e1000

Yup, just looked up my order and I bought YR7MPP33's from AutohausAZ. Wonder if there are similar plugs with longer threads that he got.

Glyn M Ruck

Not available in different reach according to the Bosch plug finder.

Bosch OE Type Platinum Spark Plug YR7MPP33

Double Platinum, 12mm Thread Size, 26.5mm (1.04") Reach, 5/8" (16mm) Hex Size, Gasket Seat, Interference Suppression Resistor, Platinum Tipped Fine Wire Center Electrode, Mono Nickel-Yttrium Ground Electrode with Laser-Alloyed Platinum Inlay, Solid Terminal Nut, .032" (0.8mm) Gap, Heat Range 7

Bosch uses a platinum center electrode that's heat fused into the extended ceramic insulator. Bosch platinum series spark plugs reach self cleaning temperature faster for quicker starts, smoother acceleration and increased fuel efficiency. The tapered, v-profile nickel ground electrode provides improved starting in cold weather and increased fuel ignitibility.

mleskovar

Even though it looks like the reach of the new plugs is longer I don't think that's the problem. That tip would be gone if the piston smacked the electrode hard enough to destroy it and part the plug at the threads. If it was overtightened enough to part the body of the plug at the threads you would think they would have pulled the threads out of the head first. But I think that's what happened....overtightened, and as the head expanded to operating temp they split the plugs at the weakest point. Or, there was a bad batch of plugs (doubtful). Email Bosch, show them the pictures, and ask their opinion. I've never seen/heard this happen.

kastnna

thanks for the input, guys.

Like I said, this was the only set of plugs on the autohaus website. And the plugs I removed were definitely a little bit shorter, but I didn't put them in. I assumed they were originals but I'm not sure since I bought the car used. They are NKG, but they also have the MB star imprinted on them. It appears the replacement plugs are the right ones to be using, so I'm not sure where I stand.

Maybe I did overtighten to the point that the thread cylinder broke free from the rest of the plug at operating temp. But how hard can it possibly be to push a torque wrench until it "clicks"?

P.S. - I doubt it was a bad set of plugs. At first, 1 of the 6 plugs autohaus sent me was the wrong one. I had to have the order corrected which took two weeks. So unless they have low inventory turnover, at least one plug should have been from a different batch.

e1000

what did you torque the plugs down to? What was the torque wrench set at?

ontmiss

As I can see from picture, exploded one is much longer

Glyn M Ruck

OP claims 20 Nm which is correct. So it's either a screwed up torque wrench or the pull angle under the hood interfered.

Glyn M Ruck

Mark - I tend to agree with you but it would be the earth hoop that would take the initial clout if someting touched. For all the plugs to show some tip damage I do suspect a slight touch. I would like to see a pic of the plug that came out relatively intact.

The OP seems to have used the correct plug at the correct torque. He needs to go back & think about this & his torque wrench setting.

Plugs are incredibly strong things. In all my years of racing etc. I have never seen a failure like this. I have seen a piston touch a plug at 19,000RPM on a racing two-stroke running very tight squish bands due to roller crank flex & rod stretch - but even that just closed the gap - no further damage.

I would like us to understand this so that it does not happen again & we can warn members.

I would get Bosch involved for comment

I would like to know if Benz have some heads out there on M272 engines that need that shorter NGK plug - it is, after all branded. The M271 engine takes a 19mm reach plug which might explain things.

kastnna

Could definitely be the torque wrench (it was new), or user error. I'm not ruling out either. The wrench was set to 20 Nm, as was called for on the bosch packaging.

And although it is possible, I REALLY don't think that the plugs were over-torqued specifically due to having the wrench at a non-90-degree angle. I was actually quite impressed with how much room I had. For each plug, I fitted a plug socket and extension rod onto the plug so that the end of the extension only protruded about 2" out of the plug chamber. It was very easy to then fit the torque wrench onto the extension and have plenty of room to manuever the wrench.

But then again, in the past, without a torque wrench, I would hand tighten plugs and then turn them an extra 1/4 - 1/2 turn with a standard socket wrench. Never had any trouble. This torque wrench probably gave me 1 - 1 1/2 full turns after hand tightening before clicking. I remember thinking that I must have been undertightening my plugs my whole life.

The one plug that remained intact is at the mechanics with my car. I'll try to post pics later on. If memory serves, it looked exactly like a normal plug except you could hold the ceramic coating and freely spin the metal body of the plug. I don't specifically recall the earth hoop being smashed into the electrode, but I could be wrong. When I first removed it, I thought it was undamaged.

I'm contacting Bosch today.

Glyn M Ruck

Pleased you are contacting Bosch.

And - yes - the M272 is a lot easier with it's single plug per cylinder - The angle is comfortable compared with the older M112 V6's like mine with twin plugs per cylinder that can be a PITA with the rear plugs.

benzmodz

Take your torque wrench to the store and try it out against another torque wrench like a snap-on. What you may have is in fact a faulty torque wrench. The only way to find out is to see what readings it gives against another torque wrench set to 25Nm.

