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WarriorX 07-04-2010 02:20 PM

Cracked Porcelain
My 08 WRX has about 55K on it when I decided to change my own plugs and researched the do's and dont's. Bought OEM plugs from the dealer and assembled the tools I would need, including a torque wrench. Replaced all and put it back together, making one bonehead mistake of not verifying the gap before putting the new plugs in. The car runs fine except when under stress, under a pull at higher RPMs or when a rapid WOT I get a misfire. There haven't been any CELs so far. I decided to go back in and verify the gap and reinstall the plugs when. In the process of pulling the plugs and reinstalling, I noticed a piece of the plug's porcelain inside the plug well, I haven't been looking at the rest of the plug only the gap. BTW, all the gaps were about 0.030. I pulled that plug back out and it was missing some of the porcelain. I then moved on to the next plug (passenger side, front) which was the last of the four to be checked for gap and this porcelain was cracked on two sides along the entire length. I think this may be the cause of the occasional missfire but I'm not sure why the plugs are cracking in the first place. Like I said, I'm torquing the plugs down to 15ft. lb. Could I be torquing the coil bolt too tight? Any other ideas? Anyone else experience this?

06subiSTi 07-04-2010 09:32 PM

I have broken the porcelin on the plugs of my 69 ford. usually happens gettin the plug out and the socket slips

wagonracer 07-05-2010 01:09 PM

I once got a set of NGK's that looked like they had been dropped The porcelain didn't break off, but the spark arced through and toasted the wire (this was on an old 2.2 with out coil packs at the cylinder) Personally, I would replace the whole set. Use anti-sieze and the correct torque specs You may have just gotten a bad set like mine.

man show 07-06-2010 10:36 AM

There's been some debate about whether or not using anti-seize on our plugs is a good idea. I did a bunch of reading a little while back and here are some things I found:

- Anti-seize is a lubricant
- Applying anti-seize to threads changes their torque values
- Torque directly affects the spark plugs’ ability to transfer heat out of the combustion chamber. A spark plug that is under-torqued will not be fully seated on the cylinder head; hence heat transfer will be slowed. This will tend to elevate combustion chamber temperatures to unsafe levels, and pre-ignition and detonation will usually follow. An over-torqued spark plug can suffer from severe stress to the Metal Shell which can distort the spark plug’s inner gas seals or even cause a hairline fracture to the spark plug’s insulator. In either case, heat transfer can be slowed.
- Most NGK plugs come from the factory with a shiny silver metal coating (Trivalent coating, a form of “anti-seize”)
- “Anti-seize” or “Anti-corrosion” coatings are applied to threads to prevent them from seizing to the head and reduce the risk of pulling out the threads
- If you reinstall a set of NGK plugs, it is recommended to use anti-seize because when you remove the plugs from the head, some of the Trivalent coating will be lost
- Many anti-seize compounds contain graphite
- Graphite corrodes Aluminum almost instantly (even more with added heat)
- WRX/STi spark plugs should be torqued to approximately 15-19 ft/lbs

- The best method is to apply a small amount of copper-based anti-seize and using the gasket-touches-plus-1/4-turn tightening method
- It is unnecessary to apply anti-seize to the threads of NGK plugs because of the Trivalent coating, but it certainly shouldn’t hurt anything unless you over torque them
- NGK does not recommend the use of anti-seize for spark plugs with special metal plating


newtothegame 07-06-2010 10:47 AM

We use (not me) anti-seize on bolts and stuff on helicopters. We have a conversion chart for parts that have anti-seize used or not used. I can try and find that chart and see if it can cross with stuff like this. Its just another option I suppose.

WarriorX 07-08-2010 11:57 AM

Cracked Porcelain
Unfortunately, I uncovered all of this while I was on the road for the 4th holiday and I had to get my car back together and in good enough working order to travel two states away. The dealers weren't open and none of the local autopart stores carried the NGK so, I to settled on AutoLite Iridium plugs at 2/3rd the cost. I figured I would run these until they showed some problems and switch back to NGK. After replacing all four of the NGKs with the AutoLites I was throwing a CEL and missing badly. I didn't have my AP with me, another bonehead mistake, so I took it to the local Autoparts store for a code check which turned out to be plug 4 misfire. I was getting desperate and needed to head back home the next morning, 375mi trip and it was already getting late. I called the local dealer and scheduled service. The tech found two of the plugs I just put in were cracked with the cylinder #4 plug cracked around the base. The other plug was cracked closer to the top of the porcelain and was not causing a problem, yet. He replaced these with NGKs and the car runs fine now. I told him how I was attempting to change these, using the methods detailed in several WRX forums. He explained his process of removing some of the engine peripherals along with motor mounts and swinging the motor up about 6 inches. He couldn't imagine how anyone would change these plugs without going through this process. I not exactly sure what all he had to remove or loosen in this process but, I do specifically remember him saying the engine was lifted about 6 inches.
So, long story short...I'm a mechanical clutz. If something can be broken, I will break it. Seriously, I've been changing plugs in a variety of motorized vehicles for over 35 years and I don't ever recall breaking a plug.
Thanks for the replies.

man show 07-08-2010 11:14 PM

Nah, probably just bad luck. If I were to lift my engine 6 inches, that would make changing the plugs so much simpler. I just do it the hard/fun way and use a random combination of universal joints, extensions, and flexible extensions until I get the damn things changed. I think I found a combination that works, but I can never remember it, so it's always trial and error, but I always end up getting it done.

The plugs don't need a whole lot of torque, just the slightest bit of snugness will get the job done... however you want to measure that. With or without antiseize - just snug em gently and they shouldn't crack.

fuapiti 07-09-2010 09:29 AM

How often should we change the spark plugs?

(05 2.0 WRX)

man show 07-11-2010 08:18 PM

[url=]Subaru maintenance schedules and new car break-in period[/url]

According to the factory suggested maintenance schedule, they should be changed every 60k miles. I'm pretty sure the stock plugs are NGK Iridiums, so they should be good for at least 60k miles.

- Copper plugs last 10-15k miles
- Platinum plugs last 30-60k miles
- Iridium plugs last 60k miles

If you choose to use copper plugs (which are arguably the "best" as far as performance and the "worst" as far as lifespan), you should probably change them about every other oil change, providing you change your oil every 3k +/-.

There are many schools of thought out there though. If you're professionally tuned, I'd check with your tuner first and probably do whatever they say. If you're just trying to keep up with maintenance, you probably can't go wrong with 60k intervals and NGK Iridiums (stock heat level) - which is what I'm doing with mine.

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