It is an ex-parrot, it has ceased to be

[Myros]

or more accurately, I have before me a former spark plug of the variety Bosch, FR8DC+ or, +6 as they are now known. Purchased on 8/03/06 by me, fitted on 11/03/06, by me ( one of the few things I can still do on a modern car). Removed from our C280 on Friday,by my mechie, after fitting the new coil packs and finding the car still had a woodpecker fitted.
The entire, and I mean entire, central body ( upper and lower insulator, nose and all) is free to rotate and wiggle about within the threaded outer electrode sleeve. The base of the upper insulator has an annular brown scorch mark where it meets, or used to meet the outer sleeve, obviously where escaping burning gases from the cylinder have scorched it. This free rattling movement we believe was the cause of the tappety-like noise that had me running to my mechie in the first place.
It wasn't like that when I put it in, and in nearly 30 years of plug-changing by the hundred, I've never seen anything like it. More to the point, neither has my mechie and his plug-changing tally must be in hundreds of thousands by now.
I'd like some none too carry-on type advice as to what to do with it please. I can't find an e-mail or phone number for Bosch UK, and I can't see the point of haranguing the poor sap at the motor factors who sold it to me, as they didn't make it faulty either. The problem has to be one of faulty manufacture, which means Bosch ought to be footing some of the bill for my recent automotive troubles.

Any clues as to how to get hold of them without resorting to snail mail would be appreciated, as would any other hints and tips.

 

[Blobcat]

It's asleep

Pls try the below,
Robert Bosch Ltd
Ph 01895 838 371
Fax 01895 838 333
email info@boschmotorsandcontrols.co.uk

 

[big x]

Ouch !, just bought 10 of these and fitted 6 to my E320.Mind you at just over a quid each at GSF it's not the end of the World as long as bits don't break off into the engine

 

[panason1c]

"Any clues as to how to get hold of them without resorting to snail mail would be appreciated, as would any other hints and tips."

You will probably have to send the plug off to bosch to be inspected/investigated so it would be an idea to take video evidence of it before you send it to them.

 

[Myros]

thanks fellas

an email has been sent. results, if any, will be made known. Of course, I'm now driving along listening for a repetition of the woodpecker in the engine.

 

[Myros]

and I phoned them as well, how old-fashioned of me

they were charming. I'm to send it off to them with a narrative and they'll see what they can do. I'll keep you informed, but I think the least I'm looking for is a fresh set of plugs, and the cost of a coil pack and the labour cost of diagnosing the fault and rectifying it.

 

[Myros]

Below are the findings of Bosch.

As though I would ever over-torque a plug. I haven't managed to do so yet in 28 years of motoring and car maintenance. Any ideas on how to test a torque wrench? In the meantime, NGK get my business.



Your Ref:

Our Ref:

Product Details

Part No: FR8DC+

Date code: 591

Factory code 060


Customer Complaint Faulty Spark plug







Bosch Findings On examination of the spark plug we found that the ceramic was loosing in the housing.
This was due to he inner seal being broken, we could also see exhaust gas marks on the ceramic.
The seal washer was measured and was found to be incorrectly deformed, the washer measured 1.13 to 1.20
this would indicate that the plug was over tightened. Based on the measurement of the washer the plugs where
torque at approx 23(Mn)
The seal washer was at the tolerance limit. At 20(Nm) the sealing washer should measure 1.33 + or - 3







Conclusion Spark plug has been over torque, no material or manufacturing defect was found

Spark plug will be returned under separate cover

 

[Blobcat]

Unsurprising really as they are unlikely to admit liability in the blame/claim driven world we now live in.
If you see a snap on van stop one, they have some very nice torque wrench testers. However the cheaper option is to test yours against a good one.

 

[Myros]

I wouldn't mind too much too much

but I've only been using the troque wrench ( a very classy and expensive one, xmas present from my missus) for a couple of years, before that, I used the half a turn beyond hand tight method, and never had a hiccup. That in itself is way over-torqued according to Bosch's website advice.
Rage against the machine is all that I can do. Time for a change of avatar I think.

