How To Fix Stubborn (possibly crossthreaded) Sparkplug?

[DarkDevil]

I cannot seem to get a new plug into #2. I replaced them this morning and All went in fine except for #2. It won't catch on at all. Using a flashlight I noticed a "blemish" over 2 rows, about 1-1.5mm long. But, its about 3 rows of thread in. So it shouldn't effect it from getting in, in the first place. So.. What Can i Do?

If i want to lube it, should I WD40 it? and should i be worried about anything getting into the plug hole?

If it is crossthreaded what can i do? Can i pick up a tap that fits in and retap the hole? If i did this, would i have to take the engine off so avoid metal bits from getting into the engine?

[Macmatic]

Hi DarkDevil,

Did you check the threads on the plug itself? I've seen one or two that were messed up right out of the box with no real "first thread". If the plug is okay you might have to tap or helicoil the hole.

If you think its just the first thread or two you could try running a tap in very lightly just to clean up those first couple. I'd make sure the valves were both closed and then stick a thin air nozzle inside the cylinder and blow it out really well. This should get any small shavings back out the plug hole if you pulse it and move the nozzle around. Use goggles or eye protection when you do this...trust me.

Someone posted a link to a product called the "Back Tap" not long ago and it looks pretty interesting. It inserts into the hole and then expands to the proper size letting you use the good threads at the bottom of the hole as a guide for the tap. www.starrproducts.com

Good luck!
/\/\ac

[Guy]

Get a thread chaser and run it in and out a couple of times to restore the threads and you should be ok. If there's too much damage and the threads are stripped you'll have to helicoil it. It's not too difficult a job and if you're careful you can do it without disturbing the head. It's not something to be rushed.

[focus frenzy]

if you try to chase the threads with a tap, grease up the tap to catch the fragments of metal and keep them from getting in the engine, clean and regrease constantly!
my bike actualy blew the plug and threads out (#3 plug) I used a thread sert. it is a threaded steel insert that comes with a combo reamer and tap that both drills the hole larger and cuts threads for the insert.
once you have the plug hole reamed and threaded (grease up the reamer good!) you use a good brake cleaner to clean the hole and then screw the insert on the plug, you them put a couple drops of high heat permanent lock tite (included in kit) on the outside of the insert and screw it in.

the insert has a ridge on it to prevent it from going in to far, you also need to make sure that the piston is on the compression stroke and the valves are closed as the reamer/tap can hit the intake valve if it is open.

[Jethro]

the insert has a ridge on it to prevent it from going in to far, you also need to make sure that the piston is on the compression stroke and the valves are closed as the reamer/tap can hit the intake valve if it is open.

So you didn't remove the head for the heli-insert either?

[DaveDanger]

If you suspect that the plug threads themselves may be damaged or not cut quite perfectly, set that plug aside and try one of your other plugs that you've already threaded into another cylinder. That will for one thing tell you if the problem is the plug or the head.

You can make a simple thread chaser from an old plug pretty easily, assuming you have access to a dremel type tool or know someone that does. Clamp the old plug horizontally into a vise with the threads exposed. Take a dremel with as large a cutting wheel as will fit, and cut a groove through the threads of the plug from the tip of the plug (near the electrodes) to the other end of the threads, not very deep, but to the bottom of the thread. Rotate the plug and do this a total of about 5 or 6 times. What you'll end up with is a plug that resembles a thread tap. Clean up the threads with a good wire brush and you'll find that it does a superb job of cleaning crud from cylinder head threads, and will very easily polish out tiny nicks and imperfections from the existing threads.

Remember to NEVER attempt to start a spark plug in any head material with anything but your fingers or a rubber hose slipped over the small end of the plug. Using your fingers or a piece of hose only, it's almost impossible to cross-thread a plug. If you begin with a socket and extension or ratchet, it's very easy to cross-thread or damage the threads and not even know it till it binds and quits turning completely. Especially in an aluminum head without factory heli-coils.

