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Broken spark plug...

Posted by ashelton80 (My Page) on
Tue, Dec 23, 08 at 19:06

I consider myself pretty handy, but I have a real winner that is givin me a fit.

I was going to do a routine spark plug/wire change...simple, 30 minute deal....until one of them snaps off, leaving only a hollow thread and electrode firmly in the head....

Its aluminum, so heating is out. And EZ out won't budge it and the last thing I need is to break one of those toughies off in there.

I know the optimal solution is to remove the head, go have it remachined...blah blah blah, but we are talking a 97 s-10 with almost 200,000 miles on it that already needs several hundred dollars worth of repairs on non-mechanical stuff so spending more than its worth isn't an option.

I have decided to HeliCoil it. What size drill bit should I use to remove the remaining plug and the old threads, so I can retap this thing? The spark plug thread is 14mm, so I assume I need to go just a tad bigger to tap and insert my helicoil, yes?

Any help is greatly appreciated!


Follow-Up Postings:

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RE: Broken spark plug...

There are ez outs and there are ez outs. See what the Snap On guy has. Ridged makes good ones too. Good ones ain't cheep. Bet you won't break those. No matter what you've got to get the old plug out. IF you damage the threads in that process, then you can think about a heli coil. The parts guy will can get you the right size coil, drill bit, and installation tool.

I don't like the do it on the engine idea at all myself. How are you going to drill without getting shavings in the cylinder?


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RE: Broken spark plug...

Honestly, I don't like that idea either, but I can clean it out for the most part. I could justify buying another vehicle before I could justify putting more money that this one is worth back into it. Hey, on a newer vehicle I would definitely put the bucks down to do it right, but the way this one is I'm willing to gamble a bit. Realistically, if i was going to have the head pulled, I would almost be ahead to have the thing rebuilt while the motor was torn apart, and it's just not worth it to me.

If you coat the taps and bits with grease it will catch most of the shavings, and I have a telescoping magnet to retrieve some more, and finally a shop vac with a microhose that will fit into the hole to get even more, and then turning the engine over with the plug out should blow out most of whats left. I won't skimp on the effort to get everything possible out.

It's been an insanely good vehicle for the money I have in it, and I have gotten my money's worth in the years of troublefree service it's given me.


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RE: Broken spark plug...

Ho Boy! You do have a problem. I've never encountered a sparkplug that broke off the hex part - rounded off the hex, or snapped the insulator - yes.

Its a given that some debis will fall into the cylinder, and some of it may be the insulator which is very abrasive.

You stated that you could not apply heat because the head was aluminum. You may be able to, but you can not go blasting away with a gas torch. Since this is an end of life repair for the engine, I'd try some heat. I suggest using a high wattage heat gun, for example, one made by Master. Warming up the head several degrees around the spark plug may be helpful since the thermal expansion of aluminum is greater than steel.

Use caution when using a heat gun around the engine compartment. The heater element gets hot enough to ignite fuel.

If you can apply penetrating oil without getting any in the cylinder, it may help. The effect of penetrating oil in the cylinder is unknown to me. In addition, one has to be cafeful to use only fluids that will not harm the catalytic converter.

Warming up the metal and then applying penetrating oil may be helpful.

When you go to blow out the cylinder, it would be nice if both valves were closed, to keep from blowing stuff into the exhaust or intake manifold. The piston does not have to be all the way up to top-dead-center to close the valves. If practical, close the valves before you begin the job, but do not move the piston all the way to the top to leave working space for taps and EZ-outs.

Debris in the intake manifold may damage the engine when it is started. It gets sucked into the cylinder and depending on its size and hardness, can do much damage.

It is advisable to remove the head. If you are doing the work yourself, it'll cost you your time, a set of gaskets, and new head bolts, and you might be able to extract the plug without ruining the existing threads.


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RE: Broken spark plug...

For what I am about to type, I ask that you make a donation to the Epilepsy Foundation.

First, there are specific kits available for repairing this failure. Its not as uncommon as some may think because with spark plugs that can last as long as they do, and ignition systems that actually simply keep firing the cylinder even when the electrodes of the plug have eroded away, we see seized plugs quite often.

In the kit there will be instructions as to what sized drill bit will be required, more expensive kits will include the drill bit, and tap. Make sure to select a "tapered insert" that matches the thread length of the spark plug exactly. Too short of one will allow the plug to overheat, and the cylinder will detonate and melt the piston. Too long, and well you'll know right away.. VBG...

DO NOT use a standard helicoil, they are not designed for such a repair, and will allow compression leakage around the threads. they also could not cover the plug threads correctly, and again result in the plug not being cooled correctly.

Here is the part of this that is worth $$$$.

Now go get the shop vac, and connect the hose to is as you would use it as a leaf blower. Connect the shop vac to the tail-pipe, and turn the engine over by hand to open the exhaust valve just enough that the shop vac blows out of the engine through the cylinder you are going to work on.

Of course protect your eyes, the rest of your body and any part of the engine were machining chips will be an issue, because as you work, the metal chips will be blown out all over the place.

Now follow the instructions as to how to drill out the old plug, thread the hole, and install the insert and stake it.

If you want to roll the engine over to try and ensure no chips went in after you have cut the new threads, prior to installing the insert, there is no reason you cannot do that. Disconnect the ignition module so that you dont have spark while you do.

An "Easy Out" is exactly what its name implies, it will remove a broken bolt that will come out easily. Otherwise you risk breaking a very hard, brittle tool off in the "bolt hole", which of course is the spark plug hole this time. Typically for an easy out to grab, it has to wedge into the bolt being removed, by the time it would likely grab a broken spark plug, it actually expands it and makes it tighter.

I've seen people attempt to heat and cool the broken plug, and there has been reports of success when this is done. I've seen people saw through the sides of the plug and remove it in pieces. Trust me, that takes a LOT of effort, and then you still end up resizing the hole and installing an insert.

Here is a link that might be useful: One such thread repair system. There are others too.


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RE: Broken spark plug...

Thanks yall for the informative responses! I really appreciate it!


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