kastnna

Just heard back from the autoshop...

No cross-threading, but the tech said that it appeared that the plugs were overtightened to the point that the plugs were compromised. Engine heat and combustion did the rest.

They didn't see any visibly apparent damage to the engine and are in the process of removing the plug threads with an easy out. Then they are going to drop a magnet into the engine to get any metallic pieces. I don't know what they'll do about any of the ceramics.

If there are pieces of plug resting at the head of the cats, will they need to go in and remove that material? Would it be bad if the engine was started before doing so? I don't want to destroy anything else. Will I be able to hear the material in the exhaust.

By the way - yes - two of my plugs looked pretty much identical to the ones in the picture. I really wish I had taken a picture of the plug boot on cylinder 5. It literally looked like someone shoved a bottle rocket into the boot and set it off. As pissed/terrified as I was, the sight actually made me chuckle a bit.

kastnna

thanks for thinking out loud. I don't like to jump to too many conclusions, so I'm all for laying out all the possibilities.

By the way, I ONLY run 93 octane and stick to Techron and then V-power when I have the choice. Jonathan Hodgman at BlueRidge Mercedes has my base map set to the most aggressive timing. It's been that way for a while.

mleskovar

I agree with Glyn's advice of using a boroscope to check out each cylinder for damage and pieces left behind. You can check for pieces in the cats by hitting the cats with your hand and listening for rattles. I don't think they would do any damage though....unless they were big enough to block holes and there are a bunch of them.

mleskovar

My theory.....over tightening the plugs compromised/cracked/stretched the plug material. His engine has one plug per cylinder.

kastnna

Actually it now has no plugs per cylinder

I guess I better make sure they put the borescope in the cylinders. That hasn't been mentioned thus far which makes me nervous that they don't intend to do it.

I have no doubt that if they fired up the engine while it was full of ceramic, I'd still be the one writing the check at the end of the day.

Glyn M Ruck

Small stuff will likely blow out of the exhaust but please insist on a boroscope test. You don't want to do any unecessary damage. All you need is one piece of hard material in the wrong place. Benz alusil bores are as tough as hell but I would hate to see you score one or worse - bend a valve. There is not much space in a 4 valve per cylinder head.

Glyn M Ruck

No - the metal part of the Audi plug is not compromised. It's a ceramic failure at high pressure

Glyn M Ruck

Ed - yes, a helicoil is more than strong enough. VW's with ultra short reach plugs with very little thread have been surviving on them for years.

Cross threading a plug this long is almost impossible. It would not go in very far & would be very obvious.

MBtech1098

When you torqued it, were you reading NM or ft lbs? Some torque wrenches are labeled with both. 20ft lbs is 27NM

Glyn M Ruck

Right - well it seems that this is clearly a case of over tightening of the plugs & to a large degree.

To someone that does not do this every day you do not realise the leverage you have with a long torque wrench.

I know you are probably feeling relieved that this has the appearance of a happy ending but if you are satisfied that you set the wrench correctly I would be taking it to be checked and if found to be out of calibration then ask the vendor for a contribution to the bill.

We buy torque wrenches so that we don't over tighten things!

I would also like to know the history of that short NGK plug in the engine but I guess we will never know.

MBtech1098

In the US, the NGK is the factory spark plug in the 272.

Glyn M Ruck

Yes - but at 26.5mm (1.04") Reach. The plug in the pic is wrong & will not protrude correctly effectively making it the wrong heat range & causing some flame shielding.

MBtech1098

What is the number on the NGK plug?? (I did not notice it posted) Remember pictures can be quite deceiving...and what's the VIN. You can PM it to me and I can tell ya what is suppose to be in there as per EPC.

kastnna

yeah, I'm a little upset about the torque wrench and/or me being the culprit. I do intend to make sure the torque wrench works properly. Otherwise, I might as well throw it in the trash b/c I can't exactly trust it at this point.

By the way, I'm surprised it took this long for someone to ask, but, "yes," I did make sure (repeatedly) that I was using newton-meters and not foot-pounds. The wrench does have both.

As for the NKG plug, I don't know how they came to live in my engine. I bought it used and they were already in there. The car only had 28k miles when I bought it, so I doubt they were replacements. The plug is numbered PLKR6A. For better or worse, it has a MB star printed on it by NKG.

mleskovar

Ah....I was reading the picture wrong.

e1000

The correct NGK plug is the PLKR7A!!!!!!!!!!!!!!!! This matches with the Bosch YR7MPP33 and Denso SC20HR11. So the plugs you had in previously were incorrect

Not only that, but check out this thread from Benzworld.

http://www.benzworld.org/forums/w211...e-strange.html

** EDIT ** I'm going to my self storage unit and pulling the old plugs I saved when I changed my plugs out many moons ago. I'll report back later....... and the plot thickens.

kastnna

yeah, I was just now discovering that as well. NGK website has the 7A, not the 6A listed. That's wierd. I've been running those plugs for 2 1/2 years and I doubt they were put in the day before I bought the car.

I can't seem to find specs for either of those NGK plugs. Is the 6A possibly just a hotter version of the 7A?

e1000

Ok, so I did one better. The NGK plugs that came out of my car were also PLKR6A's!. See HERE.

After a little digging, I can't seem to find the difference between the PLKR6A and PLKR7A. They have the same length, same gap. Also, I do distinctly remember comparing the Bosch YR7MPP33 plug to the OE plug in my car (PLKR6A) and they were physically identical. I am also positive they were YR7MPP33 because I just looked up my order.

e1000

Yup you were right the only difference between the PLKR6A and PLKR7A is temperature. The PLKR7A is a slightly cooler plug. They should be physically idential.

Militant-Grunt

What I did with mine is, I ran the motor with the plug / coil pack removed on that particular cylinder, whatever was inside got blown out through the spark plug hole. Though if you already put a plug back in, theres a good chance that any debris mightve slightly bent one of your valves. I suggest you do a compression / leak down test.

MBtech1098

Kastnna,

I just had parts pull a brand new plug and checked it...previous posts are correct PLKR7A is the correct plug. Also not that it's a big deal, but the origional number you gave me supersedes in paragon to a 004-159-49-03.

Glyn M Ruck

The NGK PLKR6A was the correct plug for the M272 engines from 2.5 to 3.5l. at the time of it's launch in the German media - interesting! It is also 26.5 reach - same as the Bosch. So that picture is misleading.

So, however, are pictures of these plugs shown on the internet which show more threads on the Bosch than the NGK. This is impossible for a 26.5mm reach as the thread pitch has to be the same by definition.

Song

man,.. I was going to change the plugs by myself. now too scare to do it..

kastnna

Nah... don't let me discourage you. Just make sure you use a good quality torque wrench and/or you know how to properly use it.

Honestly, I have changed my spark plugs for years in my other cars (this is the first MB for me) without even using a torque wrench. I would just hand tighten the plugs and then go another 1/4 to 1/2 turn past that with a regular socket wrench. Never had the first bit of trouble.

C230 Sport Coup

My car came with NGK's, and they were replaced under warranty, also NGK's.
Quite expensive, and I believe they are like their performance racing division plugs that MB uses.
I now run the iridium 2 steps cooler for the OD pulley.

I don't like Bosch. I had a set that shorted out after less than 1000 miles, shorted from the metal to the ceramic, brought the car to it's knees.