[wesmeister]

Just wondering if anyone here has ever experienced a super knock condition causing a spark plug to almost literally shatter and shut the gap?



2016 F31
26K miles
Lots of 89 octane fill-ups by previous owner
Super knock at about 4.5K rpm... with cylinder shut down immediately after (all cylinders, except 1) and totally repeatable every time

• Compression tested - 170 psi on all 4 cylinders
• Fuel pressure test - within specs
• ISTA diagnosis - STOCK All the firmware on the DME and EGS has has been updated and verified by BMW tech support
• Bore Scope - Small knick on piston, possible contact with spark plug?

Is it even possible for an N20 piston to reach the spark plug without hitting the valves first?
Could severe pre-ignition/detonation cause this kind of damage?
My thought right now is a "leaky" injector...

I have a full online diagnosis from my shop. If anyone helpful wants to see everything they have done, I can PM you the link.

[thejeremyman9]

By "totally repeatable every time" do you mean that you always get a big knock event at 4.5k RPM? And then when doing this one time, you got the damage shown here? Just trying to understand the sequence of events.

Also, were these plugs every changed? Asking because a common mistake is not using a Ujoint or flex socket and cracking the ceramic during install and torque.

Yes, knock can cause the gap to be pushed closed; it can even break off spark plug tips. Not sure about the damage to the ceramic though, that's why i asked the question above.

[IraHayes]

Has anyone confirmed that those are the correct spark plugs? I'd go to the NGK website and look up the spark plugs for your car and compare the item numbers. If they do match, are they legit? Numerous threads on car forums about bogus Chinese knock-offs being sold on Amazon, and even purchased at some of the big box auto parts stores. I would get a spark plug from a known good source like the dealership and compare it to those.

[BMWILUVU]

Why would super-knock shatter the ceramic? My guess is the plug was micro-cracked on install. I would also check or replace the coil on cylinder 3 and then move to injector tests.

[thejeremyman9]

Originally Posted by BMWILUVU

Why would super-knock shatter the ceramic? My guess is the plug was micro-cracked on install. I would also check or replace the coil on cylinder 3 and then move to injector tests.

Yeah, this is why i asked if then plugs were original, and if not, if he used a ujoint per the manual. The car only has 26k miles so its possible they were the original plugs. Lots of threads recently of people cracking the ceramic by using only a straight extension.

[wesmeister]

Plugs are new, less than 500 miles, OEM NGK SILZKBR8D8S. Purchased from FPC Euro about a month ago.

They were removed by my mechanic and inspected when I brought the car in, then reinstalled, after he verified their was no weird marking or burn on each one. Later, on one of the test drives after doing all the DME reprogramming, the car super knocked at the usual 5K-ish rpm's... and when they limped it back to the shop, what you see in that picture is what they found.

They can recreate the almost every time, by driving the car around for about 10 minutes to get the IATs up to full normal temps, and then accelerate to about 4.5K or 5K rpms. The car feels like it hits a wall, as typically all but one cylinder is shutdown by the DME.

Here is what the borescope saw after the spark plug was removed.



I'm just not convinced that the piston made actual physical contact with the piston. Seems to me that maybe scarring like that can happen with pre-ignition also?

[thejeremyman9]

So it's still not clear to me, were there any issues (including this "super knock") before you changed the plugs? Or did it all start after the plug change?

I still think, as others have suggested as well, that the plug was cracked during install (or removal and reinstallation). The damage shown in the picture could have then occurred as a result. There was another thread recently where someone broke the ceramic on their plug and got debris into the cylinders.

I don't see how the piston could have hit the spark plug... but that mark does not look like detonation/knock; that is usually small pitting, not a clear mark like that.

[BMWILUVU]

Originally Posted by wesmeister

Plugs are new, less than 500 miles, OEM NGK SILZKBR8D8S. Purchased from FPC Euro about a month ago.

They were removed by my mechanic and inspected when I brought the car in, then reinstalled, after he verified their was no weird marking or burn on each one. Later, on one of the test drives after doing all the DME reprogramming, the car super knocked at the usual 5K-ish rpm's... and when they limped it back to the shop, what you see in that picture is what they found.

