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Ford Spark Plugs Break During Removal

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Amclaussen
User Rank
Platinum
Re: Bad basic Plug design.
Amclaussen   3/25/2015 1:08:55 PM
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Maybe I didn't explained myself enough. I was talking about the glow plugs because, just after ignition is initiated, both types of plugs simply seal the combustion chamber from the combustion gasses ("plugging" the chamber).  The differences thus, are not relevant to the problem of binding and breaking of the spark plugs.

The thing is that in the Nelson glowplug the threads are located above the conical seal, which prevents the ingress of gasses into the threaded portion. Even when the Ford design correctly placed the threads above the seal, they failed miserably by placing the lower shell portion under the seal, allowing combustion products to form deposits that bind this lower shell to the engine head.  To compound this example of bad design, another set of extremely *intelligent* sparkplug designers decided to fabricate the plugs with a crimped connection that breaks.  Monkeys monkeys monkeys!

doug_linkhart
User Rank
Silver
Re: Bad basic Plug design.
doug_linkhart   3/24/2015 5:39:47 PM
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Thanks, Amclaussen for your comments.

For those who may not know, glow plugs differ from spark plugs in that they don't require any electrical power after they are hot, as the combustion process keeps the glow plug hot.  Typically glow plugs are heated intially by a low voltage, so they do not require high-voltage insulation.  Because the insulator does not have to stand off any significant voltage, it can be flush with the combustion chamber wall.

Spark plugs, on the other hand, require high voltage pulses during operation.  The combustion side of the insulator typically has a rather long, conical shape.  This provides a long surface creep path for the high voltage so there is no voltage breakdown on the insulator surface.  If the insulator were flush/flat, the creep path would be much shorter, leading to voltage breakdown and fowling.

The heat range of the spark plug can be controlled by varying the length of the insulator cone, which also serves the purpose of removing heat from the inner electrode.  The base of the cone (the end away from the sparking end) is in contact with the metal shell of the spark plug.  It is in this area that heat is transferred from the insulator to the shell.

Heat is removed from the shell, in turn, by transfer to the cylinder head.  This is where the spark plug shell needs to make good contact with the head; it is where the seal is located.  If the seal were located close to the sparking end of the plug, heat transfer would be poor because the path would be through the insulator, then back towards the combustion chamber via the shell.  This would force the design of the insulator to have a shorter cone, which would increase its susceptibility to voltage breakdown.

I don't mean to say that the spark plugs used in modern IC engines are of the best possible design- I thought I would explain why they are the way they are- it's for temperature control, voltage breakdown resistance, and minimum cost, among other factors.  There may be designs available that offer better performance, but are not used for one reason or another.

Amclaussen
User Rank
Platinum
Re: Bad basic Plug design.
Amclaussen   3/24/2015 3:11:40 PM
NO RATINGS
,Apart from a bad manufacturing practice (having a crimped shell connection prone to breaking), please let me comment on the basic geometric design of these plugs.

Apart from loving all car care and performance modifications, I enjoy model airplane building and flying.  As many young boys in the 60's, I started into that hobby with the old COX and WenMac small 1/2A engine powered plastic airplanes, 0.049 cubic inch glow plug engines.

Years later I became a serious modeler, and used a lot of different engines in many sizes.  There is an engine design that is truly outstanding for its power, The Nelson.

Nelson engines use a different plug geometry: the pressure seal is at the bottom of the plug... the plug threads are above the conical seat, and therefore, no gas can actually get into the threaded space and become a temporary "pressure leak" that robs the engine some power, all the combustion gasses are kept inside the cylinder, period.

As soon as I saw the Ford sparkplug design, I thought: What a dumb design!, even when they somehow improved the geometry by placing the conical seat UNDER the threads, they completely ruined their design when they placed a long lower shell with a gap between it and the engine head, that is an empty space where combustion gasses get into and back again with energy losses, and worst: form deposits.

It has always puzzled me WHY auto manufacturers place most sparkplug threads UNDER the pressure seal, be it a conical seat or a ring gasket.  At high engine speeds, the combustuion gasses get into the threads and are temporarily stored there and then released, after the pressure peak and therefore, they represent a kind of pressure leak.

By placing the conical seal at the bottom of the plug, Mr. Nelson got it right.  Maybe the monkeys at Ford could hire him for a change!  Amclaussen.

 

William K.
User Rank
Platinum
Re: I think you misscope the job
William K.   3/23/2015 7:12:00 PM
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Given that the problem is known, it would make a lot of sense to pull the plugs out at 30K and 60K moles, and re-install them with a coating of anti-seize compound. 

And the other suggested posting, the one using the loosen-lubricate-tighten, then repeat, approach is certainly a preferred method. Of course the more sensable approach would have been to design the package differently to avoid the problem.

doug_linkhart
User Rank
Silver
Ford TFI Reliability
doug_linkhart   3/23/2015 5:07:41 PM
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@ragtoplvr

I agree that the TFI module design and designed location were poor from a reliability perspective.  I suspect that the designs met their cost target, so from a cost perspective, the designs were probably "good."

