Oh dear, sorry, I did say I'd be back with more on this didn't I?

First thing I should say is that I found MES nothing like as easy to get working as my other program - VCDS, or VAG-COM (for my SEAT/SKODA vehicles) as it was called when I bought it - The VAG-COM was a matter of simply uploading and away I went. With MES you have to tell the computer how to communicate with its interface. I won't go into the fine details but I would say that the biggest thing to do is read the installation instructions very carefully and if you still can't get it to "go" there are many on here who can, and will, help also lots of "stuff" on line. The MES is not as "powerful" a tool as VAG-COM but probably lets you do pretty much anything the home mechanic might want to do and is considerably easier to use than the VAG-COM is

So now, how did all this "Phobic" learning stuff go? (I just love your, I presume unintentional, slip which turned "Phonic" into "Phobic". In my opinion most appropriately)

I finally got round to actually doing the belts on our Panda and my boy's Punto in June 2018 and I made several posts about it all at the time. I did the Panda first with the Punto just a week or so later. Both engines are 8 valve but the Panda has a solid cam sprocket whereas the Punto's is the VVT type. Although I've done many many cam belts I'd never before done one with a VVT pulley and there were aspects of it I was worried about (as it turned out needlessly- it was no more complicated to do than the solid sprocket) As both engines are virtually identical in every other respect, I decided to do the Panda first.

I'd read accounts of how tight this bolt is and the trials and tribulations some people have had undoing and then retightening them. So I bought the Haynes manuals for both cars and noticed that they were both recommending that this sprocket bolt be slackened. I had read of this becoming a quite common feature of more modern engines but hadn't done one yet - so more uncertainty and and "worry" in my mind. Then I started really thinking about this. Looking at the older cars I typically work on, the crankshaft and camshaft sprockets are typically located to their shafts with a key and slot of some sort (as in woodruff key) so the relationship between the sprocket and shaft is "fixed". Having built up a small number of engines where maximum performance was the aim I have "dialled in" performance cams using offset keys/dowels to get things absolutely perfectly aligned. Having a cam sprocket that can be tightened up in an infinitely variable number of positions would allow the same degree (pun not intended!) of accuracy, but for a standard "road" engine? I don't think you really need this. Arguably diesels are a wee bit different kettle of fish but these are really quite basic petrol engines in our cars. I briefly wondered if it was because of manufacturing differences in the belts but,from all I've been able to read about them these belts are manufactured to a very high degree of accuracy so I doubt if that's the reason. Accounts I've read detail how it's more difficult to fit the belt without slackening this bolt as the belt is difficult to get over the teeth with both sprockets (cam and crankshaft) locked? Ok, I've had that in the past and it's not proved insurmountable. So I checked the Haynes manuals and the torque figure for the bolts are indeed "tight" (by the way, Haynes quote 120 nm for your 16 valve engine). I would reiterate the advice to be very careful not to snap the locking tool - which might well result in damage to the cam too.

I've learned in the past that tight bolts seem to "grow" together with the component they are fixed to so undoing then invariably takes quite a lot more force than their quoted tightening figure. So, if I'm going to be undoing these I'm betting they are going to put up a fair fight - as confirmed by many posts I've read. Then, because I was reading lots of "stuff" about doing cam belts on these engines, I started picking up on the phonic wheel "thing". So what is it? Well, I think you probably know this but for those who are not so enlightened, the crankshaft pulley (the one that drives the fan belt) has "teeth" all round the outside of it and a sensor which sits opposite them on the front of the engine. This type of pulley is called a "Phonic Wheel" and, together with the sensor signal, allows the ECU to know exactly where the pistons are on their strokes. (Fiat seem to also call ABS sensors "Phonic" - same principal I suppose?) The cam has a similar set up which allows the ECU to decide which cylinder to send the spark to (remember the crank rotates twice for every one rev of the cam so the crank sensor can't sort out which cylinder to fire all on its own) Oh well, all right, you can have wasted spark designs which do this but let's keep it simple.

