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Burnt Exhaust Valves


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j.hilmar.christens

Here we go again! Lost whole lot when tried to make my pics smaller, so to cut to chase removed cylinder head, as you'll see burnt valves, what caused it? Common fault with 1.2 Cylinder MK7 engines? Been told supermarket fuel, servo had gone, result of timing chain stretch? Chain was changed and think was missfiring before... The final diagnosis was leak test.... Didn't seem to find prob when did compression test... Note bolts can seize and thread will either need re tapped or thread insert with special tools needed... Videos on you tube... I had 1.4 polo 2001 plate, never had this problem.. This polo done over 100k, been told frequent oil changes important too as its timing chain.. Every 5k? I'm curious others out there what experience you've had with this MK7... Mechanic still rebuilding, took most of day to break... Any idea how long it should take to break and rebuild? Was quoted £300 for labour from another mechanic... Recon was £340.... 

 

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Edited by j.hilmar.christens
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Supermarket fuel will not be the problem.  Approximately half of all petrol sold in the UK comes out of pumps at supermarkets, so this problem would be far more common if that were the cause. It'

No way of knowing when the damage happened, or started to happen really. Just make sure it gets regular oil/filter changes from now on.  I personally do the missus's Fabia (12-valve 1.2) twice a year,

I had oil change last year... Not doing that many miles as you know... Filter too and sparks... Thanks for all your advise Pete! 

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Supermarket fuel will not be the problem.  Approximately half of all petrol sold in the UK comes out of pumps at supermarkets, so this problem would be far more common if that were the cause.

It's not clear to me what you mean by 'servo had gone'? There's a common fault with failure of the vacuum hose to the brake servo, but that's not a fault with the servo itself.

 

How often was the oil and filter getting changed on this car? Which oil was being used?

Have you had any fault lights on?

Does the radiator fan work? Does the temperature gauge ever go above 90°C? Does it use/lose any coolant?

 

Make sure your garage checks the degree of wear to the exhaust valve guides. These are often mentioned as being the precursor to this failure,  too much waggle-room and the exhaust valves don't seal properly, leading to overheating due to poor conduction path into the head metalwork. What wears the valve guides excessively is another (or possibly the main) question, of course.

Edited by Pete1
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j.hilmar.christens

Pete, I got the car Sept 2018. Do have all paperwork and did go thru it, don't seem like was serviced well...it was servo pipe that had to get replaced.. That was what mechanic thinks caused overheat... I did question my radiator leak... The temp was half way up gauge, so not sure what that was, not got car back yet... Recon was very good, like brand new, needed new guides.. I have been servicing well since got car... Its VW mechanic. Will really annoy me all that you suggested should have been signs I wonder before or after I bought the car... Thanks for quick reply Pete.

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j.hilmar.christens
2 hours ago, Pete1 said:

Supermarket fuel will not be the problem.  Approximately half of all petrol sold in the UK comes out of pumps at supermarkets, so this problem would be far more common if that were the cause.

It's not clear to me what you mean by 'servo had gone'? There's a common fault with failure of the vacuum hose to the brake servo, but that's not a fault with the servo itself.

 

How often was the oil and filter getting changed on this car? Which oil was being used?

Have you had any fault lights on?

Does the radiator fan work? Does the temperature gauge ever go above 90°C? Does it use/lose any coolant?

 

Make sure your garage checks the degree of wear to the exhaust valve guides. These are often mentioned as being the precursor to this failure,  too much waggle-room and the exhaust valves don't seal properly, leading to overheating due to poor conduction path into the head metalwork. What wears the valve guides excessively is another (or possibly the main) question, of course.

 

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j.hilmar.christens

I'm now thinking this could all have happened after I got car? How long would it take for valves to burn out?

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No way of knowing when the damage happened, or started to happen really. Just make sure it gets regular oil/filter changes from now on.  I personally do the missus's Fabia (12-valve 1.2) twice a year, roughly every 6k miles. It's on 173k, which seems good going. I think it was reasonably well looked after prior to our ownership, for its first 100k, and did reasonable-length journeys judging by it having covered that in the first 7 years. What's your usage pattern? Short journeys are bad for oil life.

 

Temperature gauge in the middle sounds OK.

 

Thermoswitch on the radiator (just above bottom hose connection) is a common source of coolant leakage, just nip it up a bit tighter and it stops.

