How do i repair a cross threaded spark plug hole....

[THE BLACK MAMBA]

I`ve cross threaded my #3 spark plug hole on my aluminum head, so how do i repair it? The head is off the car and i notice only a few threads are cross threaded just on the top...so how do i repair it correctly without damaging the head?

 

[HUMBLE-U2]

helicoil sould work. or pull the head and retap it.

 

[earlbrown]

screw a long spark plug in from the bottom and hit it with a hammer. Then screw the plug in from the top side and torque it down. That should straighten out the threads enough to be back to normal.

 

[pacecarta]

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[THE BLACK MAMBA]

What size tap do i need?

 

[earlbrown]

use a spark plug. a tap with remove metal. Your goal is to but existing metal back where it goes.

 

[Chuck Leeper]

I`ve cross threaded my #3 spark plug hole on my aluminum head, so how do i repair it? The head is off the car and i notice only a few threads are cross threaded just on the top...so how do i repair it correctly without damaging the head?

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

 

[whitehot1]

I can't provide any info on how to repair the crossed threads in your aluminum heads but i can tell you how to avoid it from happening again once you get them fixed.

Use a piece of 3/8'' I.D. x 10'' long transmission cooler hose to install the spark plugs with and put anti-seize on the threads. By using the hose if you don't get the spark plug in straight it will just spin on the spark plug and not allow you to apply enough pressure to let it cross thread into the head.

I have owned my aluminum GN1 heads since 2001 and have never left the spark plugs in longer than 3 months without taking them out to check,clean or replace them so i do it very often and have never had a problem with cross threading by using the rubber hose to install them.

 

[pacecarta]

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[pacecarta]

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[whitehot1]

i use an old spark plug boot , it will spin in the boot before it will ever cross thread and it doesnt flop around like a piece of hose

If your hose is flopping around you must be holding it wrong,mine doesn't flop at all. It is something that works and didn't cost me anything extra since it was left over from a cooler installation.

How well does that spark plug boot work on installing #3 spark plug?

 

[TurboTdr3.8]

http://www.sears.com/craftsman-spark-plug-hole-thread-chaser/p-00947321000P

That one has saved my ass a many a time as all I worked on was aluminum headed cars for a living for 36 years .Plus KD makes a tool that uses a larger tap and put a metal insert in the head and screw the plug into the insert .

 

[pacecarta]

#

 

[whitehot1]

#3#6 # 5 no problems even with AC
why , should #3 be difficult ?

old spark plug boots are free too and they fit in the tool box drawer or track bag nicely

No not exactly difficult but #3 takes a few seconds more than the others to install, but could be the KB header tube / dipstick tube in that location or i'm just getting old and not as flexible as i once was,lol. All the other plugs are a straight shot to install. I use a 2 1/2 ' ratchet extension to do the 2,4,6 plugs on the passenger side and that allows me to stand straight up and not have to bend over the fender like on the drivers side. I use the 10'' length of hose for the plugs on my runabout also so it works for both cars but the hose can be made to any length one wants to make it.

 

[turboc87gn]

Whenever i want to thread something in that i could possibly crossthread i turn it the wrong way first by hand youll feel the threads "drop" into place then thread in a few turns by hand ,then put the socket wrench on it.....

 

[turboc87gn]

screw a long spark plug in from the bottom and hit it with a hammer. Then screw the plug in from the top side and torque it down. That should straighten out the threads enough to be back to normal.

What does hitting it with a hammer do? Do you do it after youve screwed the plug all the way past the bad part or tap it as you go through the bad area (like tap,turn a little ,tap turn a little)?

 

[earlbrown]

It straightens up the threads without removing metal. The reason you start from the bottom is because those threads aren't messed up.


That's a pretty common repair when I was in the motorcycle business.

 

[Buick Mark]

Whenever i want to thread something in that i could possibly crossthread i turn it the wrong way first by hand youll feel the threads "drop" into place then thread in a few turns by hand ,then put the socket wrench on it.....

Bingo! I do the same thing

 

[Jerryl]

Here's my $0.02
If the heads are off, start from the chamber side and use a form tap, not a cutting tap. The form tap does not remove material, and work hardens the material.
The process Earl descibes is the one you use of you don't have a form tap.

 

[dartguy340]

screw a long spark plug in from the bottom and hit it with a hammer. Then screw the plug in from the top side and torque it down. That should straighten out the threads enough to be back to normal.

This is the same trick I was gonna recommend, as we did this when rebuilding cylinder heads if the threads weren't too bad. We never hit it with a hammer though after running it in....