If your torque wrench clicks after the other wrench then your calibration is hopelessly out.

All you need is a deep nut to be able to put both on at the same time.Or weld up something ... or similar.


Generally speaking, 90% of mechanics use hand feel to insert a plug. The wind it backwards first till they feel the thread seat itself at the start point. Then they wind it forwards. Looks to me a combination of wrong plug and wrong force. It can also be a defect but what are the odds.

Glyn M Ruck

Snap on have TW calibration centers in SA

And it is the recommended OE plug

Warren & Brown make the finest Torque Wrenches

benzmodz

Indeed W&B are good. Is that what the OP used ?

pcy

I've just checked on both Autohaus and RMeuropean sites. BOTH of the sites list EXACTLY the same spark plug. Autohaus listed the same plug as "Bosch OES" while RMeuropean listed the same plug as "BOSCH Original Equipment".

The first picture below is Autohaus and the second picture is RMeuropean.

Glyn M Ruck

I have no idea what the OP used.

Militant-Grunt

Similar thing happened to me @ triple digit speed. I do have the correct plugs though, I think the plug might have cracked over time, the entire center park shot out into the coil pack, destroying my coil pack and the rest of the thread stayed inside. Luckily I had tools and a spare plug, hour later I got all the pieces out, removed the thread and was back on the road haha. This was a Bosch F5DP0R, an expensive boost specific / audi specific plug.

Glyn M Ruck

A very different failure mode but bad news nevertheless !

kastnna

At work at the moment, and don't remember which wrench I bought. I'm sure it wasn't the best. Cost me, like, $40 at Advance Auto Parts.

While the car is at the mechanic, anybody want to speculate on the likely damage and how much it's gonna cost me. $2,000...? $5k...? $10k...? Four of the plugs came out mostly intact except for the stuck threading, so hopefully no debris made it into the engine. But as for the two plugs that pretty much completely exploded, I'd be surprised if a little bit of the ceramic housing or the electrode didn't get into the engine. As I said in my OP, because of where I was at, I had to gingerly drive the car back home (about a mile).

johnand

As Glyn pointed out, pistons are damn strong, so I speculate the engine is ok, once all the debris is removed. Just hope the threads in the head for the spark plugs are ok. They can be repaired if not too bad.

kastnna

I'm actually least worried about the threads ("least" being a relative term). I think they would be ruined primarily if I cross-threaded the plugs, right? I just don't think I did that. Over-torqued, maybe. But not cross-threaded.

Like I said, one plug came out whole and it too was damaged, but showed no signs of cross-threading. So if cross-threading is the issue, what damaged that plug? And what are the chances that I cross-threaded every single plug when I was hand tightening only. The threads would have to have been made of play-doh for me to have so easily cross-threaded. I didn't involve a wrench/ratchet of any kind until the very end. It was all hands during the initial install.

johnand

The heads on your car are aluminum, so they can be damaged much easier than traditional cast iron, but you would still know that you were cross-threading them if you did screw them down by hand. The threads can be repaired several ways if need be.

mleskovar

Actually that looks like an identical failure to me Glyn. Broken right where the plug threads end with the threads left in the head. No? Maybe we are looking at plug material failure. I'm real curious now.

SeaCoupe

Damn this is a scary thread.

I think your damages will be less than you think. The broken bits got blown into your exhaust and likely at the entrace to your cat.

Once the plugs come out, the threads get examined and I'm sure that if needed a repair can be made to the threads. Glyn is a helicoil strong enough in this circumstance?

Sorry to go off topic, but when I was a kid, I thought I would do a tune up on our family lawn mower. I of course ruined the aluminum head, and distinctly remember how it feels. If I'm putting in a spark plug and I don't like how it feels I back it out.

I can understand questioning mechanicall skills. When I didn't know the M1111 had spark plug seals, I thought I might have cross threaded mine.

Ed

zerocover

Helicoil inserts are incredibly strong. Much stronger then the aluminum they will be sitting in. It would make for a solid repair.

I've used them in way higher stress applications then an automotive head.

DrgnflyZ28

Just throwing this out there...

If it was plug to piston contact, would it not have been evident upon startup and initial revving to 2500rpm not just WOT. How can an over-torqued spark plug increase the chances of it blowing out... let alone both? If the OP's method of installing a spark plug is sound, it's extremely coincidental that he missed both plugs on one cylinder. Just doesn't add up.
The condition of those plugs lead me to believe there was an extreme amount of pressure or heat, enough to dislodge the ceramic from the threading and fire both plugs out of their own housing. For being brand new, those plugs already show some serious signs of heat. I'm leaning towards a lean condition, maybe predetonation.

Just thinking out loud...