Cross threaded spark plug
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Joined: Jan 2016
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From: Reno Nevada
Cross threaded spark plug
Ok, so I have managed to cross thread one spark plug in my 500 mile Brodix heads.. Engine in the car, everything in running order, almost ..
The plug was not forced in at all, but I have tried and tried for about 6 hours to get a plug in the hole not cross threaded and I just cant seem to do it. The threads do not appear to be damaged from what I can see with them in the car, but they are obviously slightly damaged or at least not a clean thread cut on the outside portion of the hole.
The hole does not need a helicoil or anything quite that major, but I have put some effort into getting a plug in the hole and still it is sitting empty.
My next approach may have to be to pull the head and run a tap from the back of the hole to clean it up, but obviously this is not an ideal solution from where I am sitting now.
Wondering if someone out there has some magic idea of getting a plug into the hole without pulling a head from my BBC with the motor in the car. And of course the heads are put in with studs, making it extra special to remove a head from inside the engine compartment of a vette.
Thanks
The plug was not forced in at all, but I have tried and tried for about 6 hours to get a plug in the hole not cross threaded and I just cant seem to do it. The threads do not appear to be damaged from what I can see with them in the car, but they are obviously slightly damaged or at least not a clean thread cut on the outside portion of the hole.
The hole does not need a helicoil or anything quite that major, but I have put some effort into getting a plug in the hole and still it is sitting empty.
My next approach may have to be to pull the head and run a tap from the back of the hole to clean it up, but obviously this is not an ideal solution from where I am sitting now.
Wondering if someone out there has some magic idea of getting a plug into the hole without pulling a head from my BBC with the motor in the car. And of course the heads are put in with studs, making it extra special to remove a head from inside the engine compartment of a vette.
Thanks
Race Director
Joined: Mar 2017
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From: Virginia
I've helicoiled aluminum heads while they are still in the car. You just need to watch where the insertion tang goes, but it is magnetic.
Have you tried a tap and/or thread chaser yet? That might be all you need.
Have you tried a tap and/or thread chaser yet? That might be all you need.
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Joined: Jan 2016
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From: Reno Nevada
Maybe I can go look at McMaster Carr to see what sort of thread chasers they may have.
The plug looks very square from where I am looking, but then that is through a mirror to see the plug/head interface.
This is number 5 hole, under the the brake master cylinder for viewing. Could be number 7, so there is that....
The plug goes in about one rotation and then is clearly cross threaded. Have stopped after that.
Race Director
Joined: Mar 2017
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From: Virginia
Do you have your exhaust manifolds/headers off already?
Perhaps you can get a photo with your phone (you may need 3 hands to do this). Please post it if you do!
If you have a borescope, or a friend that does? That might also show what is going on.
Perhaps you can get a photo with your phone (you may need 3 hands to do this). Please post it if you do!
If you have a borescope, or a friend that does? That might also show what is going on.
Thread Starter
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Joined: Jan 2016
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From: Reno Nevada
I had thought about the borescope, but have not purchased one. Perhaps a cheap one is in my future.
Was thinking of making a jig for a tap or even the old spark plug with socket to be held on the head to ensure the plug/tap is straight. I have a chunk of aluminum and a lathe that I can probably make work. Not sure how I may hold it on the head, might just be double sided tape or even loctite to temporary hold it in place while starting a tap.
Headers are still on the heads. Maximum accessibility.
Was thinking of making a jig for a tap or even the old spark plug with socket to be held on the head to ensure the plug/tap is straight. I have a chunk of aluminum and a lathe that I can probably make work. Not sure how I may hold it on the head, might just be double sided tape or even loctite to temporary hold it in place while starting a tap.
Headers are still on the heads. Maximum accessibility.
Melting Slicks
Joined: Dec 2009
Posts: 3,224
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From: Thunder Bay
I had thought about the borescope, but have not purchased one. Perhaps a cheap one is in my future.
