sparkplug

PULL THE HEAD. And put antiseize on the plugs when you put them back in (just a WEE bit)

Long reach plug, threaded only half way COULD break off part way down

- wrong plug for the application - Only seen it on AC plugs.

TDC on overlap - both valves open to allow LOTS of air flow and keep the chips close to the hole so the airflow can pull them out.

Grease whatever tools you use so chips stick to them. If drilling, drill SLOW and "peck" so you pull all the chips out of the hole with the greased bit.

But to be SAFE, pull the head.

I've seem a fair number of tapered seat plugs (specifically FORD, but also a few others) snap off at the top of the threads. Some AC 14mm long thread plugs were threaded ONLY on the bottom half. I've seen these snap off low in the hole as well. In over 38 years of wrenching I've broken a few plugs off - but VERY few. I learned early to take it easy, use lots of good penetrant, and take my time. It ALWAYS takes longer to take out a broken plug than to finesse it out in the first place (possible exception is an air cooled flathead)

You use a strip of cloth about two inches wide. Soak it in motor oil and insert it through what hole there is. I assume that there is a hole since spark plugs are usually hollow down by the threads and that is where he said the plug broke off, midway down the threads. The assumption here is that the center core of the plug came out and he just has the metal threads in the plug hole. Otherwise this trick won't work. I used it one time and it worked quite well.

Jim

According to PeterD :

[ ... ]

Actually -- it is cross-posted to three newsgroups:

rec.crafts.metalworking rec.autos.4x4 alt.autos.toyota

if you look at the "Newgroups: " header.

And in at least some of the newsgroups, difficult questions are standard.

Enjoy, DoN.

I agree, the left hand drill is best way to start working on many broken fasteners. If you are going to have to drill it anyway, you might as well use the left hand drill and give it a chance to come out before you do anything else.

I've had fairly good luck with easy-outs. You have to know when and how to use them, though. If a screw snapped because it bottomed out in the hole or was cross-threaded or corroded into place, the easy-out is not as likely to be effective as it is if the screw failed due to shearing or tension. The most common mistake people make with easy- outs is using too large a size. The thinner the walls of the broken screw are, the more likely the easy-out is to expand them and lock the threads. While the larger easy-out is of course stronger, it's better to first try a smaller size that will not expand the screw. There are some non-tapered screw removers with straight splines that work without expanding the screw.

It's hard to imagine why a spark plug would break in the middle of the threads - usually the undercut at the shoulder is the weak area.

Two points in this thread got my attention:

1. Never-Seize. I've heard at least once that there are good reasons NOT to use it on spark plug threads, but I can't remember what they were. Yes or no?

1. Better to remove plugs hot or cold? Posters in this thread have it both ways.

John Martin

Autolite says not to use anti-seize becasue it can contaminat the spark plug insulator and short out the plug (anti-seize includes metallic elements). NKG says it is not necessary with their plugs becasue of the plug construction and they recommend against its use becasue the lubricating properties of the anti-seize can lead to improper torquing of the plugs.

In an aluminum head you should remove the plugs when the head is cold.

Ed

We've all learned that a hole in a block of metal gets larger when the metal expands and the coefficient of thermal expansion for aluminum is about twice that of steel, so I'd expect the diametrical fit to get looser when the head gets warm.

But I'm willing to learn something new every day, so why do you say you should remove the plugs when the head is cold? (Maybe it has something to do with the relative change in thread pitches at different temperatures? Naw...)

Jeff

I am actually repeating the recommendations from shop manuals and plug manufacturers (remove plugs when cold). The question is, what has expanded more when hot, the heads (making the hole larger) or the plugs, making the fit tighter. Aluminum expands at a higher rate than steel, but it also cools faster, particularly on a water cooled engine where the water in the head should limit the peak temperature of the aluminum head to a lower value than the steel sleeve of the spark plugs. As things cool, I suspect the aluminum head will cool much faster. So it may be that the fit is actually tighter when the head is hot, not looser as you are suggesting. But even if it is isn't, what happens when you screw the new cold new plug into the hot (or at least warm) aluminum head? The thread fit will be looser than designed and this might make the torque applied incorrect, or make the thread easier to strip. The original plugs and head were cold when assembled, so it only makes sense to me that the same is true for the replacements.