They can recreate the almost every time, by driving the car around for about 10 minutes to get the IATs up to full normal temps, and then accelerate to about 4.5K or 5K rpms. The car feels like it hits a wall, as typically all but one cylinder is shutdown by the DME.

Here is what the borescope saw after the spark plug was removed.



I'm just not convinced that the piston made actual physical contact with the piston. Seems to me that maybe scarring like that can happen with pre-ignition also?

The picture is not clear but that may look like valve slap but if its flush in the middle, it may be the plug. Not good either way.

[Billfitz]

The piston can't contact the plug. It can't contact a valve either, the valve timing would have to be so far off that the engine wouldn't run.

[HighlandPete]

Originally Posted by wesmeister

Is it even possible for an N20 piston to reach the spark plug without hitting the valves first?
Could severe pre-ignition/detonation cause this kind of damage?

Not if it is the correct plug (length). Mechanically it can't touch, impossible to protrude into the head more than specification. If the ground electrode is still in position, it hasn't protruded more than spec'.

If the piston is coming up more than design, you do have issues, big problems.

Pre-ignition does cause more heat, but wouldn't expect enough heat to damage the plug ceramic. But you can't rule it out.

BTW, the plug doesn't look to have overheated from the picture posted.

[JimKden]

The ground strap on the damaged plug would have been deformed and/or marked if the piston touched it. Photo doesn't show clearly the no 3 plug in that area.

[wesmeister]

Originally Posted by JimKden

The ground strap on the damaged plug would have been deformed and/or marked if the piston touched it. Photo doesn't show clearly the no 3 plug in that area.

It is hard to see, but the electrode gap was closed on that plug just slightly.

Just got these borescope pics... not sure what to make of them yet.

[wesmeister]

And the leak-down test showed 30% loss in both cylinder 1 & 2

The compression test had me hopeful that there was no cylinder or piston related issues... but that hope is fading away.

Considering that the previous owner ran the car on 89 octane, I can only assume that they also didn't bother with oil changes. Or they used cheap oil not to BMW specs. My mechanic actually mentioned he was surprised how dark it was already, as the dealership that I bought it from would have changed it before selling it.



Not sure if I'm screwed or not... yet!

[n00bkiller944]

This seems weird. And those boroscope pics are pretty bad, normally you can get a much clearer imagine. Maybe go in and see for yourself on the live camera?

[BMWILUVU]

Originally Posted by wesmeister

And the leak-down test showed 30% loss in both cylinder 1 & 2

The compression test had me hopeful that there was no cylinder or piston related issues... but that hope is fading away.

Considering that the previous owner ran the car on 89 octane, I can only assume that they also didn't bother with oil changes. Or they used cheap oil not to BMW specs. My mechanic actually mentioned he was surprised how dark it was already, as the dealership that I bought it from would have changed it before selling it.



Not sure if I'm screwed or not... yet!

Not great. My bet is leaking from the valves or rings maybe from impact of high-RPM pre-detonation timing being off or play in the rod bearings. Aren't you under warranty?

[thejeremyman9]

Originally Posted by BMWILUVU

Not great. My bet is leaking from the valves or rings maybe from impact of high-RPM pre-detonation timing being off or play in the rod bearings. Aren't you under warranty?

I had the same thought about warranty. This whole thread and sequence of events seems strange.

Changed 26k mile plugs on a stock car? Then plug mysteriously destroyed and blamed on knock and not a botched install? Weird marks on pistons and unclear boroscope of cylinder walls... compression looks good at first but then later leakdown fails...

Do you trust this shop?

[IraHayes]

Originally Posted by thejeremyman9

I had the same thought about warranty. This whole thread and sequence of events seems strange.

Changed 26k mile plugs on a stock car? Then plug mysteriously destroyed and blamed on knock and not a botched install? Weird marks on pistons and unclear boroscope of cylinder walls... compression looks good at first but then later leakdown fails...

Do you trust this shop?

And we still don't know if these are genuie NGK's or Chinese knockoffs. These need to be compared to known genuine NGK's for this car. As JimKDen pointed out, we can't clearly see the ground electrode to see if there was any contact made. It's also possible that when the plugs were changed, some kind of debris fell inside.