Anyway, What's this Phonic wheel problem all about? Well, the ECU learns (is taught by a Phonic Wheel learn) the relationship between the crankshaft position and camshaft position sensor signals. So, for instance, as the Phonic wheel on the crank causes it's sensor to send the signal (caused by a tooth variation on the wheel) which indicates TDC to the ECU, it - the ECU - will expect to be seeing a corresponding signal from the cam sensor. If that signal arrives at a different relative time (number of degrees of crank revolution) to what it's expecting - and, apparently only a very small variation is needed - it will flag up a DTC (diagnostic trouble code) and illuminate the EML (engine management light) on the dashboard. By the way, people report that when you interrogate the ECU (read the codes) you will often find a diagnosis of "missfire" recorded which can lead you off on a merry, and expensive, wild goose chase!

So, I was thinking, if you slacken that cam sprocket bolt I'm guessing you're very unlikely to be retightening it with the pulley in exactly the same position relative to the cam itself? This may be why the Phonic wheel relearn is said to often be needed? Then, when asking around, I found most of the small workshops I was speaking to, but not all, said they would not slacken that bolt and were not aware of any problems caused.

I thought about all this for quite a while before getting stuck into Becky I could find no info that her belt had ever been done (and later, when dismantling the old belt I became even more sure that this was her first belt since new) and decided to buy the timing tools, use them to check the position of the crank/camshaft before dismantling the belt and then checking the whole lot again after reassembly but to actually do the belt change by the "tippex" method (which is all detailed in those posts) and NOT slacken the sprocket bolt. (I'm a great believer in letting "sleeping dogs lie") My thinking being that the new belt would be, effectively, identical to the one I was taking off and so the only thing which might cause a variation in relative sensor signal would be wear in the old belt compared to the new and I think that would be negligible (the old belt was a genuine Fiat/Lancia belt and I used one of my favourite "Gates" kits.

Doing the actual job only really threw up two problems. First off was getting the engine mounting block off the front of the engine due to the lower two bolts being quite difficult to access. But this was just a simple access "ingenuity" problem which is faced in many different aspects in many different vehicles so solvable with thought and the right tools. The other was that the new cam belt didn't want to go over the cam sprocket teeth. I should explain that I decided to leave the timing tools in place - they had dropped into place very easily which indicated that the timing was correct to start with - even though I didn't slacken the cam sprocket bolt "just in case" and with the two pulleys effectively locked to the engine I just couldn't get the belt teeth over the sprocket teeth! This would not have been a problem if that bolt were slackened because the pulley would be free to turn on the end of the camshaft, but the problem was very simply solved by removing the single locking screw form the end of the crank locking tool and turning the crankshaft back by about half a tooth. The belt then slipped on very easily. When the job was finished, after several rotations of the engine and with the tensioner correctly set, I rechecked the timing by reinstalling the crank and cam locking tools. They just slid into place very nicely indicating that the relative crank/cam positions were spot on. The car's now been running since then, June 2018, without any indication of a problem. ie. no EML and running well. It runs around the town and goes out into Midlothian on the bypass and country roads and all is well. I mention this because people report that their EML didn't start flashing, after a cam belt replacement, until the first time they took a trip on a "fast" road. I'm guessing the ECU needs to see the signals generated at higher revs for a short sustained time for it to register?

The story with the Punto is effectively identical but, although I checked the timing with the tools before I started I actually left them off whilst changing the belt then rechecked again when I'd finished. I wondered if the variator sprocket on the cam would be a problem because I didn't really know at that time what was going on inside it and wondered if backlash might be introduced when oil pressure wasn't acting on it? However it's obvious that it has a strong spring inside it which holds the outer and inner sprocket parts in a resting position. So, from the point of view of doing this job the two sprocket designs behave the same - the VVT sprocket can be treated as if it's solid. The Punto does much more driving on the city bypass than our wee Becky so, if there was a problem with this method, might be expected to have flashed up a problem more quickly?

