Technical 1.6 cambelt change - the detail

[Steely]

Right, just a quick one. ive changed 3 or 4 belts on mg/rover k-series engines up to now with the "tippex" approach,

Is there any reason why the same can't apply to the fiat 1.6 lump?


plugs out, pistons back to safe position then being marked up cams to belt and same with bottom crank? then duplicate the markings between old and new belt??

got the kit from fiat with jockey wheel, tensioner and belt,

any info greatly appreciated!

 

[Deckchair5]

Whilst you can undoubtedly do the job on a 1.6 that way it's probably not the best.The best by far is to use the proper cam aligning tools. The old belt has stretched you see by now and the cams go very slightly out of alignment. With the tippex method you just put them back in the wrong place again. The locking tools are not just locking tools, they are alignment tools and it's the one chance to get the cams back in the exact and correct rotational alignment.



This enables you to loosen and rotate the actual camshaft sprockets whilst keeping the cams still, in order to match the sprockets teeth to the new belt which you wouldn't dream of doing if you're doing the tippex method of just putting things back in the same place as they were

Does that make sense? For instance mine went in for cambelt change with quiet a nuisance low rev flat spot and when it came out the flat spot had gone as the alignment then was exactly correct
A lot of garages don't do it correctly and there's been a load of Stilo owners having probs after cam belt renewals and needing to go and get the job done properly

Crank pulley bolt is a bit of a bitch. I'd see if you can loosen that one first before you go too far. Easier if it's on a ramp

 

[alexGS]

Whilst you can undoubtedly do the job on a 1.6 that way it's probably not the best.The best by far is to use the proper cam aligning tools. The old belt has stretched you see by now and the cams go very slightly out of alignment. With the tippex method you just put them back in the wrong place again. The locking tools are not just locking tools, they are alignment tools and it's the one chance to get the cams back in the exact and correct rotational alignment.
...
This enables you to loosen and rotate the actual camshaft sprockets whilst keeping the cams still, in order to match the sprockets teeth to the new belt which you wouldn't dream of doing if you're doing the tippex method of just putting things back in the same place as they were

Doesn't make sense to me (I think it's a first for one of your posts, Decks!)

Suppose that the old belt has stretched and the cams go very slightly out of alignment. You mark these positions with Tippex. That means when you put the new belt on, the Tippex marks wouldn't line up exactly - BUT the cams would be in their original, correct, position again. It would be impossible to put them back in the same, wrong position unless the new belt was 'stretched' to the same extent as the old belt.

In reality I've yet to see this belt-stretching business. They seem to stay dead-accurate to me.

The one thing I would really suggest is turning the engine over by hand several times before even thinking about starting it, just to make extra-sure that the belt is seated and tensioned properly and that all pulleys are still close to their respective marks.

Cheers,
-Alex

 

[Deckchair5]

Yeah I know, i couldnt see how it all was necessary when I first encountered it but it sure makes sense now. It's why a lot of Stilos are coming away from garages after having a cambelt change with valve timing all over the place. I'll see if i can post up some piccies to explain later

 

[Deckchair5]

Ok Let's see if i can explain

Two things to appreciate first.
1 Belts do stretch, not by much but they do and it doesn't take much as we'll see to make big differences in the valve timing. That's why the recommended method of installing a new cam belt is to put it on maximum possible tension at the tensioner first, then rotate the engine a few times to straighten and stretch the belt and THEN set the tensioner to the correct tension. Then recheck the crank and cam positions again


2 Undeniably, if the 1.6 engine was running fine to start with and tippex marks are used to mark the crank and camshaft positions and if the marks are exactly the same when you finish the job then the engine will run the same as before.

So what goes wrong?

If we say there are 30 teeth to a cam sprocket then each tooth will be 360/30 degrees = 12 degrees. That means half a tooth out = 6 degrees error.

Ok so let's see what happens

You wind the new cambelt over the crank sprocket at the bottom and work your way anticlockwise up to the top right cam sprocket.

But the belt teeth and the sprocket don't quite line up. What are you going to do?

