Removing sheared spark plug?
 

One of our desert-bashing Dominos delivery bikes (a Honda Innova 125) has a bit of a problem. On attempting to remove the spark plug the plug sheared in half, right down at the start of the thread.

Does anyone have a genius idea for removing this - we have tried a stud extractor, it's just milling bits of plug out. We have also tried a load of penetrating fluid and heat to get it moving, and a copious amount of swearing which seemed to have no affect at all.....

sheared plug
 

When verbals fail, then science has to take over.
My experience is to take the top off, make a tool to fit the electrode, maybe a bit of pipe with a slot in it, attach a long lever, and back it out. You will not get many chances, so go slow and powerfull.
If this fails you will have to mill it out using specialist equipment, any machinest workshop will bill you for an hour, and they pay us well.
Good luck.
Peter, in Oslo

I had the same and ended up taking the head off and drilling the remains out to a diameter marginally less than the plug diameter. I then managed to pick out the thread remains and clean up the head threads with a tap. This was a pain to do and now I think I would just drill it out and fit a helicoil or similar thread insert. Depending on the bike you might be able to do this in place - if you try this heavily grease the drill and taps to try and collect as much swarf as possible. Good luck

Is there enough of the plug left to use some chemical metal to bond a screwdriver to it?

Let the metal set then unscrew.

Use the biggest driver you can and de-grease the area well before you use the chemical metal...

can you post a photo so we can see how much metal is left ?

if you cant start it turning with a small punch and hammer, try milling a slot in whats left with a dremel for the screwdriver and liquid metal trick....anything to give it more purchase.

I've only done this once so cant be sure that it will work every time.

Tools; drill and bits, diameter to suit a junior hacksaw blade, junior hacksaw or a bowed piece of steel to use as the hacksaw frame, bent to suit the shape of the head.

Make sure the head is off. Drill a hole out in small steps until you can easily put the junior hacksaw blade through the hole. Hook up the hacksaw to the hacksaw frame or bowed steel. If you cant do that then try some wire around the blades end hooks to give you a bit more leverage.

Slowly cut through the side of the sparkplug, do another cut opposite. Make sure you only cut the plug and not the head.

If the old plug does not drop out, use a screwdriver to turn the plug out.

Going slowly is paramount so that the thread is not damaged.

Caveman approach.Bash a big torx bit into it and try and wind it out.Don't blame me if the engine gets smashed to pieces though.

Cheers Trophy, have tried that on other bolts, might work?

*easy out* does NOT meant easy out!

Might try collapsing the plug with a hacksaw next, as suggested..... Failing that will try some semtex

chip out the ceramic insulation if there is any, then carefully drill down through it with a drill the core size of the thread. the bits of thread left can be picked out with a scriber

That's what I'd do !!

If the plug sheared off then it's obviously not just "a bit tight"..

It's highly probably that the metals have chemically bonded. I would drill it out as far as I could and pick out the threads...

You maybe looking to get a new thread put in too...

Is this still a problem ?
 

I would like to hear the fix that worked.

mmm, this is still a problem....

As I had a spare engine lying around untested I dropped that in instead, but still need to get this one running so we have a race spare - although I reckon these little Hondas will do great - we've done four long full-throttle runs on them now without any sign of complaint - they'll even touch 70 fully loaded with camping kit and homebrew! (with the right hill)

If the ceramic centre of the plug has been smashed out, a rawlbolt slid inside and tightened could possibly be used to turn out the thread - maybe!

Head on or off ?
 

Can you post a picture of the offending hole :cool4:

If the head is still on then I would do something along the lines others have suggested and glue a big screw driver in there first and see if you can unscrew it. But having said that seeing as the plug sheared off I doubt it will be compliant. Perhaps you could find a small piece of tube with a cut down one side that could be inserted and then expanded via a screwdriver in the slot to try and turn the plug left overs out ?

If the head is off then I would try being very careful with a dremel and cut a slot in one side to try and collapse the plug. If one cut doesn't do it then 2 will. Of course a junior hacksaw would be quicker..

Am now restricted to sofa-based repairs having just broken my ankle so will crack on with the stuck plug tomorrow!