So, based on my experience with both these engines, I would say that you can do the job without slackening the cam sprocket bolt. However I don't think you should do it without the tools as you need to check, using the tools, "just to be sure". Without the tools you are relying on the pulley having been tightened in the right position by whoever did it before you. If this is it's first belt change since new then you're probably pretty safe - Hopefully the factory got it right after all! - but if it's an older car, where maybe someone less diligent has been in there before you, the timing could well be out. If a Phonic wheel relearn was then performed with this (perhaps "almost right" setup) the ECU would assume that things were all right so wouldn't be flagging up the EML but you would be loosing performance and fuel consumption etc.

Wow! think that could be my longest one off post? So, in the end, yes I got the MES working by going back - about 3 times at least - over the installation instructions and properly understanding what was required. Once installed correctly it's been a breeze to use. I didn't need to do a Phonic wheel relearn on either vehicle because the EML never lit off and the cars are running as well as ever. My overall conclusion must be that slackening that bolt is recommended because it will ensure that every time the job is done the timing will end up spot on when you've finished but the accuracy with which modern belts are made means that you really can do it by the tippex method with confidence AS LONG AS NO-ONE HAS MESSED IT UP AT THE LAST CHANGE. So, if it's an engine you're not familiar with you're going to need the timing tools.

Hope you haven't fallen asleep or slit you throat by now? I remember being quite unsure about all this when I first heard about a Phonic Wheel Relearn but it turns out to be a quite simple procedure if needed - Download the free version of MES, Find your vehicle in the list of models and run it in Simulate mode. Not all models even need a Phonic wheel relearn! Trying the simulation for your model will quickly reveal this because if it's not needed it won't even appear as an option!

Have fun and good luck.
Jock

PS I check my laptop most mornings and evenings so feel free to ask questions or PM me if you want.

Oh dear, sorry, I did say I'd be back with more on this didn't I?

First thing I should say is that I found MES nothing like as easy to get working as my other program - VCDS, or VAG-COM (for my SEAT/SKODA vehicles) as it was called when I bought it - The VAG-COM was a matter of simply uploading and away I went. With MES you have to tell the computer how to communicate with its interface. I won't go into the fine details but I would say that the biggest thing to do is read the installation instructions very carefully and if you still can't get it to "go" there are many on here who can, and will, help also lots of "stuff" on line. The MES is not as "powerful" a tool as VAG-COM but probably lets you do pretty much anything the home mechanic might want to do and is considerably easier to use than the VAG-COM is

So now, how did all this "Phobic" learning stuff go? (I just love your, I presume unintentional, slip which turned "Phonic" into "Phobic". In my opinion most appropriately)

I finally got round to actually doing the belts on our Panda and my boy's Punto in June 2018 and I made several posts about it all at the time. I did the Panda first with the Punto just a week or so later. Both engines are 8 valve but the Panda has a solid cam sprocket whereas the Punto's is the VVT type. Although I've done many many cam belts I'd never before done one with a VVT pulley and there were aspects of it I was worried about (as it turned out needlessly- it was no more complicated to do than the solid sprocket) As both engines are virtually identical in every other respect, I decided to do the Panda first.

I'd read accounts of how tight this bolt is and the trials and tribulations some people have had undoing and then retightening them. So I bought the Haynes manuals for both cars and noticed that they were both recommending that this sprocket bolt be slackened. I had read of this becoming a quite common feature of more modern engines but hadn't done one yet - so more uncertainty and and "worry" in my mind. Then I started really thinking about this. Looking at the older cars I typically work on, the crankshaft and camshaft sprockets are typically located to their shafts with a key and slot of some sort (as in woodruff key) so the relationship between the sprocket and shaft is "fixed". Having built up a small number of engines where maximum performance was the aim I have "dialled in" performance cams using offset keys/dowels to get things absolutely perfectly aligned. Having a cam sprocket that can be tightened up in an infinitely variable number of positions would allow the same degree (pun not intended!) of accuracy, but for a standard "road" engine? I don't think you really need this. Arguably diesels are a wee bit different kettle of fish but these are really quite basic petrol engines in our cars. I briefly wondered if it was because of manufacturing differences in the belts but,from all I've been able to read about them these belts are manufactured to a very high degree of accuracy so I doubt if that's the reason. Accounts I've read detail how it's more difficult to fit the belt without slackening this bolt as the belt is difficult to get over the teeth with both sprockets (cam and crankshaft) locked? Ok, I've had that in the past and it's not proved insurmountable. So I checked the Haynes manuals and the torque figure for the bolts are indeed "tight" (by the way, Haynes quote 120 nm for your 16 valve engine). I would reiterate the advice to be very careful not to snap the locking tool - which might well result in damage to the cam too.