Not much choice, you have to move the whole camshaft with sprocket a fraction to align the sprocket to the belt. You didn't move it much, it's almost in line with your tippex marks, it looks ok, it's as near as you can get it but in the worst case scenario you're 1/2 a tooth out-6 degrees.
And the same thing could be happening with the remaining camshaft

The mistake is that you've moved the whole camshaft to align with the belt rather than keep the cam still and move the cam sprocket to align with the belt

In the best case scenario you have put the new belt on and aligned things exactly the same as the were. But if the camshafts were out of alignment by even a fraction to start with then they'll be out of alignment to the same amount again when you've finished as you have used the tippex marks to check that it is the same

Now take the approved method

The crankshaft is exactly at TDC


The cams are exactly in position


The cam sprockets have been rotated on their camshafts until they align perfectly with the belt and THEN tightened

Only now is everything guaranteed to be exactly as it should.

Mine had a sickly hesitation at low rev pick up- always at 1500rpm- bloody nuisance when crawling along in traffic. After a correctly carried out cambelt change and realigment all was as it should be

 

[minimad99]

Awesome as usual Decks!!

 

[Deckchair5]

Ah Good. Glad that makes sense.

The reality is that many garages do not double check the timing after doing the job as it takes a little extra time and patience but it would guarantee that all the timing is good. Often, the next job is waiting and the boss is breathing down their neck so out it goes for the customer to do the testing and they wonder why it's running like a bag of spanners

I think there's been at least 6 Stilo owners on here alone that have experienced post garage cambelt change running problems so the real numbers must be huge

Note this is only for the 1.2 1.6 and possibly 1.4 engines (haven't met one of those yet)

 

[Steely]

one question decks, i do agree with what you say but surely if the belt has stretched now, surely its either running slightly advanced or retarded on ignition and and fitting a new unstretched belt will bring it back to how it should be,

because as i see it if i lock the cams off and loosen the sprocket to align the teeth then surely its set up to the timing of the old belt,, which may have stretched,

im not doubting you just before i attempt anything eithe rwith or without timing tools id rather fully understand the theory, cheers!

 

[Deckchair5]

i do agree with what you say but surely if the belt has stretched now, surely its either running slightly advanced or retarded on ignition
not ignition but valve timing


because as i see it if i lock the cams off and loosen the sprocket to align the teeth then surely its set up to the timing of the old belt,, which may have stretched
Yes see item 2 up above. If you lock the cams from turning and loosen the cam sprockets then you can keep the valve gear timing the same as it is now, whether it's right or wrong.

But with "the tippex approach" and not allowing the aligning of the cam sprockets you're moving the valve gear to suit the belt which is very hit and miss

Be aware that if you loosen the cam sprockets and the cams move you're sunk and will have to get hold of the proper alignment tools

 

[Steely]

my approach on timing with tippex is to mark the tooth on the sprocket and the relative two teeth on the belt either side of the one i marked on the sprocket,, , same on both cams and crank, then duplicate the same marks onto the new belt,


the way I see it is the belt that was fitted to the stilo on the production line is the same spec as the one i have for replacement, so theoretically should be the same,

this is what i mean:

whats your thoughts??
how come this theory works on most other engines ??

 

[Deckchair5]

I can't see why you're marking the new belt, it's the relative positions of the 3 shafts that have to be aligned. The old belt is going in the bin and the new belt?-well it doesn't matter what marks you make on there.

It's good that you're intending to loosen the camshaft sprockets to align them with the belt BUT, as I've said, if the cams happen to rotate whilst you have the sprockets loose then you'll lose all your references and will need the proper tools to find them again. You just won't be able to check with tippex marks at the end whether everything is in the same alignment as when you started as the sprockets will have been moved

If you can lock the crankshaft AND lock the camshafts then you have every chance of things being the same at the end as when you started whether the valve timing was right or wrong.

