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-   -   Backtap for cross threaded spark plug (http://www.hotrodders.com/forum/backtap-cross-threaded-spark-plug-226831.html)

Infinite Monkeys 12-04-2012 07:51 PM

Backtap for cross threaded spark plug
 
Hi,
Just wondering if anyone has any personal experience with using a backtap to fix a cross thread spark plug hole. I have cast iron heads, not aluminum. I'm concerned that it may not work as well on iron, still not a big deal, I can still pull the head, but compression on all other cylinders is good, so I'm assuming compression on this is also good, just the plug threads need attention.
Or should I just pull the head and tap it from the inside out with a regular tap?
Guess I don't need to explain what I'm trying to fix. It wasn't me, I bought it this way.

Here's a link to what I'm referring to:

Un-Oops That Cross Threaded Spark Plug Hole | Toolmonger

Here's a youtube video:

(try and ignore the awful music)

Thanks.

hcompton 12-04-2012 08:37 PM

Thats a cool video but if it really works it would be great lot of four valve heads have hard to reach spark plug threads.

For regular wedge heads i think a regular tap is a better option. But i think pulling the head is best you can never know if you got all good threads or just a few left. Once the heads off you can put in a timesert. If the threads are really bad.

What kind of head is it. Or engine type.

Infinite Monkeys 12-04-2012 09:17 PM

It's a 2 valve, 1993 FI, 460. I'll look into the timecert. don't know about those.
My guess is that it's just the first few threads. I can't even start the plug. However, the plug was in there pretty tight when I removed it, so it's entirely possible there may not be much left.
I think you are right, pulling the head is the right thing to do.
If I do pull the head, can I then tap from the inside out? I haven't done this before.
Thanks

cobalt327 12-05-2012 12:29 AM

Quote:

Originally Posted by Infinite Monkeys (Post 1619187)
It's a 2 valve, 1993 FI, 460. I'll look into the timecert. don't know about those.
My guess is that it's just the first few threads. I can't even start the plug. However, the plug was in there pretty tight when I removed it, so it's entirely possible there may not be much left.
I think you are right, pulling the head is the right thing to do.
If I do pull the head, can I then tap from the inside out? I haven't done this before.
Thanks

Inside out is fine, but I would use a well lubricated thread chaser first to see if it will reform/untweak the threads w/o removing metal. Only if that didn't work would I use a thread cutting tap.

cdminter59 12-05-2012 02:00 AM

Backtap for cross threaded spark plugs
 
Another tool to use is a spark plug thread chaser. Most Auto Parts stores carry them. Craftsman Spark Plug Hole Thread Chaser - Tools - Mechanics & Auto Tools - Automotive Specialty Tools. I think 14mm is your spark plug thread size. Take an air hose and blow all around the spark plug hole to clean the area. Put a little dab of axle grease on the thread chaser to keep metal and dirt out of the cylinder. Use a shop vac to suck anything out of the hole when done.

cobalt327 12-05-2012 02:20 AM

If that tool is anything like the Lisle tool I have (they both look identical- like the same photo! Photo below is from a Lisle ad), be sure to dress the ends of the threads where the flutes cut across them (arrows below) if there's any raggedness to them. Hopefully the tool you get doesn't need anything, but do check it first.

http://www.hotrodders.com/gallery/da...lug_chaser.jpg

Infinite Monkeys 12-05-2012 05:44 AM

Can the chaser be used from the outside.

If not I'll pull the head and first try chasing then the cutter from the inside.

Thanks guys.
Much appreciated.

hcompton 12-05-2012 05:55 AM

Here is a site that sells time serts not sure if they price or site is any good just pictures to ref.

+ TIME-SERTŪ SPARK PLUG THREAD REPAIR KITS + spark plug stripped thread repair kits for spark plug problems, thread stripped spark plug repairs in damaged threads in spark plug hole stripped out approved thread repair, aluminum head spark plug repair

++ TIME-SERT SPARKPLUG Standard Repair ++

These can be done with the head on but i would not. best to get it rigth from the get since its got to last a long time. Use plenty of antiseize on your plugs once complete.

Also if you mess up the time sert the head is trash. So thread chase tap may be better. But you will need to go inside out since the threads will not start on the other side.

Never ever use a heli coil to fix bad threads if a time sert will do the Job these never come out and get screwed up they are usally better than the original threads. Heli coils will crap out the first time the plug is removed usally.

cobalt327 12-05-2012 10:34 AM

Quote:

Originally Posted by Infinite Monkeys (Post 1619286)
Can the chaser be used from the outside.

If not I'll pull the head and first try chasing then the cutter from the inside.

Thanks guys.
Much appreciated.

First, the best way to do this w/the head on is w/the internal chaser, as you know.