I've learned in the past that tight bolts seem to "grow" together with the component they are fixed to so undoing then invariably takes quite a lot more force than their quoted tightening figure. So, if I'm going to be undoing these I'm betting they are going to put up a fair fight - as confirmed by many posts I've read. Then, because I was reading lots of "stuff" about doing cam belts on these engines, I started picking up on the phonic wheel "thing". So what is it? Well, I think you probably know this but for those who are not so enlightened, the crankshaft pulley (the one that drives the fan belt) has "teeth" all round the outside of it and a sensor which sits opposite them on the front of the engine. This type of pulley is called a "Phonic Wheel" and, together with the sensor signal, allows the ECU to know exactly where the pistons are on their strokes. (Fiat seem to also call ABS sensors "Phonic" - same principal I suppose?) The cam has a similar set up which allows the ECU to decide which cylinder to send the spark to (remember the crank rotates twice for every one rev of the cam so the crank sensor can't sort out which cylinder to fire all on its own) Oh well, all right, you can have wasted spark designs which do this but let's keep it simple.

Anyway, What's this Phonic wheel problem all about? Well, the ECU learns (is taught by a Phonic Wheel learn) the relationship between the crankshaft position and camshaft position sensor signals. So, for instance, as the Phonic wheel on the crank causes it's sensor to send the signal (caused by a tooth variation on the wheel) which indicates TDC to the ECU, it - the ECU - will expect to be seeing a corresponding signal from the cam sensor. If that signal arrives at a different relative time (number of degrees of crank revolution) to what it's expecting - and, apparently only a very small variation is needed - it will flag up a DTC (diagnostic trouble code) and illuminate the EML (engine management light) on the dashboard. By the way, people report that when you interrogate the ECU (read the codes) you will often find a diagnosis of "missfire" recorded which can lead you off on a merry, and expensive, wild goose chase!

So, I was thinking, if you slacken that cam sprocket bolt I'm guessing you're very unlikely to be retightening it with the pulley in exactly the same position relative to the cam itself? This may be why the Phonic wheel relearn is said to often be needed? Then, when asking around, I found most of the small workshops I was speaking to, but not all, said they would not slacken that bolt and were not aware of any problems caused.

I thought about all this for quite a while before getting stuck into Becky I could find no info that her belt had ever been done (and later, when dismantling the old belt I became even more sure that this was her first belt since new) and decided to buy the timing tools, use them to check the position of the crank/camshaft before dismantling the belt and then checking the whole lot again after reassembly but to actually do the belt change by the "tippex" method (which is all detailed in those posts) and NOT slacken the sprocket bolt. (I'm a great believer in letting "sleeping dogs lie") My thinking being that the new belt would be, effectively, identical to the one I was taking off and so the only thing which might cause a variation in relative sensor signal would be wear in the old belt compared to the new and I think that would be negligible (the old belt was a genuine Fiat/Lancia belt and I used one of my favourite "Gates" kits.