 

[Steely]

No sorry decks, i think ive confused you there, im not loosening the cam sprockets,

marking the old belt so i can transfer it to the new belt when i put them side by side, and count the teeth,

im just struggling to understand why this engine is different, ive done cambelts on a modifed caterham, and 3 rover k-series lumps a 1.4 , 1.6 and 1.8.., and this works.... the relative markings are the same between the belts so it should work. in theory with the new belt fitted it should be in the same position as it was from factory ,

im not being naive or trying to be ignorant to what you say as im sure your right, i would just like to be able to understand it, and i cant... i dont know if im missing something or what??

cheers for the help anyway decks , it appreciated ,

 

[Deckchair5]

Ha! What part of post No 5 don't you understand?

The tippex method will work, the engine will work but whether the valve gear will end up correctly aligned or up to 1/2 tooth out (or more if you're careless) is a guessing game

That's why so many people picking up thier Stilos after a cambelt change end up taking them back to be done properly as "it's not running right"

 

[FIREsporting]

nice job lets hope he fit it ok

 

[cheapomulti]

well I changed the cambelt, tensioner and idler on my 1.6 16vlv multi yesterday using the age old tipex and tooth counting proceedure I've used this many times on YB's with vernier pulleys(you simply dont undo the pulleys/sprockets) .....no real problems on my multi except the bolts holding the cam belt cover on were seized solid ..took longer to get the cover off than changing the cambelt....had to chock the flywheel and use a 3/4 36mm socket to undo the nut for the aux drive pulley (note if you're doing this the nut has normal rotation IE lefty loosey righty tighty)
All sprokets were marked both in relation to the belt and in relation to each other and so was the old and new belt ....ALL the marks align perfectly after the belt change......

she runs/idles lovely (as she always has done)

I can see however that if you dont mark the new belt and count the teeth ...you're going to have to buy the proper tools which retail for ~£110-£140 depending on where you buy em....which lets face it is still cheaper than getting the job done at a stealership....so its not all bad which ever way you do it...

to add to the argument I've never seen a timing belt stretch buy any appreciable amount and we used gates belts at work on large servo motors which remain accurate to 1/100 of a degree even after many millions of rotations....I have seen them break and strip the teeth of off the belt though...

 

[Deckchair5]

Standard procedure when you install a cambelt is that you need to put the tensioner on maximum in order to stretch the belt and rotate the engine by hand for at least two revolutions. Then you you do the real job of making sure everything lines up again and set the tensioner to the correct tension

I've never seen a timing belt stretch buy any appreciable amount
You can't see a belt stretch but you'll hear many a stretched belt with a lot of squealing alternator belts at this time of year as the electrical load goes on to an old and stretched drive belt. Same thing with a cambelt, it stretches, that's why it's a a spring loaded tensioner in there, to take up the slack and retain the same tension as the belt stretches

If you've got the marks still all perfectly in line and the correct tension then the job is done

 

[cheapomulti]

the engine was rotated for a total of 12 times by hand, after all to make sure the pulleys align to each other not just to the belt you have to go through all 4 strokes !!!!!(only valid for Dohc 16vlv engines), so I checked the alignment 3 times in total.... this was the way I was taught at my main dealer (albeit non fiat) training.....many many years ago..
also one manufactuer quoted us a spec of less than 3mm stretch over our normal service life of our timing belts at work....thats after >75000000 cycles....I've seen more problems with tooth errosion on cheaper belts than strech...

Its nice to have some one with some knowledge to converse with ...whats your background...I'm guessing you were or are a mechanic or engineer ???

 

[Deckchair5]

I'm in lingerie actually.

Well no, that's just a hobby

Yes I used to get my hands dirty quite a lot but now i try to avoid it

 

[cheapomulti]

I'm in lingerie actually.

Well no, that's just a hobby

Yes I used to get my hands dirty quite a lot but now i try to avoid it

very good

 

[s31vyn]

Hi guys,

Im from South Africa, and the service here is out of this world expensive, if you convert our currency to yours, it turns out to about 350 quid, to do the cambelt at Fiat!

The belt one can get from a spares shop, but not the tensioner, how long does the tensioner usually lasts, or should I opt to get a new tensioner?

The cambelt kit alone, excluding labour is 160 pounds(converted from ZAR)

I have made up a set of tools to lock the cams (178d2 motor) based on the original camlocks Fiat uses!

Any help would be greatly appreciated!