay in its frame and be worked on off the floor. Next, prepare the cambelt covers for removal clearing the ECU plugs and fuel pipes out of the way (inspecting for damage as you go). Undo the four allen-headed bolts holding each cam belt inspection cover on and remove. Then undo the several allen-headed bolts holding the front cam belt cover in place and remove. You can now see the belt, tensioners and the job in hand.
    Picture here Fig 2
    2 – this is where it gets important as we need to start referencing to make sure the belt is put back correctly and give us a datum to get back to if a camshaft partially rotates (which is quite likely) or we mess something up – don’t skimp on this, you won’t thank yourself if you do. First off we need to establish proper TDC (Top Dead Centre) on the firing stroke on no.1 cylinder as that is the position the engine will be placed in to change the belt. The marks on the engines aren’t great and it is good practice to establish they are right before relying on them. So turn the engine until no.1 is on the compression stroke and the piston is rising up the bore (easy to tell if you have the spark plug out and place your hand over the plug hole – you will feel the compression building up). Using a dial gauge (or wooden dowel etc.) watch for the piston to start topping out and then moving down – you just passed TDC. Wind the engine back (counter-clockwise) a half turn and then forward again, taking a reading on your gauge as the piston’s rise slows and it is approaching TDC – at this point make a suitable mark on your crank pulley with a pencil etc. in line with an indexable point. Carry on turning the engine clockwise until TDC comes and the piston starts declining again, watch your gauge for the same reading as your first one and at that point stop and make another mark on your pulley in line with the same indexable point – you now have two marks on the pulley – the mid point between the two is TDC, so mark that mid-point with a blob of paint or if it lines up with the factory centre punch mark you are good to go and you know TDC is correct (see fig. 5) . (the factory centre punch mark should line up with the centre line of the case right through the middle of the cam belt sprocket and water pump etc.).
    Picture here Fig 5
    Now look at the camshaft sprockets. You may be lucky and still be able to see the factory paint marks on the sprockets which should line up with eachother (fig. 4) along an imaginary line drawn through the centres of both camshafts in each respective bank (excuse the poor photo which is a little distorted). The marks should come together in the middle where the sprockets are closest together. If they are there and line up, great – skip ahead to marking the belt.
    Picture here Fig 4
    If you can’t see them, look at the backside of the camshaft sprocket and on the toothed rim you should be able to see a linear mark (like a cold chisel mark, see Fig 6) – each sprocket should have one although they can be very hard to see. These should be in line with the centreline of the camshaft longitudinally – an easy way to check is to put a 90 degree straight edge along the cast ridge on the cam cover which is also the centre line of the cam and see whether they line up (see Fig 7).
    Picture here Fig 6

    Picture here Fig 7
    If they aren’t there, can’t be seen or don’t line up, you will have to whip off the cam cover and check with the referencing notch on the cam shaft and bearing cap itself.
    OK, so now we should be very confident that we know where TDC is, we know where the camshaft marks are and we know how and where they all line up. As a final belt and braces approach, break out your tippex or paint pen and mark up your old cam belt – a mark for each cam sprocket and the drive sprocket and a mark so you know which side was which. With everything marked up and feeling confident that you know exactly how everything should line up and how the factory marks work, move on to the next step.

    3 – remove the crankshaft pulley nut (breaker bar or air impact wrench), you can lock the crank either on the flywheel end or easier with an old auxiliary drive belt wrapped around the pulley, pinched with some mole grips and secured to a rigid point.

    4 - The next stage is to take the old cam belt off, but double check your engine is still at TDC with your marks first – if it has advanced beyond TDC, you need to wind it back at least a quarter of a turn before TDC before turning clockwise again to hit your TDC mark. Happy? Good, now whip off the pulley, slacken the 17mm lock bolt on the cambelt idler which serves as the adjuster and nip it up in the fully retracted position. It should now be easy to remove the belt. Inspect all the drive flanges for signs of damage.

    5 – Removing the idler bearings. Assuming you are changing the idler bearings, now is the time to remove them. The left hand adjustable one is pretty easy, just undo the lock bolt and the three 13mm nuts that hold the mounting bracket on and it will wiggle out. The right hand one will need a puller – don’t try and do it without a puller! If you need more room, as you may find the jaws of your puller won’t fit in the gap between the cambelt cover and the back of the idler, you can create some more by taking off the mounting bracket (again undo the 17mm lock bolt, then the two nuts holding the bracket to the engine). Note that the right hand back half of the cambelt cover won’t come free from the engine unless you take the three lower allen-headed bolts out of the water pump and wiggle it past – more difficult on the aluminium covers than the plastic. When you use your puller, you should put something down the centre of the hole where the lock bolt came out for the puller to bear on (i turned down a bolt to slip in there) to avoid damaging the aluminium housing.

    6 - Re-mounting the idler bearings. Put the right hand one on first. You will need to press / tap it as far into the housing as you can and then snug it home with the lock bolt. Don’t be tempted to overtighten the bolt – it is going into a helicoiled aluminium engine block and you do not want to strip the thread. For the left hand tensioner idler, you can reassemble it all now and remount to the engine but it is a real fight to get the cam belt over it. Easier to clean all the parts, reassemble on the bench, then compress it to its maximum (hold one part in the vice or whatever) and tie it in its fully compressed position with a cable tie
    Picture here Fig 8
    Be careful with it from now on as you have just loaded a nice little weapon and should the cable tie slip or break it could fire parts of the assembly all over the shop! Put it to one side as we will install it after the new belt.

    7 – Check your water pump. Now you have your belt off this is the opportunity to check the state of the bearings in your water pump and do something about it if you feel uncomfortable. It should rotate smoothly with no gravelly feeling and slight drag and no / minimal play in the shaft when rocking the pulley.