[focus frenzy]

the insert has a ridge on it to prevent it from going in to far, you also need to make sure that the piston is on the compression stroke and the valves are closed as the reamer/tap can hit the intake valve if it is open.

So you didn't remove the head for the heli-insert either?

nope, I used molly assembly grease and filled the groves in the tap and would do one or two turns them back it out and clean out the cuttings and re-grease, then back in.

didnt get one itty bit of aluminum in the cylinder!

the threadsert is solid, not coiled like helicoils are.

[DarkDevil]

I tried a sparkplug from another cylinder, one i had installed at the same time i attempted the stuck one, and it didn't work. I also tried reinserting the one that had been in there up until now but it didn't work.

I'll try making my own thread chaser using an old sparkplug. Failing that I'll venture out to price a thread chaser/tap. Anyone know how much these are? That product that does the reverse chase is 50 bucks american. I'm up in canada, so i'd guess after tax and conversion it'd cost me near 80.

How do I make sure the valve/head is in the closed position?


edit: I assume i need a 12mm thread chaser?

[Macmatic]

How do I make sure the valve/head is in the closed position?


edit: I assume i need a 12mm thread chaser?

I'm pretty sure you need a 12mm yes. Someone correct me on that if I'm wrong?

For both valves to be closed the piston needs to be at top dead center on the compression stroke but I'm not sure how you'd tell if it was on the compression stroke or not with the valve cover on.

That back tap is pricey but if you need it once its still cheaper than pulling the head.

/\/\ac

[JRiveraS]

I have the same problem. I put some heat sylicone on the plug and screwed it as far as it went. Then I posted the question here and someone gave me this site...

http://www.starrproducts.com/newBT.htm

The bike is working fine with the sylicon fix but I know that as soon as I replace the plug I have to fix the thread. Doing it from above may just continue the double thread thinning the existing threads. That, eventually, will result on the engine spitting the plug out.
While you have good threads in the bottom it sounds good to begin from bellow. With this gadget, there is logic. Maybe, just maybe, you are able to rethread the socket the right way and the only thin threads will be at the top. Be careful everytime you put your plugs in, the crossthread may reopen.
Good luck, if you do try it, let me know. Maybe I haven't tried it before and learn from your mistakes, lol

jrs

[DaveDanger]

To make sure the valves are closed and the piston is up... remove all your plugs for ease of rotation. With your fingertip over the plug hole of the cylinder you are working with, bump the starter (or nudge the kickstart) until you feel air pressure building against your finger. At this point you need to be able to turn the crank pretty slowly, so unless you do have a kickstarter, remove the cover at the right-hand end of the crank and carefully and gently rotate the crank using the bolt exposed. Poke a drinking straw into the plug hole and allow it to rest against the top of the piston. Continue to rotate the crank in the forward direction until the straw stops it's outward (upward) movement. The piston should now be at top dead center... give or take a degree or so, and the valves should both be closed.

[focus frenzy]

you can look down the plug hole and see the intake valve.
if you can see piston crown but not the edge of the valve, it is closed.

[DarkDevil]

unless you do have a kickstarter, remove the cover at the right-hand end of the crank and carefully and gently rotate the crank using the bolt exposed.

I'd rather not have to pull the cover. What if I put it in gear and moved the rear wheel? Does this turn the crackshaft?

[DaveDanger]

That'd work, just not as precise. But heck, for what you're doing... it hasn't gotta be perfect.

[Flying Merkel]

if you try to chase the threads with a tap, grease up the tap to catch the fragments of metal and keep them from getting in the engine, clean and regrease constantly!................


..............the insert has a ridge on it to prevent it from going in to far, you also need to make sure that the piston is on the compression stroke and the valves are closed as the reamer/tap can hit the intake valve if it is open.

I had a stripped thread on my GS1000. I had a sparkplug tap. CAREFULLY insert it into the stripped hole! I used the above method, backing the tap out every 1/2 turn and cleaning the theads. 10,000 miles, no problems