Stripped Spark Plug Threads - Recommendations?

[Mark in PDX]

My #1 cylinder spark plug is stripped. That is what I get for changing out the bosh spark plugs the previous owner put in this and putting in Motorcraft... They obviously messed up the threads as they came out with the bosh and the Motorcraft wouldn't tighten down.
Sigh.

So- I have seen a couple threads that mention helicoiling it.. And I have done that with my other cars on the valve cover threads.

My question is, does anyone know specific parts/kits I should use, recommendations for the best tool?
I have never done a spark plug and this engine only has 100k on it, so I REALLY don't want to screw this engine up with metal shavings in the cylinder, but am not sure I have the time/capability to yank the head at this point.
I don't have a place where I can do it safely, not really. So I'd like to try to repair in car.

Suggestions?
Mark

 

[yamahaSHO]

If it is stripped, about the only thing you can do is pull the head. You sould try to do it in the car and use a vacuum to suck out the shavings, but I wouldn't trust it. You also want to make sure the threads are straight so the plug will seat properly.

Basically, I don't see any way around pulling the head.

BTW, if the other plugs were the right thread pitch, I highly doubt it was the fault of the non-OEM plug that stripped it. Other errors "unknown' had to have caused it.

 

[Mark in PDX]

Well, I know the Bosch plugs didn't do it.. I >assume< that the previous mechanic did what they do on the valve covers and just 'tightened' it and over-tightened it and damaged them, and when I took the plugs out, the threads came with.

I am really really hoping I don't have to pull the head. If it was the front head, I would worry less, but the back head is just a nightmare and I don't have the time to do it right now, and really can't afford to pay some shop 10hrs labor to R&R it for me.

so if there are OTHER suggestions, I am all ears.. If it really gets down to pulling the head, I'll have to park the car til some future date that I would have time to do it, and that sucks since I >just< bought the car to be my daily driver.
sigh
Mark

 

[Off Road SHO]

Mark,

You need to find a "real" mechanic. Helicoils have been used thousands of times to fix your problem without removing the head. A real mechanic will know how to do it without getting any filings in the chamber. Like bringing that cylinder up to the intake stroke (intake valves open) and then pressurizing the intake tract with compressed air while he's doing the drilling and threading. The air flow overcomes any effect that gravity might have used to drop bits of aluminum into your cylinder.

This nation is full of half assed mechanics that can only think as far as their AllData CD collection. (sigh)

If you're going to attempt it yourself, be mindfull of what Jason said about drilling perpendicular to the sparkplugs sealing surface.

Good luck in whichever path you choose.

Tom

 

[93rev2sev]

If nothing else, it's a good excuse for rebuilt heads. If you decide to take the head off, might as well replace both...you will have to buy(most likely, anyway) both head gaskets and all the upper gaskets anyway.

Get some good used heads and have them cleaned up with new valve stem seals and have the valve seats touched up.

Install them, shim them, and never worry about them again.

Of course, that's likely a $600 proposition...whereas, it might cost $150 to have someone attempt to rethread the head while it's still on there...

Neither of those ideas looks like fun, I'm sure...

 

[RAYJAY]

here is a few links to look at with a right Helicoil kit theres no drilling

http://www.popularmechanics.com/automotive/how_to/4212608.html

Start by threading the special Helicoil tap into the remaining threads in the head. This is to ensure the new threads are concentric and parallel with the originals. Continue threading the tap in to cut the new, oversize threads. To avoid getting aluminum chips in the cylinder when retapping the threads, you should coat the tap with grease. The chips will stick to the grease and come back out with the tap. Back out the chip-laden tap, and clean up any remaining chips.

I've also filled the cylinder (before tapping the hole) with oil-soaked clothesline to catch any chips — but that was in a racing engine with a squish band only a few thousandths of an inch deep. Street engines with a more normal compression ratio should be fine if you are careful, and blow the chips out with compressed air. Mostly, you don't want any chips to find their way out the exhaust port and wind up in the catalytic converter.

Now you can thread the appropriate-length coil over the installation mandrel. There's a raised flat on the mandrel that will catch on the tang in the coil, allowing you to thread the coil into your new threads. The coil is a little bit bigger than the threads, which will keep it in place when you're finished. The tang will pull the coil into place from the inner end. Once the coil is in place, remove the mandrel.