The cheaper chasers can be used from the outside. The threads of the chaser should be slightly tapered to allow it to start even w/buggered threads. The rubber O-ring is there to hold the chaser in a socket w/o falling out. If you're going to go in from the outside, the tapered threads are important because you generally only get one shot at it- either it'll work or it'll cross thread, and if you use a chaser w/an abrupt start to the threads (see below), starting the tool w/o cross threading is hard. If you're careful you can add the taper yourself.

You might find the double ended chasers are too bulky. I have a long single thread chaser here but I cannot seem to find it online. There are single ended thread chasers (like K-D p/n 3379) that can be used w/a 3/8" extension and ratchet or a 5/8" plug socket. It is shown below.

Good luck.

http://www.denlorstools.com/shop/ima...ad_Tool_LG.jpg

hcompton 12-05-2012 10:42 AM

Quote:

Originally Posted by cobalt327 (Post 1619371)
First, the best way to do this w/the head on is w/the internal chaser, as you know.

The cheaper chasers can be used from the outside. The threads of the chaser should be tapered to allow it to start even w/buggered threads. The rubber O-ring is there to hold the chaser in a socket w/o falling out. If you're going to go in from the outside, the tapered threads are important because you generally only get one shot at it- either it'll work or it'll cross thread, and if you use a chaser w/an abrupt start to the threads (see below), starting the tool w/o cross threading is hard. If you're careful you can add the taper yourself.

You might find the double ended chasers are too bulky. I have a long single thread chaser here but I cannot seem to find it online. There are single ended thread chasers (like K-D p/n 3379) that can be used w/a 3/8" extension and ratchet or a 5/8" plug socket. It is shown below w/the abrupt threads.

Good luck.

http://www.denlorstools.com/shop/ima...ad_Tool_LG.jpg

Right words there are if you start the thread chaser wrong you will trash the threads. This is the reason that the head needs to come off so you can start the tap properly from the back side. You can force any tap down the hole and hope it hits the right spot but its going to cross and mess up the head. i would run the plug in from the back side and see if it cleans things up a little first.

cobalt327 12-05-2012 10:47 AM

The threads in a cast iron head will be trashed if someone is stupid enough to continue to thread the chaser in even though it is taking too much torque. Most guys will have sense enough to stop as soon as they feel any undue resistance. At that point, the other options should be explored.

The internal chaser is used from the inside out, w/the head on the engine.

cobalt327 12-05-2012 11:25 AM

Infinite Monkeys, if you end up pulling the head, look closely at the threads at the end (chamber side) of the plug hole. These threads at the very end are often folded over or otherwise in poor shape and might be filled w/carbon, and will need to be cleaned and/or dressed. This is yet another reason to use a tapered chaser/tap.

You can do a reasonably good job of cleaning the threads even on an assembled engine by chucking a brass 12 gauge shotgun bristle brush into a drill. Spin the brush in the hole using carb spray to clean the threads.

Infinite Monkeys 12-05-2012 05:07 PM

First, I want to say thank you for all the advise. Because of help from people like you, I have tackled projects I would never have and always succeeded !!!!!
I just bought a single sided, taped chaser, the kind you use a 3/8" rachet on and will be pulling the head to do all the work. I will also replace the valve seals and reseat the valves.
My plan is to first try chasing it, if that does not work, I'll tap it and lastly put in a time cert. I will chase and tap from the inside. To me it's not worth destroying a head for a days work.
Again,
Thank you.

hcompton 12-05-2012 06:08 PM

Quote:

Originally Posted by Infinite Monkeys (Post 1619538)
First, I want to say thank you for all the advise. Because of help from people like you, I have tackled projects I would never have and always succeeded !!!!!
I just bought a single sided, taped chaser, the kind you use a 3/8" rachet on and will be pulling the head to do all the work. I will also replace the valve seals and reseat the valves.
My plan is to first try chasing it, if that does not work, I'll tap it and lastly put in a time cert. I will chase and tap from the inside. To me it's not worth destroying a head for a days work.
Again,
Thank you.

Excelent plan you will succeed for sure just take your time and it always works out in the end. Be sure to check all the threads while your threads while you got the head off.

@cobolt i am not suggesting your idea was not workable just not as easy to pull off. Tools and advice were good just not as safe as pulling the head. In truth a dealer mechanic that strips a plug would do what you said and if that didnt work would drill and timesert the head without ever telling the customer. Or careing if some small shards got into the head. As long as ot does blow up before it leaves the shop. Sad but true a mech working flat rate does not get paid to pull a head to fix threads and even if he was paid he would not since the short cut pays the same money. These are the advantages we get by working on our cars ourselves. We get to make these choices.


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