Broken sparkplug in head

neevo

neevo

Over 1,000 Posts
Got a head sitting here to replace my damaged one on the 400F. The heads in pretty good nick except some rough valves however I can get them back to new with done gentle work.

One key issue I'm not sure about is with one of the sparkplug threads. A sparkplug has broken off, the only part left is the brass thread ring. I've been drilling it out with larger and larger bits, hoping it would start to unscrew at some stage, but its not moved yet and I'm getting close to the threads now.

Anyone got done advice on how I can get the rest out without buggering up the threads?

I was thinking of getting the Dremel with a grinding stone on it to gently grind back the remaining metal so I can eventually peel out the threads.

Thoughts?
 
You have a tap and die set? You could probably use that to retap the hole the same size/thread as it was and force the old parts out without damaging it. I would just be sure not to crossthread or then you'll be starting all over. I'm not 100% sure it will work or the thread/size pattern to use to do it but someone else on here should know.
 
Mark, I thought about that but was worried I would just retap the threads in the wrong place and bugger it up.

Brad, thanks mate. Will get the Dremel out and grind it carefully back to the edge of the threads and see if I can finesse it out.

Pretty sure I should be able to pull it out like a curl if I can get enough material off.
 
Try heating the head. Aluminum expands more with heat than the steel of the plug remnant. You could safely heat it in a 400 deg oven. Assuming that you are going to be replacing the valve stem seals anyway, go ahead and crank that oven up to it's maximum temperature.

A trick I recently learned was to apply paraffin wax after heating. The heat makes the wax flow between the pieces you are trying to get apart and acts like high temperature penetrating lubricant.

I would hesitate to try using a tap. It would be damn near impossible to get it perfectly in phase with the existing threads. You would most likely just fuck it up.

If you do fuck it up anyway, (not all that unlikely,) use a Timesert to fix it. Absolutely the best thread restoration product available.
http://www.timesert.com/
 
AlphaDogChoppers said:
Try heating the head. Aluminum expands more with heat than the steel of the plug remnant. You could safely heat it in a 400 deg oven. Assuming that you are going to be replacing the valve stem seals anyway, go ahead and crank that oven up to it's maximum temperature.

A trick I recently learned was to apply paraffin wax after heating. The heat makes the wax flow between the pieces you are trying to get apart and acts like high temperature penetrating lubricant.

I would hesitate to try using a tap. It would be damn near impossible to get it perfectly in phase with the existing threads. You would most likely just fuck it up.

If you do fuck it up anyway, (not all that unlikely,) use a Timesert to fix it. Absolutely the best thread restoration product available.
http://www.timesert.com/
Click to expand...

Cheers Alpha, top info!
 
Yeah I guess I've never really had this issue before myself. Bad idea to retap with metal blocking the threads still... Second that on the timeserts though. I have bought a couple bikes in the past, with blowouts, where the PO decided to use the cheaper helicoil type inserts that just look like a spring and those are garbage for this type of application. One bike had been repaired twice, the same way, and by then the hole in the head was far to big for anything and I sold it to a friend who is contemplating welding something in or just buying a new set of jugs for it... If you do the timeserts on the first occurrence your probably doing it for the last time.
 
Yeah timeserts are a great fix. Had to use 2 in my cases after 2 studs snapped off. Fingers crossed I can Dremel the remains of the sparkplug to reveal the threads.
 
since it broke off it is seized and more than likely no amount of heat will loosen it. the only thing to do now that you have already started drilling is continue if you are centered and then peel the last bit of threads as you reach the minor diameter. then run a starting tap into it to clean up any damaged caused. if you are off center than once you get close use your dremel or pencil grinder..using a good quality ice pick works very well to peel the final bit of threads out. for future reference if the plug body is steel you can weld a bolt to it and try to turn it out that way....
and i agree a one piece thread repair insert is better for this application than helicoil style.
good luck, joe@ v cycle
www.joesvcycle.net
 
Thanks Joe. Drilling is unfortunately slightly off center so I will get close enough with a bit and then do the rest with the Dremel. Fingers crossed I can get to that first bit of thread to peel it out.
 
You were drilling from combustion chamber side?
Drill should stay pretty well centered if you bend back ground electrode, cut it off then punch out ceramic
 
crazypj said:
You were drilling from combustion chamber side?
Drill should stay pretty well centered if you bend back ground electrode, cut it off then punch out ceramic
Click to expand...

Both sides actually PJ as the metal thread part was the only bit in there since I bought the head. Was hoping it would start to unwind itself with the drill but no luck.
 
Had another look at the thread today and I'm not convinced it can be saved. Will be drilling it out for a Timesert.
 
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