Topic: spark plug hole tap

[frostypuck]

Does anyone have any info they can point me to regarding a "reverse tap" that cuts the sparkplug hole threads on the way out as opposed to as you turn it in? I have a sparkplug that corroded to the head, and when I tried to remove it, it snapped off flush with the outside. An easy-out didn't work. I'm thinking that the side walls of the remaining plug bit aren't that thick, and I could tap the hole and thus eat up the old plug and get new threads at the same time. This info isn't strictly for an sohc4, but if the technology is out there it would be worth sharing with everyone.
Thanks,
Chris in Boston

[Terry in Australia]

G'Day Chris, Hmmnnnnnn, that sounds nasty, so only the threaded portion of the plug is left in the head? Have you tried soaking/heating it as well as that "easy out" treatment? I would have thought you could be quite savage and bash one of those wedge shaped tools into the remains of the plug without damaging the threads?

I've got a 14mm spark plug "helicoil" kit for my Suzuki GS1000 engine which works quite well, but I don't know of a kit that works in reverse, because obviously you've gotta thread it in to thread it out? if you can access the hole with a drill bit, you might need to utilise the small-bigger-biggest method to carefully drill out the spark plug remains, and when you've only got the actual whispy threads left, carefully pick them out with a metal scriber.

I did this with the broken off exhaust studs and didn't need to helicoil them, just ran the tap through to clean them up, and now I use an anti-sieze compound to stop them freezing in place, via electrolysis. Cheers, Terry.

[Clyde]

The spark plug and hence tap size is 12mm by 1.25mm pitch
Good Luck
Clyde

[cb(r)]

this "reverse tap"  idea would be news to me.  just practice patience  with a good oil like kroil or even wd-40 etc.  If you do not have anything left to grip on of the plug you might want to consider a left handed tap that is smaller  than the actual plug, hole.  inert   a left handed bolt to try and turn out the remaining plug.  there is a possibilty the threads were cross threaded or damaged to begin with thus the helicoil idea is looking pretty good.

[frostypuck]

It appears that all of the plugs are corroded into place. When I begin removing them, the threaded portion remains and everytrhing else snaps off. I'll try the left-handed tap idea. Also, would it be possible to use positive pressure to my advantage? Such as hooking up a blwer to the exhaust pipe and turning the engine til the exhaust valve on the affected cylinder is open?
Chris in Boston

[Bodi]

Sounds like your problem is first how to get the plugs out and second how to get out whatever crap goes into the cylinder while getting the plugs out. The worst stuff will be any ceramic bits I think, they would abrade the cylinders badly.
I would get out my propane torch and heat the plug remains and head up, pretty damned hot but not glowing or anything. Then pour some penetrating oil - normal brake fluid works pretty well - in there and let it sit. The fluid will get sucked into the threads as the thing cools down.
Hopefully the engine is out of the frame, getting at 2 & 3 will be about impossible otherwise. Whatever heroic efforts are required, you want to get those plugs out if there. A large easy-out should work if you can drill a big enough hole through the plug; there's a risk that the drill will catch and turn the plug stub through the hole and into the engine - that would be a right bastard to get out! You will probably need to punch the ceramic stuff into the cylinder before drilling as it is very hard and a normal drill will just go dull trying to cut it.
All in all I'd recommend removing the head and working on it separately. The job itself will be easier and you won't have to worry about detritus in the cylinders.

[frostypuck]

Actually all the hard work is done, all the ceramic bits came out in one piece, with the rest of the plug. ALL that's left is the threaded part and of course the grounding part of the electrode. There is currently an easy out jammed in one of the busted plugs, which won't move left nor right, and won't back out the threaded part.
Blah.
Chris in Boston

[frostypuck]

I think I found the item that taps the hole from the inside-out. Bit pricey at $50+ but...
http://www.toolgiant.com/t/Taps/KD_Back_Tap_14mm_Internal_Spark_Plug_Rethread_Tool_B00063YDKE.htm
If the link doesn't work, it's called a "Back-Tap" by K-D tools.  We'll see.
Chris in Boston

[Dennis]

.......... Bit pricey at $50+ but...

 

But it's not the right size. Do they make one in the size you need?

[kaysystems]

Here's one on eBay.....wrong size again, but he used to have 12mm ones

http://cgi.ebay.com/KD-Tools-10mm-Spark-Plug-Re-Thread-Tool_W0QQitemZ4417114380QQcategoryZ20764QQrdZ1QQcmdZViewItem

David

[Dennis]

So it must be available in 12 MM. Of course the remaining section of sparkplug must be removed first.
At his prices however, I would go to my favorite local auto parts store and have them order it.

[hymodyne]

I made a thread chaser out of a long hex head bold of the proper metric diameter and thread pitch. I took a stone grinding wheel to the first dozen threads or so at three different places, laying grooves around the diameter of the bolt; poor man's thread chaser. might save you some $$ after you get the plugs out.

hym

[Bodi]

If you can get the plugs out, the normal way to chase spark plug threads is to coat a (standard) tap liberally with chassis grease. The shavings etc. stick in the grease and don't go in the engine.

[Dragman836]

remember that aluminium expands and cools at a diffrent rate then does the steel part of the spark plugs,therefore I would heat the easyout then spray it with PB Blaster then let everything cool to room temp ,then reheat it back up spray it again then go at it and if it dont come out then repeat. Also if you know your going to change the plugs and dont want to use anti sieze on them then as soon as your done riding while the engine is hot and expanded more than steel break em loose then

[Terry in Australia]

That's an interesting tool Chris, how about you buy it and when you're done with it, I buy it from you for half price? I don't have any bad threads in any of my heads, but what the hey, I could bugger one tomorrow? Ha ha, Cheers, Terry.

[frostypuck]

Just to update my question...I've picked up the appropriate tap and drill bit, and this weekend, I'm going to attempt to un-screw-up this head. As I said in the first posting, this isn't strictly sohc4 related, in fact the head in question is in a truck, and since it has an iron head and large cylinders, I'm going to fill the cylinder with shaving cream prior to drilling/ tapping so that when all's done, hopefully one or two turns of the motor should eject any chips. And any remaining bits may come out with a magnet, which of course would be impossible in an sohc head. P.S. does anyone know what is the prevailing metal that spark plugs are made out of? Is it magnetic?
Thanks for all the suggestions. If it goes well, I'll post my results.
Later,
Chris in Boston

[dusterdude]

the body part is steel of some sort

[tino montreal]

Isn't the thread size 12mm 1.5?

[Terry in Australia]

How'd you find this thread Tino? It's over 8 years old! 

[tino montreal]

I searched....having problems with threading for plugs. In any case found that they are 12mm 1.25 but searching for length of threads.
Thanks

[martin99]

I doubt very much if the plug thread protrudes into the combustion chamber so you could just measure a plug. Or remove a plug and poke a thin wire down the hole, 'feel' for the end of the thread (probably see it with a torch), mark the wire where the plug seats and then take your measurement.

[tino montreal]

Good point. Will do. I see some 15mm long, 18mm and some 24 mm long.
Thanks.