 

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j.hilmar.christens

I looked at paperwork and previous owner only serviced every two years, around 20k miles, oil change and filters...it's catching these signs early that we all need to learn and I'd hope my mechanic would know that too... Good money for him on the side... And the recon guys... 🙄

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j.hilmar.christens
16 minutes ago, Pete1 said:

No way of knowing when the damage happened, or started to happen really. Just make sure it gets regular oil/filter changes from now on.  I personally do the missus's Fabia (12-valve 1.2) twice a year, roughly every 6k miles. It's on 173k, which seems good going. I think it was reasonably well looked after prior to our ownership, for its first 100k, and did reasonable-length journeys judging by it having covered that in the first 7 years. What's your usage pattern? Short journeys are bad for oil life.

 

Temperature gauge in the middle sounds OK.

 

Thermoswitch on the radiator (just above bottom hose connection) is a common source of coolant leakage, just nip it up a bit tighter and it stops.

 

I mainly do short journeys, around 15 miles... To and from work... 

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17 minutes ago, j.hilmar.christens said:

previous owner only serviced every two years, around 20k miles, oil change and filters

Ok, that'll be the main issue.  If it were mine and I wanted significant future life out of it, I'd be taking off the sump to remove sludge/solids and making sure the oil pick-up is clear as a whistle; and check the breather system isn't clogged up.  Not jobs you want to add to your current bills though, I suspect.

 

15 miles each way is fine, plenty of time at full temperature. :smile:

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j.hilmar.christens

I had oil change last year... Not doing that many miles as you know... Filter too and sparks... Thanks for all your advise Pete! 

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j.hilmar.christens
3 hours ago, Pete1 said:

Supermarket fuel will not be the problem.  Approximately half of all petrol sold in the UK comes out of pumps at supermarkets, so this problem would be far more common if that were the cause.

It's not clear to me what you mean by 'servo had gone'? There's a common fault with failure of the vacuum hose to the brake servo, but that's not a fault with the servo itself.

 

How often was the oil and filter getting changed on this car? Which oil was being used?

Have you had any fault lights on?

Does the radiator fan work? Does the temperature gauge ever go above 90°C? Does it use/lose any coolant?

 

Make sure your garage checks the degree of wear to the exhaust valve guides. These are often mentioned as being the precursor to this failure,  too much waggle-room and the exhaust valves don't seal properly, leading to overheating due to poor conduction path into the head metalwork. What wears the valve guides excessively is another (or possibly the main) question, of course.

Forgot to say, initially did think engine not running well at idle.. First yellow engine light came on and that was cam shaft, that's when chain was changed and had stretched... £290 for that! Then light came on now and again and that we did diagnosis, missfire cylinder one that's worst damaged valve as you can see... I did have problems starting the car now and again... It was mainly low revs there was problem... But higher revs okish... Not as much power... This has been going on for months and should have niped in bud.. We then had lockdown and mechanic was not getting on the case as his work at VW came first... Worst was when light came on and was flashing like mad and total loss of power and engine cut out... 

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6 minutes ago, j.hilmar.christens said:

Worst was when light came on and was flashing like mad and total loss of power and engine cut out... 

Been there got the t-shirt. In our case it was a failed ignition pencil coil, but either way, if the engine ECU detects sufficient misfires on any given cylinder, it completely cuts fuelling to that one.  On the three-pots this is quite a severe reduction in output and engine balance.

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j.hilmar.christens
16 minutes ago, Pete1 said:

Been there got the t-shirt. In our case it was a failed ignition pencil coil, but either way, if the engine ECU detects sufficient misfires on any given cylinder, it completely cuts fuelling to that one.  On the three-pots this is quite a severe reduction in output and engine balance.

We checked everything, coils, sparks, injector and last resort as I said was leak test, don't know why did not get picked up when compression test was done, I don't get others have said check spark spacing? I'd hope when you get new sparks they would be correct? 

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As long as the little cardboard tubes have been in position to protect the plugs from end-impact between factory and your engine, I tend to agree.

 

What were the compression figures?

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j.hilmar.christens

No idea about sparks tubes.... Compression figures too... Got a video of leak test... 

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j.hilmar.christens
2 hours ago, Pete1 said:

As long as the little cardboard tubes have been in position to protect the plugs from end-impact between factory and your engine, I tend to agree.

 

What were the compression figures?

Here's leak test... Before and after, need to zoom in... Obviously you can see its only in yellow bit then drops to red... They put a rubber glove ond of exhaust... How would they know exhaust valve was closed? 

Screenshot_20200607-144257.png

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I know nothing about leakage testing, was just wondering if the compression figures from the actual compression test that was done were near the 'wear limit' figure which is extremely low in my opinion. this is from the workshop manual:

Compression pressures:

New: 10…15 bar.

