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Discussion Starter #1
Guys - this is for the database so you are forewarned of what one has to do if a spark plug snaps off. Those 10mm plugs are fragile. I was all set to do the first big service on my 2014 -- belts, valve clearances, etc. The plug on the front cylinder snapped off. (And the auxiliary plug, accessible at the L/H side, was cracked.) So I envisaged that it was cylinder head and barrel off, which meant removing the airbox and injector assembly and the exhaust. I knew that even if I took the head off, the plug stub was down a long tunnel and it would be difficult to get it out even then. So I looked at the anatomy of a spare plug when snapped off. I was able to chip away at the porcelain inside the body of the plug until there was enough depth to insert a bolt extractor into the plug body. This took a while but I used a pin punch to crack the porcelain bit by bit, removing the bits with a long screwdriver. I sprayed penetrating oil into the tunnel and left it for a few days.

Eventually, after some quarrying, and several attempts with various sizes of bolt extractor, I got some 'bite' on the bolt extractor, which I made an extension for, using sockets, so that I could hammer the end. With a 3/8" wrench, I was just able to exert enough force without using an extension lever. That's how badly the plug was stuck. The stub gave way and hours of time and expense were saved. I am certain the plug had not been disturbed since leaving the factory. (I got the bike in mid-2016 with low miles.) There was a lot of corrosion even though the plug cap appears to offer a weather-proof seal.

BUT--you don't have to go through this ordeal if you want to disturb a plug when doing your own service! If you see lots of rust and if the plug is resisting 'normal' force of your plug wrench, then read the thread on here where the shop mechanic sprays penetrating oil down the hole, leaves it for while and then starts the engine to get it good and hot. The plug is more likely to come out then.

It's good practice to replace plugs at a major service, otherwise you risk a failed plug, buried under mountains of bodywork and many hours of needless stripping.

Lessons?
- change your plugs more frequently than every four years!
- use a small smear of copper grease around the base of the plug threads, but not too much in case it flows down the threads and fouls the electrodes.
- perhaps seal with silicone around the top of the plug cap.
- don't apply undue force on these little plugs to remove them. If they won't budge, spray penetrating oil liberally down the tunnel and warm the engine -- then wrench. The problem is that corrosion over the years weakens the thin plug body and it then snaps.

Pics attached. The rear cylinder tunnel is pictured to show the depth, and the recess at the bottom into which the plug sits. The bolt extractors are not reverse thread 'easy outs' which break all too often. These seem to made of stronger stuff but you have to hammer them in.

Dave
 

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I use the type of anti seize with copper in it.
 

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Great insight on this problem. I take it that the plug snapped off and the lower portion of the plug did not have hex wrench flats? Its too bad that there aren't flats on the lower portion. The fact that the plug could structurally fail like that is concerning, but I suppose the underlying factor was the thread seizing and its effect on removal torque.
 

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Any idea how that level of corrosion happened? That sparkplug looks like it was in standing water, almost like the plug bore got immersed and the water was trapped inside by the boot.
 

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Great tips! I would have thought the hex wrench portion of the plug body is solidly attached to the base threaded section. It looks it was, but it got corroded and broke off? Good thing you were able to extract the rest of it without resorting to major surgery. I've had similar close calls working on various vehicles...
 

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Just did my 15k service on a 2014. My horizontal center was also rusted. Mine didn’t break thank goodness. I’m going to be super careful to never spray water there when cleaning. It’s a design flaw apparently. No way for water to get out and the seal, doesn’t.
 

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I’d add that if you snap the left vertical plug I think the engine will have to come out. I see no other way to get to that one.

NGK recommended against anti-seize so I didn’t use it but I’m seriously thinking about going back and adding it.
 

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Any idea why NGK would do that ? The only reason I can think of is that they feel anti seize might affect the grounding of the plug to the head, which is why I use the copper type. I would assume the copper would help maintain a good ground.
 

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Their website said something about their plugs already having a coating to prevent issues. Some negative to it but don’t remember what it was. Torque maybe.

edit: It was a technical bulletin, showed how the compound led to over tightening and was not necessary with their plated plugs. I emailed them just now, curiosity is up..
 

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Got a quick reply. NGK says:

Hello,

Thank you for your E-mail. NGK does not recommend anti-seize, our plating prevents seizing. Recommended torque on that part number is 7.2-8.7 Ft./Lbs. dry.


Regards,

Michael Durocher
Technical and Training Specialist
NGK Spark Plugs (USA), Inc.
(248) 926-7104
Mobile (248) 893-9080
[email protected]
 

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Discussion Starter #13
Guys, first, my apologies for not coming back sooner to all of you who replied. I failed to tick notification of replies. Where do I find this check box?

Mabrungard and Ducorama-- Yes, the plug snapped off below the hex, leaving the stub and threaded portion in the cylinder head. Yes, it looks as if the severe corrosion weakened the body of the plug. I think the main lesson is not to neglect the spark plugs in the front cylinder at the least and perhaps check them every two years. My bike was going so well that I thought I would delay replacing them until the big service!

So, next time, I will get the motor good and hot, pull the rad and try the plug while the cylinder head has heat in it. Also, I would definitely not re-use the plugs, even if you change them frequently. The little gasket/washer will have compressed and you will have to torque it down more than necessary. This could add to difficulty down the road...
 

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Discussion Starter #14
Old Rider -- It's NGK. Not only was the central plug badly corroded, but the second plug's porcelain was cracked underneath the plug cap.
 

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Discussion Starter #15
I would only use anti-seize on the very top of the threads. However, I have since heard that graphite grease can also work here. The main thing is to apply it sparingly. Some plug manufacturers don't recommend thread lube because lubing the threads can result in a greater clamping force than recommended being applied, thus placing more strain on the plug and its threads. I'd make an exception in this case, though!

Snapped off plugs are more common than I thought, because I did some searching on the web after mine broke. Ducati is not unique in this regard; it also happens in some cars.

Shorton -- thanks for the torque figures from NGK.
 

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I’d like an explanation of your use of anti seize ? Not criticizing just wondering about the logic. If you don’t coat the threads then you don’t reduce the chance of seizures. Using a little at the end would be like only using the top half of a condom, wouldn’t it ?
 

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Discussion Starter #17
I’d like an explanation of your use of anti seize ? Not criticizing just wondering about the logic. If you don’t coat the threads then you don’t reduce the chance of seizures. Using a little at the end would be like only using the top half of a condom, wouldn’t it ?
Ha, ha!

This is my natural caution kicking in here. Let's say you smear some graphite grease on the topmost half of the threads, this is where corrosion is most likely. And also, it is then less likely to flow down the threads and foul the electrodes.

From this experience, I would say that by far the most important thing is to replace the spark plugs more regularly than I did, but especially the front cylinder. The rear cylinder on mine was pristine because it is not exposed to the weather. Replacing both front plugs regularly should reduce the need for anti-seize or thread lubricants. Also, not giving in to the temptation to over-tighten the plugs!
 

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I tighten until I feel the washer hit, then feel it crush, then resistance. Stop then. Used plug, until I feel the washer hit, then I feel resistance, stop. No need to get carried away, you’ll hear it if it leaks.
 
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