Cross Threaded Spark Plug

[Bengt_Phorqs]

The Lucha' Libre' makeover project is coming along but I ran into a snag yesterday.  I was going to check the compression and removed the NGK plug from the right hand cylinder but my compression tester would not thread more than one or two turns.  Slight concern so I took it out and tried to insert the spark plug back into the hole.  It would not go back in either even with a generous application of lithium grease.  Big concern now.  

Is there anyway to chase the threads without pulling the heads? I don't want to force the plugs back in and run the risk of stripping the threads completely.

[Rob Valdez 79 R65]

If you aren't going to pull thead, use plenty of grease on the tap to try and catch any junk.

If it were me, I would probably pull the head, just to be sure.  Just be careful with the exhaust nut, if you do.

[montmil]

Is there anyway to chase the threads without pulling the heads? I don't want to force the plugs back in and run the risk of stripping the threads completely.

Back in my poor boy undergraduate days, I once drilled out and added helicoil inserts for both sparkle plugs in my Turnip Bonneville... without pulling the heads. Fired 'er up and, with fingers crossed, hoped the metal trash would be blown out the exhaust.

Rode the bike for several more years...  i say, "Chase 'em" with a grease-loaded thread chaser. YMMV  

Monte

[Justin B.]

I concur with Moe and Larry and have done some spark plug holes in cast iron Chevy heads as well as aluminum Mercedes heads.  I had to put in an insert in one of the Mercedes holes, still without removing the head.  Use a nice sticky grease...

[Bengt_Phorqs]

Thanks to all of your suggestions.  I solved the problem with a really neat little tool I picked up from Northern Tool.  It's a 14mm Back Tap made by Powerbuilt, p/n 640811.  They aren't cheap, about $50, but I found a similar unit at a NAPA store for more than $80.  Well worth the expense to me considering I didn't have to pull the heads and unless you really mess up there is no way you'll get any detritus into the cylinder.  You can see a couple of photos on my flickr site, http://www.flickr.com/photos/8703467@N07/

It took me about 20 minutes moving really slowly and taking my time.  It's recommended to not fully extend the back tap but to make several passes.  That, and use a generous amount of grease.

Anyhow, I was able to get the thread chased, run the compression test, 135-140, and re-install the spark plug.  
Thanks again to all!

[Rob Valdez 79 R65]

Good news (and positive results) are always welcome around here!

THANKS FOR THE FOLLOW-UP!

(I can't see your pictures here at work.  Darn firewall!

[Justin B.]

Rob, being in IT you should not use such a flimsy excuse!

I had never heard of a back-tap before, how does it work?  I just have the old Lisle spark plug hole thread chaser.  Anyway, I never really worried too much as the valves and seats are steel so I figured they could take any bit of aluminum that got away from the grease...

[Rob Valdez 79 R65]

Rob, being in IT you should not use such a flimsy excuse!

No one ever taught me hacking.  

For the last two years, I have had Mozilla Firefox installed on my profile on this work station.  Then it quit working last week for some reason.  It is illegal as hell, so I just deleted it.  Now I bring my music in with me (like the old days ).  

The good news, though, I got the help desk guy to enable me to watch DVD's on here!  Which I forgot about until just now.  We did that last week, and I think I've slept 2 or 3 times since then!  lol!

[Justin B.]

Firefox illegal?  Does that mean it's not sanctioned by the Net Nazis?  I use Firefox on the LINUX box out in the shop and Mozilla/Seamonkey in the house on the XP box...

[nhmaf]

Yes, I personally avoid use of Internet Exploder unless I am at some client's offices, where that is all that is allowed.

It is very predictable, both in its functions and in its flaws, which I think make it attractive for alot of IT deployments..

[Bengt_Phorqs]

Justin, it's a pretty clever design.  The tap works from the inside out.  In order to start at the bottom of the thread and work to the outside it must be smaller than the spark plug hole.  The back tap is essentially a hollow rod threaded to 14mm and tapered to clear any interference.  There is a mandrel inside the rod and when retracted expands the threads.  The threads engage from the bottom and when you back it out it cleans, chases, the threads.

[Rob Valdez 79 R65]

Justin, it's a pretty clever design.  The tap works from the inside out.  In order to start at the bottom of the thread and work to the outside it must be smaller than the spark plug hole.  The back tap is essentially a hollow rod threaded to 14mm and tapered to clear any interference.  There is a mandrel inside the rod and when retracted expands the threads.  The threads engage from the bottom and when you back it out it cleans, chases, the threads.

Very good!  Thanks for the description!

[MrRiden]

I just had to google it to get a visual http://www.back-tap.com/ makes it all clear to me now. clever! Now I know its not this type of mandrill

rich
P.S. I.E. is a virus.

[Justin B.]

Schlick!  I'm not gonna tell you what they sell for on e-Bay!  

[Rob Valdez 79 R65]

Their socket adapters are clever, as well!




The thread tool costs $49.95 according to the reviews.
How much do you see them for on ebay, Justin?