......AlexGS where are you?
Ha - thanks
Quite busy these days earning a dollar or two - only this week, I promise
I've never taken the turbo off an Uno Turbo, or the head for that matter. I think the turbo has a stabilising bracket to the block that would have to come off first. So my comments below apply to the other engines of this type (1116/1290/1299/1301/1372/1498/1580cc).
Head removal should be straightforward as Mark said, manifolds out of the way first. Cambox comes off to allow the head bolts to come out. Remember to slacken all the cambox bolts gradually - one is a different length (height)outside the 'circle' of the others - tucked in behind the cam pulley - don't forget it!
As you lift the cambox off, use a spare finger to push each valve bucket out onto the valve springs/caps - do not let the buckets fall out by themselves or they go everywhere - they are round, after all... if you mix them up, you create a lot of work later
Re-surfacing of the head may not be necessary - depending on how well the old gasket comes away and whether there seems to be any erosion around the 'fire rings'. Ensure only the lightest possible skim is taken... It's unlikely for the head to be warped, but if this is the case, bolt the cambox back onto the head and make sure the camshaft rotates freely. Speaking of which, I had one engine where the camshaft bearings were mysteriously tight - due to an oil varnish formed! Cleaned off with 'Scotchbrite' abrasive pads.
Valve stem seals - I find it's best to cut through the metal outer ring that makes each one such a tight fit on the valve guide. I use a small grinder on an electric 'Dremel'-type tool. I once thought I had the quick answer for removal - vise/mole grips - DO NOT do this as when you crush the top of the valve guide, it has to be drifted out and replaced - not very easy and you have to get another guide from somewhere. It pays to take a little longer on the removal and prevent such expensive remedial action... installing the new stem seals needs a 7/16" socket (or was it 5/16", I can't remember - one of those two).
Please use new head bolts - I find they are much easier (than old ones) to tighten to the correct torque + angle (check Haynes manual for sequence). And, it really ruins the job when you shear off a bolt in the block during the final tightening - that set me back several days!
On another engine, I had a blown head gasket after 5000km, which I put down to the re-used bolts needing 're-torquing' as the old-style non-stretch studs and nuts would have needed. The idea of the new-style bolts (with angular tightening) is that they stretch during installation to exert a constant compression to the head gasket and obviate the need for retorquing. That's why re-using them is a bad idea in my opinion because some of the 'stretching' has gone. But you're a mechanic, so I guess you know this already!
Oil the threads of the bolts and allow to sit for half an hour so as to drain off excess oil. I think it's 10Nm, then 30Nm (check this), then 90 degrees, then another 90 degrees. If you re-use old bolts, you may find the last 90 degrees to be almost impossible.
Setting the shims (mainly necessary after lapping or replacing valves) is quite a time-consuming task. Start by noting the thickness of each shim as you put the buckets into the cambox - write them in careful order...
The buckets can be persuaded to stay in the cambox if you smear some assembly lube on the sides of the bucket (I use 'oil stabiliser' or 'gearbox oil treatment') or even some bearing grease. This is so that as you lift the cambox onto the head, the buckets don't fall out.
If possible, get access to a collection of shims - about 20 will do, the more the merrier... They come in thicknesses from 2.80mm to 4.70mm. Most Uno engines seem to still have 'factory' shims of very similar sizes - 3.00, 3.05, 3.05, 3.10 etc!
If you have the special tool A60421, that speeds the job - because you can change the shims two at a time (the special tool depresses two buckets at once). The clearance you are aiming for is 0.40 inlet, 0.45 exhaust, plus or minus 0.04 or so.
Otherwise you can assemble, measure each clearance, check the written-down existing shim size and work out what shim is needed (some of these may be in use on other valves, which is another reason to write them all down while you have the buckets out).
Once you have worked out required shims for all valves, you can unbolt the cambox and change all the shims at once. So it IS possible to do the job without special tools, but you may have to repeat the exercise for the odd one or two that are still 'out' after your calculated adjustment. You have to be pretty precise with the measurements, accuracy to 0.02 or so, to allow for the 0.02 inaccuracy in the clearance measurement PLUS the 0.02 inaccuracy in the shim measurement... worst case this adds up to 0.04, which is your tolerance range. That's why the job can be time-consuming... sometimes it takes several goes to get each valve right, sometimes it's right first time.
Cambelt 'special tool' consists of two small bolts pushed into the holes in the tensioner, with a stout Phillips screwdriver threaded between them and used to lever the tensioner around a ring spanner on the 13mm nut in the centre.
Make sure to turn the engine over two turns by hand before rechecking timing and tension - please don't be tempted to start-up without doing this; I bent a valve this way once (belt not seated in all the teeth so not actually tensioned when it seemed to be).
If you have an engine with the distributor mounted on the block, note that there is no timing mark on the auxiliary shaft pulley - so you'll have to pull the distributor out of the block and re-set the timing.
A trap for mechanics from other makes: with the camshaft and crankshaft timing marks aligned, FIAT has the distributor timed on No. 4 cylinder (not No.1 as you might expect).
My experience is that it's easy to over-tension the cambelt - generally, there should not be a whining or a rumbling noise with the engine running. If there are such noises, back the tension off a teensy amount, turn engine back and forth to ensure belt is settled, run engine again.
The 'trade' rule of thumb is that the cambelt should just twist through 90-degrees on the longest run, when twisted with thumb and forefinger. I believe that 120-degrees is nearer the desired tension for the FIAT SOHC engine. I base this not only on the noises generated but also on the tension provided on early 128-X1/9 motors that had a spring-loaded tensioner (I think, the early Uno as well) - this spring was not actually all that strong!
While you have the cambox off, give some thought to replacing the camshaft oil seal (behind the pulley) - they harden and leak over time. The inside of the cambelt cover and condition of the old belt will give some idea of the severity of the leak.
At the other end, the distributor (on Mk1 Uno Turbo and Tipo 1.6) has a seal inside that hardens and leaks oil inside the distributor, filling up the distributor cap. It's a special size; FIAT part only. There's also an O-ring on the distributor body - this is a standard size (easily available) and cures any leak from outside the distributor.
I always use gasket sealant on the thin paper cambox gasket (the one between the head and the cambox) - Loctite 618 Master Gasket is my pick (not silicone). A new cam cover gasket is always worthwhile - no need for sealant on that one as it's thick and soft.
Also a good time to critique the thermostat before refitting - should be tight shut - cheap enough to replace if not (common failure that goes un-noticed).
I think that's all my hints, hope that keeps thepottleflump happy
-Alex