The TFI modules are sensitive to temperature.  I have a 1991 Mustang that has the TFI system.  On a hot day, after the car had been driven for an hour or so, the engine would stall and could not be restarted (no ignition).  Some of the early F-body Mustangs had issues with overheating, which just aggravated the problem.  When the engine would stall, I would pull over to the shoulder or the nearest parking lot, raise the hood, and wait about 10 minutes.  Usually after about 10 minutes of cool down, the car would start, and I would be on my way again until the TFI module got hot enough to fail again.

Replacing the TFI module with a new one (Ford/Motorcraft ones are more reliable than the aftermarket replacements) would sometimes increase the length of time that the car could be driven before it would stall.  Ultimately, I relocated the TFI module off the engine to the inside of the left fender.  In this cooler location, ignition failures are far less frequent.  Another solution to the TFI problem, which I chose not to use, is to replace the distributor (and modules) with an aftermarket one.

GM has had its share of problems as well.  I had ignition coil problems with a 3.8-liter V-6 Buick motor back in the 1980s.  The coil, which was located in the distributor, had an intermittent primary connection.  I diagnosed the problem, and planned to replace the coil in a few days when I had time- I managed to get the car running by wiggling the primary wire. 

As bad luck would have it, the next day the car stalled in a relatively remote area.  I could not get the car running by manipulating the primary wire, so I walked to a gas station and asked the tow truck driver there to tow the car to my home.  The guy drove me back to my car in the tow truck, and then asked me what was wrong with the car.  I explained that the ignition coil was bad.  He then wanted to know how I knew the coil was bad, so I explained the diagnostic procedure, which was as simple as connecting a test light to the primary terminal and cranking the engine. 

The tow truck driver said, "You need a new distributor.  It will be about $350, and we can do it for you tomorrow."  I argued that it was not necessary to replace the entire distributor; only the coil was bad.  He then said, "We don't do that weirdo crap, we just replace the whole distributor."  I told him that I just wanted the car towed to my home, and I would handle the repairs myself.  He said that he had to go back the the gas station to let his boss know where he was going, then he would come back to tow the car.  After I waited about an hour, it began to sink in that he wasn't coming back.

I decided to try wiggling the primary wire one last time before going for a longer walk to find another tow truck.  My luck changed, the car started, and I drove home.    

RightStuff
User Rank
Iron
Re: High Temperature Anti-Seize
RightStuff   3/23/2015 4:37:43 PM
NO RATINGS
The MSD and Bosch spark plugs I used were pre-coated.  Package warned not to add any additional chemical. 

Critic
User Rank
Platinum
Spark Plug Change at 60k Miles
Critic   3/23/2015 4:24:17 PM
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Birdman, will you have your plugs changed again at 120k miles?  If so, you nearly doubled the cost of spark plug replacements by doing it early, but changing the plugs early is a way to make it easier to remove them.

doug_linkhart
User Rank
Silver
Re: High Temperature Anti-Seize
doug_linkhart   3/23/2015 4:14:04 PM
NO RATINGS
@RJE:  in the TSB, Ford recommends that the shells of the new plugs be coated with a thin layer of high-temperature nickel anti-seize compound before installation.  You posted sound advice!  

 

ragtoplvr
User Rank
Gold
Re: I think you misscope the job
ragtoplvr   3/23/2015 4:11:28 PM
NO RATINGS
The ford thick film distributer module did not fail because it was mounted on the distributer which is not the hottest place.  GM mounted the ignition module inside the distributer from 1975 to the mid I think 2005 and while they fail on occasion, it was not anything like Fords crummy design problems.  It was simply a  poor design.

 

Something they repeated on the high voltage drive for the Peizo diesel injectors.

 

Rod

Ron Morey
User Rank
Iron
Modular engine tip and comments
Ron Morey   3/23/2015 4:06:12 PM
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I went through this same problem. Some commentators need to recognize that these spark plugs are expensive and last much longer than the old regular plugs. The Motorcraft plugs last 160 K kilometers or 100M miles. If the plugs are broken there are several manufacturers of tools that remove all the pieces. I had to buy one-it is impressive but it is frustrating to have to buy a $100 tool to remove spark plugs. I bought some Champion plugs the first time. $18 ea and they lasted 40000 km. Recently I did the replacement again. The spark plug holes must be blown out with compressed air before attempting to remove the plugs. If you don't you will get dirt in the cylinders. I found that if the engine is warm and the plugs are "cracked loose" this helps immensely. Turn them slowly less than 1/8 of a turn. Drop about 1/2 cap full of carb cleaner and wait a few seconds. Tighten the plug and reverse. Continue this process and feel how the plug moves. Add carb cleaner as needed. I only added small amounts to make sure I didn't wash any particles into the engine. As the plug loosens move it until you feel restriction. Do not force it. Then turn tighter until it moves freely. Back it out again-etc, etc. The first time I tried this with the original plugs I broke one plug. That was the one I tried to loosen when the engine was cold. Just cracking it loose broke the ceramic. Hence the $100 tool. Hope this helps. Other than that I am very happy with the 4.6. Great power and good mileage. The Explorer passes very quickly. Typically it takes about 11.5 litres/100 km or about 21 mi/gal US at 110KM/hr or just under 70mi/hr. It weighs 5500 lbs and has AWD.

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