 

[kth286]

All

Would someone like to explain to me how an over torqued plug can cause the insulator to work loose ????????????

Torqueing the metal threaded part of the plug does not cause anything to touch the ceramic part, so why should it matter ?????????

If no one has the answer, I would be inclined to ask Bosch again how it would affect the insulator coming loose.

Regards

 

[tom7035]

All

Would someone like to explain to me how an over torqued plug can cause the insulator to work loose ????????????

Torqueing the metal threaded part of the plug does not cause anything to touch the ceramic part, so why should it matter ?????????

If no one has the answer, I would be inclined to ask Bosch again how it would affect the insulator coming loose.

Regards

I think they'd be inclined to say the socket must have tilted due to the excessive torqueing-up. Surprised not even a replacement plug as a goodwill gesture!

 

[Uncle Benz]

Interesting..... In my Autodata book it states tightening torque for spark plugs at 25Nm for C280. Might check out who is correct.....

 

[panason1c]

http://www.ngk.de/Tightening_torques_for_spark_p.652.0.html


Tightening torques for spark plugs



When forces act through a lever on a fulcrum one speaks of torque.



This also applies to spark plug installation. Here, however, it is called a tightening torque. This describes how tight a screw is fastened.



In this conjunction a tightening torque is selected which will ensure that the connection will not become loose under any operating conditions.



It is important, therefore, to pay attention to the tightening torques and installation instructions when exchanging the spark plugs. These are given in detail in the main NGK catalogue. It is known from experience that though rarely much of the occurring temperature and vibration damage is caused by incorrect tightening torque, i.e. incorrect installation. Modern engines in particular react very sensitively in this respect.



When the tightening torque is too low, there is a danger of compression loss, loosening of the center electrode, and temperature damage due to reduced heat dissipation. It can also happen that the spark plug works itself loose. When tightening torque is too high, the cylinder head may become damaged. In addition, too high forces acting on the spark plug can cause damage to the thread.



The tightening torque can also be determined later by measuring the height (thickness) of the sealing ring. A spark plug has been installed with a non-compressed sealing ring with too low a torque. Vice versa has a spark plug with a sealing ring too strongly squeezed been installed with too high a tightening torque.






Summarising, three important points can be given as follows:
For correct spark plug installation it is necessary to adhere strictly to the tightening torque and the installation instructions.
Tightening torque can also be determined at a later time.
Modern engines react particularly sensitively to incorrect installation.





Tightening torques for spark plugs with flat seat (with seal):
18 mm 14 mm 12 mm 10 mm
Cast iron head 35-45 Nm 25-35 Nm 15-25 Nm 10-15 Nm
Aluminium head 35-40 Nm

25-30 Nm 15-20 Nm 10-12 Nm

 

[Myros]

thanks for all the input gang

I still have the original packing, and I'm absolutely sure I set the torque wrench to what the packet said. I've never ever had any trouble with spark plugs, even in a VW Beetle, which were a pig to fit compared to my lovely s6 M104. I just don't accept I have caused this problem.
Even though I only asked Bosch for 85 quid as a reasonable contribution to the over 200 quid I spent fixing this issue, I'm not going to let it lie. Even if all I do is waste 85 quid's worth of one of their executive's time, then honour will have been served.
Leav it with me for an update chaps.

 

[Glenn Smith]

All

Would someone like to explain to me how an over torqued plug can cause the insulator to work loose ????????????

Torqueing the metal threaded part of the plug does not cause anything to touch the ceramic part, so why should it matter ?????????

If no one has the answer, I would be inclined to ask Bosch again how it would affect the insulator coming loose.

Regards

This is much the same as asking why a mechanical service can effect bodywork warranty!! basically it can't, but it gets them out of paying warranty or replacing a plug. I'm guessing here but i think bosch will look at a returned plug, measure the washer, if in tolerance they replace, if not they don't regardless of fault, easy?