Doing the actual job only really threw up two problems. First off was getting the engine mounting block off the front of the engine due to the lower two bolts being quite difficult to access. But this was just a simple access "ingenuity" problem which is faced in many different aspects in many different vehicles so solvable with thought and the right tools. The other was that the new cam belt didn't want to go over the cam sprocket teeth. I should explain that I decided to leave the timing tools in place - they had dropped into place very easily which indicated that the timing was correct to start with - even though I didn't slacken the cam sprocket bolt "just in case" and with the two pulleys effectively locked to the engine I just couldn't get the belt teeth over the sprocket teeth! This would not have been a problem if that bolt were slackened because the pulley would be free to turn on the end of the camshaft, but the problem was very simply solved by removing the single locking screw form the end of the crank locking tool and turning the crankshaft back by about half a tooth. The belt then slipped on very easily. When the job was finished, after several rotations of the engine and with the tensioner correctly set, I rechecked the timing by reinstalling the crank and cam locking tools. They just slid into place very nicely indicating that the relative crank/cam positions were spot on. The car's now been running since then, June 2018, without any indication of a problem. ie. no EML and running well. It runs around the town and goes out into Midlothian on the bypass and country roads and all is well. I mention this because people report that their EML didn't start flashing, after a cam belt replacement, until the first time they took a trip on a "fast" road. I'm guessing the ECU needs to see the signals generated at higher revs for a short sustained time for it to register?

The story with the Punto is effectively identical but, although I checked the timing with the tools before I started I actually left them off whilst changing the belt then rechecked again when I'd finished. I wondered if the variator sprocket on the cam would be a problem because I didn't really know at that time what was going on inside it and wondered if backlash might be introduced when oil pressure wasn't acting on it? However it's obvious that it has a strong spring inside it which holds the outer and inner sprocket parts in a resting position. So, from the point of view of doing this job the two sprocket designs behave the same - the VVT sprocket can be treated as if it's solid. The Punto does much more driving on the city bypass than our wee Becky so, if there was a problem with this method, might be expected to have flashed up a problem more quickly?

So, based on my experience with both these engines, I would say that you can do the job without slackening the cam sprocket bolt. However I don't think you should do it without the tools as you need to check, using the tools, "just to be sure". Without the tools you are relying on the pulley having been tightened in the right position by whoever did it before you. If this is it's first belt change since new then you're probably pretty safe - Hopefully the factory got it right after all! - but if it's an older car, where maybe someone less diligent has been in there before you, the timing could well be out. If a Phonic wheel relearn was then performed with this (perhaps "almost right" setup) the ECU would assume that things were all right so wouldn't be flagging up the EML but you would be loosing performance and fuel consumption etc.

Wow! think that could be my longest one off post? So, in the end, yes I got the MES working by going back - about 3 times at least - over the installation instructions and properly understanding what was required. Once installed correctly it's been a breeze to use. I didn't need to do a Phonic wheel relearn on either vehicle because the EML never lit off and the cars are running as well as ever. My overall conclusion must be that slackening that bolt is recommended because it will ensure that every time the job is done the timing will end up spot on when you've finished but the accuracy with which modern belts are made means that you really can do it by the tippex method with confidence AS LONG AS NO-ONE HAS MESSED IT UP AT THE LAST CHANGE. So, if it's an engine you're not familiar with you're going to need the timing tools.

Hope you haven't fallen asleep or slit you throat by now? I remember being quite unsure about all this when I first heard about a Phonic Wheel Relearn but it turns out to be a quite simple procedure if needed - Download the free version of MES, Find your vehicle in the list of models and run it in Simulate mode. Not all models even need a Phonic wheel relearn! Trying the simulation for your model will quickly reveal this because if it's not needed it won't even appear as an option!

Have fun and good luck.
Jock

PS I check my laptop most mornings and evenings so feel free to ask questions or PM me if you want.

ooooops! why did that post a duplicate? probably something "silly" I did. Sorry folks.

Pugglt Auld Jock said:

ooooops! why did that post a duplicate? probably something "silly" I did. Sorry folks.

Click to expand...

It happens occasionally..
I usually notice 5 mins after.. so I can delete all the duplicated stuff.

Sometimes replacing with an afterthought.. or a useful web link.

There IS an option of contacting a moderator.. but I dont often go down that route..

Did have a reasonable 'faux pas' where a mod messaged me that I had quoted an entire thread.. which they had rightly deleted

Charlie