Ed

I think the aluminum may be weaker and have a greater tendency to sieze or gall when hot, but I am not sure of that.

Don Young

"C. E. White" (clip) Aluminum expands at a higher rate than steel, but it also cools faster, particularly on a water cooled engine where the water in the head should limit the peak temperature of the aluminum head to a lower value than the steel sleeve of the spark plugs. As things cool, I suspect the aluminum head will cool much faster. So it may be that the fit is actually tighter when the head is hot, not looser as you are suggesting (clip) ^^^^^^^^^^^^^^^^^ I think that "hot" refers to an engine at operating temperature. "Cold" refers to an engine that is essentially at ambient temperature. The rate of heating or cooling does not enter into the discussion. Since aluminum has a higher coefficient of expansion, it will result in more clearance around the threads on a hot engine.

But note that the head and plug expand and contract in a vertical direction also. The head gets thicker when it is hot, more than the plug expands, so the gasket is more compressed. That sounds like a plus to me.

When you are changing plugs you are not talking about an engine that is "operating." You are somewhere between steady state operating conditions and cold. If you try to change the plugs before the engine is "cold," the temperature of the parts is changing constantly as you work. Under operating conditions I am guessing the body of the plug is much hotter than the surrounding metal of the cylinder head. Part of the plug is actually down in the combustion chamber. There is discontinuity between the plug and cylinder head, adding an impediment to thermal transfer. The actual head has internal water passages, so the maximum head material temperature is limited. When you turn the engine off, the aluminum head cools much faster than the spark plug. The effect on the forces needed to remove the plug is not clear to me, but it is certainly changing as the engine cools. I just can't see how it is better to change the plugs during this period of time (as the engine cools) that waiting for it to reach ambient conditions.

Ed

Danny G. wrote in article ...

The situation as the OP described it is quite common.....and the often DO break right at the top of the threads.

Steel spark plugs in aluminum heads can create some electrolytic activity.

100,000 mile plug change intervals simply give this activity longer to do its job.

Stop by virtually ANY professional automotive machine shop, and there's a good chance that there is a head or two that have been dropped off and sitting in the "To-Do" pile, awaiting a spark plug threadectomy.

insulator and short out the plug (anti-seize

becasue of the plug construction and they recommend

lead to improper torquing of the plugs.

expands and the coefficient of thermal expansion for

get looser when the head gets warm.

should remove the plugs when the head is cold? (Maybe it

temperatures? Naw...)

manufacturers (remove plugs when cold). The question is,

plugs, making the fit tighter. Aluminum expands at a

cooled engine where the water in the head should limit

sleeve of the spark plugs. As things cool, I suspect the

tighter when the head is hot, not looser as you are

new plug into the hot (or at least warm) aluminum

torque applied incorrect, or make the thread easier to

sense to me that the same is true for the

You let the engine cool down first so you don't get burned right.

Much snipped......

This thread has been going on for the better part of a week. I wonder, did the guy ever get the sparkplug out, and if so how did they do it?

Bruce in Bangkok (brucepaigeatgmaildotcom)

The OP made 2 posts on the 18th (and maybe another), and the other subject line is: Plug broke-off in head, now what??

..where he says the dealer's mechanic said the plug broke off while trying to remove it, and that the "Initial estimate is $1700"

That's a fuctup situation to be in, and the resolution needs to be negotiated cautiously, to obtain favorable results, IMO. It's time for a lawyer, sorry situation but likely, if the dealer won't take care of most of the cost of the repair, and also warranty the work.

In a GM dealership garage in the '70s, that type of problem was a Code 59, damage incurred as a result of service work. The shop eats the cost.

The OP might be busy looking for another vehicle.

WB ......... metalworking projects

Rather than pull a head or worse case replace the head, he should look for another vehicle???????

You can't be serious.

Depending on the vehicle, that is write off territory....

I got a great Volvo Wagon that way a few years back for $50.00. The headgasket was blown and the cost to fix it was in the same range. The owner basically scrapped the car rather than pay that.

My son and I changed out the gasket in an afternoon and drove the car for 4 years, then sold it for $50.00. The AC even still worked...

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06 (More Off Road album links at bottom of the view page)

This one according to the OP is a toy 4 runner. I guess I figure that if it is worth having sombody put in a set of plugs, it's worth a r&r of a head.