Wear limit: 7 bar.

Maximum permissible difference between all cylinders: 3 bar

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j.hilmar.christens

I'll ask mechanic... I just know all three cylinders were same, think was warm engine... 

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j.hilmar.christens
On 06/06/2020 at 19:18, j.hilmar.christens said:

Here we go again! Lost whole lot when tried to make my pics smaller, so to cut to chase removed cylinder head, as you'll see burnt valves, what caused it? Common fault with 1.2 Cylinder MK7 engines? Been told supermarket fuel, servo had gone, result of timing chain stretch? Chain was changed and think was missfiring before... The final diagnosis was leak test.... Didn't seem to find prob when did compression test... Note bolts can seize and thread will either need re tapped or thread insert with special tools needed... Videos on you tube... I had 1.4 polo 2001 plate, never had this problem.. This polo done over 100k, been told frequent oil changes important too as its timing chain.. Every 5k? I'm curious others out there what experience you've had with this MK7... Mechanic still rebuilding, took most of day to break... Any idea how long it should take to break and rebuild? Was quoted £300 for labour from another mechanic... Recon was £340.... 

 

DSC_0946.JPG

DSC_0945.JPG

Thought I'd give update, Pete has been great as you'll see with his excellent advise, but need to pick his brain again... 

 

Got the car back... £400 labour bill! This was break down and rebuild... Mechanic also retapped the engine head for the cylinder head bolts... Few issues still, now missfire moved from cylinder 1 to 3...going to check injectors... Cam shaft sensor went on again... We think faulty... Its new sensor... Cam timing was checked and all OK... The cat full of stuff, did not know can drill to clear it out... So that's about it.. The total damage for recon and labour £740!

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14 hours ago, j.hilmar.christens said:

but need to pick his brain again..

Not sure quite what you're asking?

Misfires that aren't casued by compression issues on these engines are most often due to coilpack failures, but injector problems may also have the same effect. Best diagnostic test is to move (cyl 3) coilpack to a different cylinder, move cyl 3 injector to the other different cylinder, then run for a while and see which cylinder now misfires.

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j.hilmar.christens

Yes, that's what we'll do... Thanks again.... 

Edited by j.hilmar.christens
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j.hilmar.christens
11 hours ago, Pete1 said:

Not sure quite what you're asking?

Misfires that aren't casued by compression issues on these engines are most often due to coilpack failures, but injector problems may also have the same effect. Best diagnostic test is to move (cyl 3) coilpack to a different cylinder, move cyl 3 injector to the other different cylinder, then run for a while and see which cylinder now misfires.

I'm still puzzled, originally it was cylinder 1 missfire... Now after rebuild gone to cylinder 3...

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j.hilmar.christens
On 11/06/2020 at 10:03, Pete1 said:

Not sure quite what you're asking?

Misfires that aren't casued by compression issues on these engines are most often due to coilpack failures, but injector problems may also have the same effect. Best diagnostic test is to move (cyl 3) coilpack to a different cylinder, move cyl 3 injector to the other different cylinder, then run for a while and see which cylinder now misfires.

Pete, going to change injector seals too... Turns out have to get direct from VW... What a difference with cylinder head recon... Still feel something tho due to cylinder 3 misfire... Still puzzles me tho never had issue with 3, it was 1 before break down and 1 was worst damaged valves...

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caretakerplus

It is important to remember that the only time that an exhaust valve is cooled, is when it is clamped to its seat in the first three parts of the cycle.

The problem is that, if the actual contact area of the valve and seat is too narrow, very little cooling takes place BUT if the contact area is too wide, then there clamping load from the valve spring is shared out over that wide area, resulting in low contact pressure, in turn resulting in poor seating.

I would suggest that you ask your local machine shop to carry out a 'three angle grind' on those exhaust valve seats, the final angle determining the the contact area.

 

Other causes of this kind of problem include: Wrong spark plugs; Weak mixture (a richer mixture has a cooling effect); Wrong valve timing.

Frequent oil and filter changes can (amongst other things) improve the action of the hydraulic tappets - but only if the recommended grade of oil is used.

 

The argument about supermarket petrol will go on for ever, personally, I always use Shell V Power. - I know of people who have tried that and claimed that they couldn't tell any difference - well, they wouldn't would they - First of all, the V Power will be diluted by whatever else is in the tank, secondly V Power has a cleaning effect in the combustion chambers, but for this to happen, you may need to use it for a while.

What I have found with V Power, is that I obtain better fuel consumption, but as always, this depends on how you drive. The engine is definitely smoother running though.

 

Regards

 

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