Spark Plug Question...totally bizarre

[Chuckster]

I have a 1981 Suzuki GS550T with less than 9000 miles. Last night, I went to change the spark plugs. I pulled all four plugs out which were NGK B7ES. When I went to replace them, the base (threaded part) on the plug on the far left (while sitting on the bike) is much larger than the other three. You can notice the difference just looking at the spark plug hole compared to the next one. All four plugs are NGK B7ES, even the one with the larger threaded base. Anybody know what the heck is up with this? I've never seen it before. The dealer also gave me NGK B8ES to replace them with which all have the same size threaded portion.

[SPARKSS]

I have a 1981 Suzuki GS550T with less than 9000 miles. Last night, I went to change the spark plugs. I pulled all four plugs out which were NGK B7ES. When I went to replace them, the base (threaded part) on the plug on the far left (while sitting on the bike) is much larger than the other three. You can notice the difference just looking at the spark plug hole compared to the next one. All four plugs are NGK B7ES, even the one with the larger threaded base. Anybody know what the heck is up with this? I've never seen it before. The dealer also gave me NGK B8ES to replace them with which all have the same size threaded portion.

Hi there Chuck. If you indeed REMOVED 4 B7ES plugs, they were the same size.

If you actually have one hole thats now larger there's a couple of possibilities. First is that you pulled all the aluminum threads (cored out) this one hole and that aluminum thread material is on the one plug. Second (probably more likely) is that this happened in the past and that there was a Helicoil (or similar) thread insert which now has come out with that one plug (check to see if one plug appears to have a odd looking larger thread wound around it's original thread).

If the latter seems to be the case, all "might" not be lost, a properly installed similar type thread insert or one of the other types of replacement "threadsert" type repairs could be still done - at this point you might want to have an experienced engine builder (small, motorcycle or otherwise) do the work. Many times it can be done with the head installed although it's nicer with the head off.

If you're not talking about the actual plug thread hole but merely the base of a plug, I've seen production differences between old stock and new which can make one plug of the same number appear quite different but on close examination the threads, reach, protrustion will be the same even if overall height is slightly different. Hope this helps

[bwringer]

It sounds like the spark plug threads in the head may have been repaired with a thread insert or helicoil. Sometimes this insert comes out with the plug instead of staying in the head.

You might be able to replace the insert if you can figure out exactly which brand it is, or maybe if you're extremely careful you can remove the old insert from the old plug and put it back with some high-temp locking fluid.

[SPARKSS]

Spark Plug Question.....bizarre.....prevention

Just a note to add Chuck regarding prevention of such a problem (initially).
Never remove spark plugs from a hot ALUMINUM head .....Reason is that immediately after shut-down the aluminum cools quicker than the steel, seizing tightly around the steel plug until all temps are stabilized (cool).

Best cold and never force a plug out or in!

[Steve]

Never remove spark plugs from a hot ALUMINUM head .....

Makes it hard to to plug chops, doesn't it? 8-[


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[Dave8338]

Makes it hard to to plug chops, doesn't it? 8-[


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[Chuckster]

Thanks for the information guys. I just looked at the plug again and it does appear there is an outer threaded piece over the original plug. The threads on it are fine as well as the threads in my engine. I hope they are fine in my engine as they appear to be. I actually found out I had a problem when I attempted to screw my compression tester into the hole and it kinda went down easy and had some play in it. So then, I was wondering what the heck had happened, etc. I looked at the hole threads and they appear to be okay. I don't think the tester fit tight enough when I put in down in there to mess the existing threads up. I thought it was threading since it went in so easy until I realized it wasn't tightening up. Is there any way to get the one off the plug I have? Also, where would I get a replacement if I went that route? And finally, how can you secure it next time so it doesn't come out with the plug? By the way, the engine was cold when I did this last night. I've only had the bike several months so this was my first attempt to change the plugs.

[Steve]

You can check at your favorite auto parts store or a good bike supply to see if they have Heli-Coil kits for re-threading spark plug holes. Most of these kits have a tang on the bottom of the coils that you need to break off, which is not something you want to do unless you can be assured that you will not drop that little piece into the cylinder. Best bet would be to take the head off, but there might be a way to avoid that.


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[Chuckster]

You can check at your favorite auto parts store or a good bike supply to see if they have Heli-Coil kits for re-threading spark plug holes. Most of these kits have a tang on the bottom of the coils that you need to break off, which is not something you want to do unless you can be assured that you will not drop that little piece into the cylinder. Best bet would be to take the head off, but there might be a way to avoid that.


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Thanks Steve. Nothings easy is it? All I wanted to do was replace the plugs. It started out simple enough.

[chef1366]

I pulled a heli-coil out of a cam cap bolt. I screwed the heli coil off the bolt a couple of turns and reinserted it into the threads with some heli coil locking compound. I then pulled the bolt out of the threads without removing the heli-coil with it. I let it set up and it held fine.
Just be careful not to break the heli-coil.
Or just get some new heli-coil threads.

[Chuckster]

I pulled a heli-coil out of a cam cap bolt. I screwed the heli coil off the bolt a couple of turns and reinserted it into the threads with some heli coil locking compound. I then pulled the bolt out of the threads without removing the heli-coil with it. I let it set up and it held fine.
Just be careful not to break the heli-coil.
Or just get some new heli-coil threads.

Chef, how did you get the heli coil off the bolt without damaging it? Mine appears to be on my spark plug pretty tight.

Also, how do I figure out what size heli-coil is on it now if I can't get the other one off?

[chef1366]

Size one of the spark plugs that are fine.
or
Someone here knows the size.
I don't.

[Chuckster]

Size one of the spark plugs that are fine.
or
Someone here knows the size.
I don't.

Was the heli-coil already loose on the bolt you mentioned? I was wondering how you got yours off as mine is really on there pretty good.

[chef1366]

Mine came right off. Yours is probably glued together so maybe try some penetrating oil or just get a new one. The hard part of the job is done which is retapping the threads. All you have to do is thread in some new ones.

[Chuckster]

Mine came right off. Yours is probably glued together so maybe try some penetrating oil or just get a new one. The hard part of the job is done which is retapping the threads. All you have to do is thread in some new ones.

Thanks. Good idea. I'll try some PB Blaster tonight and see if that loosens it up.