Now, use a pair of needle-nose pliers to break the tang off. It's prescored to break off cleanly and easily. Do NOT drop the tang into the cylinder! A few aluminum chips will not damage your engine, but a 1/2-in.-long piece of sharp stainless steel wire will tattoo the top of your piston and the combustion chamber before it finally gets out past the exhaust valve.

link for the helicoil spark plug kits (I DON'T KNOW IF THIS IS THE RIGHT KIT DID NOT CHECK OUT THE THREAD SIZE YET)
http://www.globalspec.com/FeaturedP...ark_Plug_Thread_Repair_Kit_14mm_x_125/23773/0


this system even looks good

http://www.timesert.com/html/sparkplug.html

 

[Mark in PDX]

Thanks for the links.. I'll probably try this first...
Mark

 

[SHOZ123]

I was able to repair a stripped spark plug thread with a threading tool that inserts into the cylinder then you expand it to fit the threads and back it out. NAPA has it.

 

[Mark in PDX]

Thanks Paul, I actually have a NAPA near me so will check that out...
Mark

 

[gas it]

I wouldn't worry about metal dropping into the cylinder, it's just aluminum. Put a helicoil in, and party on!

 

[Lightning]

pack, and I mean PACK, the tap with heavy grease. The heavier the better, not only will this help lubricate the threading process, but cuttings will get caught in grease and remain on the tap insde of falling anywhere.

run in with the tap a ways, back it out, clean the grease cuttings out, repack, run in a bit further, back out, clean, repack, carry on like this until complete...

Do it right and nothing will fall in what-so-ever. Done this more than once with great success.

 

[Mark in PDX]

Ok, so now I am going to be a little bit lazy.. Does anyone know the thread size/pattern I should be looking for in the kits, or which manual I can find it in? I am going to try to do this on Saturday and want to go by napa tomorrow/wed to get the kit to try it with.
The biggest thing I am worried about is the TANG on the helicoil... I DO NOT want to loose that down the hole, so any suggestions on a brand of long nose that will handle snapping it off? I haven't had much luck with the tools I normally buy at (don't laugh, I am cheap) Harbor freight.. (ie china direct)...

Dumb question, no flames allowed, but someone had mentioned that there are some permatex hitemp aluminum repair kits out there that >might< work for that... I am not a big 'jb weld/duct tape' kinda guy, but have been impressed in some of the exotic repairs I have seen done in other industries with this stuff... It is obviously far better than it was in the 60/70/80's...
Anyone ever tried to use this stuff to fix the threads?

 

[Lightning]

I've used helicoils lots, not for this job in particular, but VC bolts, thermostat housing bolts, and lots of other non-automotive stuff. Work great, never had a problem with it.

Haven't tried other types of kits.


As for the tang, see if you can use needle nose vice grips.

 

[Mr Anonymous]

Go to NAPA and buy a 14mm spark plug repair kit. It will include a tap, setting tool, and three inserts. Price will be anywhere from $50-$70 depending on the store. Also get a tube of high-temp RTV, and some grease if you don't have any.

I can post more detailed instructions when I get home late tonight, but basically you want to grease up the tap and run the tap in small increments, about 2-3 turns at a time, back it out, clean it off, re-grease and start over. Using this method the only thing that will get into the cylinder is a very fine aluminum dust, the larger filings will stick to the grease.

I've probably done this on a dozen SHO's without a single problem. In fact on the way to this year's convention I did one for Ian at a rest stop on the NY Thruway. It took longer to find a NAPA than it did to actually fix the threads.

EDIT: The other tool that Paul mentions is called a spark plug back-tap. I've also used one, but usually it only works when only a couple of the threads for the plug are futzed up. When there are at least 3-4 good lower threads it can work really well, but it's also a ~$70 tool so it could be an expensive purchase if it doesn't work. If you can get the new plug to bottom out then the back-tap probably won't work.

 

[Sho-N-Go]

I also would like to add that with the Napa kit there is NO tang for the heli-coil. This tool uses a setting tool to stake it to the head. It works very well.