OP, did you change the plugs yourself, or did someone else?

[wesmeister]

Originally Posted by IraHayes

And we still don't know if these are genuie NGK's or Chinese knockoffs. These need to be compared to known genuine NGK's for this car. As JimKDen pointed out, we can't clearly see the ground electrode to see if there was any contact made. It's also possible that when the plugs were changed, some kind of debris fell inside.

OP, did you change the plugs yourself, or did someone else?

Would FPC Euro sell me Chinese knockoffs that are identical in boxing and finish to real NGK's for $15 each? I guess anything is possible... but I didn't buy spark plugs off Ebay or something.

I bought these exact plugs: https://www.fcpeuro.com/products/bmw...plug-ngk-96987

The car had a rough idle when I bought it. The plugs were changed as part of a regular tune-up I did myself, to include new OEM oil filter, air filter, and Liqui Molly 5w-30.

[thejeremyman9]

Originally Posted by wesmeister

Would FPC Euro sell me Chinese knockoffs that are identical in boxing and finish to real NGK's for $15 each? I guess anything is possible... but I didn't buy spark plugs off Ebay or something.

I bought these exact plugs: https://www.fcpeuro.com/products/bmw...plug-ngk-96987

The car had a rough idle when I bought it. The plugs were changed as part of a regular tune-up I did myself, to include new OEM oil filter, air filter, and Liqui Molly 5w-30.

So to be clear, all of these issues, including the knock appearing (and all subsequent events), started after you changed the plugs and did said tune up?

[wesmeister]

Originally Posted by BMWILUVU

Not great. My bet is leaking from the valves or rings maybe from impact of high-RPM pre-detonation timing being off or play in the rod bearings. Aren't you under warranty?

Another thought we had was the possibility of the piston extending past TDC because of either a a damaged rod or crankshaft, but the current TDC tolerance measurement came out perfect. Doesn't rule out a possible rod with "play" in it, but I would expect loud knocking if this were the case.

Rings are definitely a consideration at this point , but are going to require a tear-down to inspect. The borescope didn't show any immediate damage to the compression rings. It could be a serious blow-by problem from lower rings... which could then, in theory, amplify this super knock condition once the IATs get high.

Ah yes, warranty. I bought the car "as-is" from a BMW dealership. It had the typical 75 point inspection and looked good mechanically and aesthetically when I purchased it. I went ahead with an aftermarket warranty from the dealership, that BMW honors at all of their dealerships. The car might end up back there, depending on what my mechanic finds next...

Sure I trust this mechanic shop. They are one of the best independent BMW shops in Southern California. They are being very pragmatic and working with BMW tech support directly through ISTA+ on the diagnosis. But I think it's safe to say that this case is highly unusual, so I thought I'd start a thread to see if anyone has any insights out there.

Again, if anyone is interested in helping with a little more "arm-chair mechanic" analysis... I have the diagnosis report online I can share PM. I just don't want to plaster that link on the internet.

[wesmeister]

Originally Posted by thejeremyman9

So to be clear, all of these issues, including the knock appearing (and all subsequent events), started after you changed the plugs and did said tune up?

Negative. The rough idle and hesitation at a higher RPM was there probably from the beginning. Some environmental factors at play here, especially considering I never revved the car up to 5K rpm when it was fully warm when I first got. There was hesitation getting on the freeway every like 1 in 20 times... but it was never a full blown "super knock buck smash cylinder shutdown" feeling until recently.

So basically, it has gotten worse with time. Irrespective of the new spark plugs.
The new spark plugs DID help ease the rough idle though

[thejeremyman9]

Originally Posted by wesmeister

......
Ah yes, warranty. I bought the car "as-is" from a BMW dealership. It had the typical 75 point inspection and looked good mechanically and aesthetically when I purchased it. I went ahead with an aftermarket warranty from the dealership, that BMW honors at all of their dealerships. The car might end up back there, depending on what my mechanic finds next...
......

I understand starting a thread for sharing info and getting opinions, but why did you not immediately go to BMW if you have a warranty? Aren't you just burning money with this indy?