 

[panason1c]

All

Would someone like to explain to me how an over torqued plug can cause the insulator to work loose ????????????

Torqueing the metal threaded part of the plug does not cause anything to touch the ceramic part, so why should it matter ?????????

If no one has the answer, I would be inclined to ask Bosch again how it would affect the insulator coming loose.

Regards

The ceramic insulater is bonded(?) to the body of the plug, therefore, It is feasable, i suppose, that if the plug is over-tightened then it would be subjected to similar forces that are applied to a stretch bolt and cause the body to distort enough to result in the breaking of the 'bond' between the plug body and the ceramic insulation..............well, that's my theory anyway!

 

[Blobcat]

This is much the same as asking why a mechanical service can effect bodywork warranty!!

The answer to that is whilst your car is getting its service they check the bodywork. If there are stone chips that require touching up or anything else you will get an advisory. If you chose not to follow their advice then you may find trouble with the corrosion warranty.

 

[jberks]

The answer to that is whilst your car is getting its service they check the bodywork. If there are stone chips that require touching up or anything else you will get an advisory. If you chose not to follow their advice then you may find trouble with the corrosion warranty.

Sorry Blobcat, but I take issue there.
Perhaps they are supposed to do an inspection, but they never did in my case. I spotted the first rust just after a service and whilst I had other outbreaks, not once did they mention them to me. I even asked at one service for them to do a corrosion check and they put on the job sheet which I take to mean that it isn't there on the standard one.
I'll stick to my belief that it's a goodwill warranty primarily used to tie us to the dealer network - just like Mobilio.

 

[Blobcat]

Sorry Blobcat, but I take issue there.
Perhaps they are supposed to do an inspection, but they never did in my case. I spotted the first rust just after a service and whilst I had other outbreaks, not once did they mention them to me. I even asked at one service for them to do a corrosion check and they put on the job sheet which I take to mean that it isn't there on the standard one.
I'll stick to my belief that it's a goodwill warranty primarily used to tie us to the dealer network - just like Mobilio.

From my service book page 65;
'Every 2 years - 0090 Chassis and load-bearing chassis components: check for corrosion damage. 9850 Check bodywork for damaged paintwork' Those are the bits that keeps up the 30yr corrosion warranty.

 

[Myros]

anyway, back to the plot. Reply from Bosch.

Hello ,

Hopefully I can explain who the plug ceramic came loose.

If a spark plug is over tightened the body of the plug expands not by much but enough to break the internal seals. There are 2 internal seals one at the top and one at the bottom. These seal holds the ceramic part of the plug to the main body and also prevent exhaust gases escaping through the plug.

As you can appreciate the tolerance gap is quite tight and over tighting is quite easy. In 90% of cases where the plug has been over tightened there is not a problem and worst case the ceramic becomes loose. In our experience if the ceramic is loose this is the only damage and replacing the plug normally fixes the problem.

Based on the thickness of the sealing washer it would appear that the plug has been over tightened by 2NM as to the correct torque for your Mercedes you would need to speak to them, but in most cases 20nm is fairly standard.

I hope that this answers your questions.

For today I am out of the office for 3 weeks so if you need any additional information I will reply on my return

Best regards
Steve

Steve Howells
Support Manager
Robert Bosch
Automotive Division




Steve,



Thinking on this overnight, I have decided I will let this lie if you can answer the following questions and prove to me that it was any negligence or ham-fistedness of mine which caused this problem, rather than as I assert, a faulty spark plug manufactured by your company.



What is the correct tightening torque for one of these spark plugs as fitted to a Mercedes M104 2.8 litre 6 cylinder engine? Do bear in mind that I still have the original packing which states quite clearly to what torque the plug should be tightened.



How does allegedly over-torquing a spark plug detach the central insulator and electrode from the threaded outer ring?





Regards



Myros