    8 – Fitting the new belt. Now you can whack your new belt on. They don’t have a direction of rotation so just start threading it on. Doesn’t particularly matter how, just whatever works, but you must keep it tight in the direction of rotation. So there really shouldn’ t be noticeable slack between the drive sprocket, around the right hand idler bearing and to the right hand cam sprockets and same from the right hand cam sprockets via the water pump to the left hand cam sprockets. If there is slack it is likely you have got the belt one tooth out somewhere – check and double check. You may find you need to tweak camshaft pulleys to get the teeth to line up depending on how stretched your old belt was and how tight you can get the new belt, but just keep an eye on all your marks and work methodically and don’t panic if a camshaft jumps and partially rotates – just turn it back to line up your marks (bet you are glad you have those marks now ;-)) and work methodically. As a tip, i used a cable tie (circled in Fig 4 above) to hold the belt onto the outermost cam sprockets and stop it from jumping teeth and from the cams moving – just fed a cable tie through a hole in the sprocket and round the belt, no need to get it very tight it is only holding the belt down onto the cam sprocket teeth. I also used a cable tie to hold the belt around the drive sprocket. Now you can fit the tensioning idler – if you tied it back as above, it will be a simple matter of wiggling it into place so it is under the belt then cutting off the cable tie and nipping up the nuts on the mounting bracket. You can then fit but not tighten the 17mm lock bolt – making sure the little locating pin in the back of the idler bearing has found its slot on the engine block. With the new cambelt on, all your marks lining up and double checked and your idlers on, you can proceed to re-mount the crankshaft pulley.

    9 – Tensioning the cam belt. Cut off any cable ties you have put on and replace the crankshaft pulley and bolt (torque it up later). There are factory specs on belt tension using a special deflection meter, but the reality is that the tensioner spring sets the cambelt tension correctly. All you need to do is turn the engine clockwise two full turns and round to TDC and nip up the 17mm lock bolt and that is the tension set. As a last check before you put the cambelt covers back on, hook out your old belt and look at the marks you made on it, lining them up visually with the marks you made on the cam sprockets and drive sprocket – all line up? Good. Double check all the other TDC marks line up as they should and put the cam belt covers back on. Don’t forget the little belt runners at the top – these don’t touch the belts and should be set with a clearance between the running face and the belt of about 1mm. Put the inspection covers back on. Torque up the crankshaft bolt, check your work and you are done! Torque settings should be available in the workshop manual. Not that difficult was it...... feel free to add any tips or corrections or addn. info. below.
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  3. PAP 348

    PAP 348 Moderator
    Moderator Owner

    Dec 10, 2005
    Mount Isa, Australia
    Full Name:
    Welcome to Fchat Agnello. :):)

    Nice first post too. ;);)
  4. BT

    BT F1 World Champ
    Lifetime Rossa

    Mar 21, 2005
    FL / GA
    Full Name:
    Bill Tracy
    Great info, thanks for taking the time to write it up!
  5. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    This is a very imprecise method frought with many potential problems. Sometimes you you are the windshield and sometimes you are the bug.
  6. agnello11

    agnello11 Karting

    May 27, 2008
    Could you expand on that FBB? I respect your opinion having read many of your write ups and would value your input - if there is stuff in the above you feel should be changed then chip in. Part of the reason i wrote it up was to try and get at least something of a guide together, so if we all added our experience we would end up with a dependable step by step approach that anyone confident to have a go can follow.
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  8. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    No disrespect intended first off. These issues have been discussed here many times including the 308 board where the talk of those dreadful camm locks are discussed. They all think I'm nuts over there. You see the main issue is that you can run a chevy on just about anything and just about pour sand in the motor and the thing will still run. The tolerance for error with ferraris are smaller. Extra precision pays dividend in resale value, longevity, and performance. If one does not have the technical understanding to know where to shortcut then one should follow directions precisely because some things left out may only seem insignificant due to ignorance. That ignorance is ok if the tolerance is wide. If not one encroaches on value, longevity and performance. You fingered my 2 threads regarding cam timing and cam set-up. The reasons for the threads and the methods used have a method to the madness. An example is that if you do not unlock cam cogs while tensioning belts you have just built-in slack in your timing suystem and your timing is just off...period. Again its the tolerance thing. Its your car so you can do your own thing and its your right. Just don't be surprised when shortcuts become the industry norm and thus the resale values of the cars drop. You will pay one way or the other. I'd rather pay upfront and get the performance and lonevity too.
  9. troy_wood

    troy_wood Formula 3

    Apr 28, 2007
    Nova Scotia, Canada
    Full Name:
    Troy Wood
    This thread is really interesting - very helpful in terms of understanding what is expected as a ferrari DIY'er. Helpful because Agnello has given a really great overview of an engine-out belt change and FBB has qualified the given specification by emphasizing the seemingly small details that really do some heavy lifting in terms of value, longevity and performance. I am a new 348 owner and am gearing up to do my 30k major. I personally really appreciate reading as many posts of the major I can - reading the procedure from many unique points of view helps me synthesize and clarify my own interpretation of what is going on. FBB's point will serve as constant reminder to me to be weary of the things that I dont-know-I-dont-know versus the things I know-I-dont-know.

    The lesson of this thread is golden!

    Just thought I'd toss in my 2 pennies.
  10. Night life

    Night life F1 Veteran
    Rossa Subscribed

    Dec 1, 2007
    The city that rhymes with fun in Canada
    Full Name:
    Roberto Giannini
    :eek: Holy first post Batman...:eek:

    Maaaaaaaaaaaaaaaan that was pretty damn good.

    Now what are you gonna do for a follow up engine mods...;)

    Nice to have you on board.

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