Was thinking of making a jig for a tap or even the old spark plug with socket to be held on the head to ensure the plug/tap is straight. I have a chunk of aluminum and a lathe that I can probably make work. Not sure how I may hold it on the head, might just be double sided tape or even loctite to temporary hold it in place while starting a tap.
Headers are still on the heads. Maximum accessibility.
Was thinking of making a jig for a tap or even the old spark plug with socket to be held on the head to ensure the plug/tap is straight. I have a chunk of aluminum and a lathe that I can probably make work. Not sure how I may hold it on the head, might just be double sided tape or even loctite to temporary hold it in place while starting a tap.
Headers are still on the heads. Maximum accessibility.
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
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He ou tried one of the other plugs to eliminate the plug as the issue. If you have a thread gauge you could take the proper gauge and put it in there and twist it along the threads to see if you can feel any irregularities before using a chase
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Thread Starter
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Joined: Jan 2016
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From: Reno Nevada
Thanks everyone for the thoughts, after the holiday, will probably make a jig to keep my tap square and then run a tap up the hole. Trying not to have to pull the head or worse damage the threads.
@drwet Good info on the cheap borescope. thank you.
@drwet Good info on the cheap borescope. thank you.
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Joined: Mar 2016
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From: Napa Valley California
It sounds like there is just a burr on the thread.
You can over think and over engineer this to the point you cause your own catastrophe.
First remove the exhaust header.
Estimate how deep the tap will go into the head so the tip of the tap doesn’t go all the way into the combustion chamber, then mark the tap and don’t go into the hole any deeper than your mark.
Take a tap with some good quality “aluminum tapping fluid” and run the tap into the hole using your fingers only.
Go in an eighth turn and out a quarter of a turn using slight finger tip pressure turning the tap.
Constantly remove the tap and clean it with a steel brush and tapping fluid.
Once you get to the burr go in and out really easy until you clean the thread.
If you get to the point you can’t turn the tap using your fingers only, stop, remove the head and do it on the bench.
You can over think and over engineer this to the point you cause your own catastrophe.
First remove the exhaust header.
Estimate how deep the tap will go into the head so the tip of the tap doesn’t go all the way into the combustion chamber, then mark the tap and don’t go into the hole any deeper than your mark.
Take a tap with some good quality “aluminum tapping fluid” and run the tap into the hole using your fingers only.
Go in an eighth turn and out a quarter of a turn using slight finger tip pressure turning the tap.
Constantly remove the tap and clean it with a steel brush and tapping fluid.
Once you get to the burr go in and out really easy until you clean the thread.
If you get to the point you can’t turn the tap using your fingers only, stop, remove the head and do it on the bench.
Melting Slicks
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From: Dallas TX
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Burning Brakes
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From: Fort Wayne IN
Bring the piston up with the valves closed, stuff cotton rope into the combustion chamber, run your thread chaser in, shop vac the hole good, pull the rope out and any bits you missed will come out too.
Dr. Detroit
Joined: Mar 2012
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From: New Braunfels Texas
If you're using a tap, glob some grease on the tap to hold the chips.
They also make thread chasers for spark plugs: https://www.amazon.com/ARES-Limited-...ps%2C76&sr=8-5
Just a couple ideas...
They also make thread chasers for spark plugs: https://www.amazon.com/ARES-Limited-...ps%2C76&sr=8-5
Just a couple ideas...
Jebby
Is my vette stock?? HAHA
Joined: Oct 2015
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From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
Race Director
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From: Virginia
Melting Slicks
Joined: Nov 2010
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From: Michigan
I have had brand new out of the box heads with slight thread issues. Just use a spark plug thread chaser should be able to get one at a local parts store, I got one at Ace Hardware. I wouldn't recommend a sharp tap, may do more harm than good. Just take your time and oil the chaser, if it gets stuck don't force it, work n back n forth.
Wouldn't bother pulling the head, I've used a time-sert plug repair kit to fix an alum head on engine. Just drilled n tapped, fine alum will not do much if anything, Aluminum will burn. Drove that car for another 40k before I scrapped it.
Wouldn't bother pulling the head, I've used a time-sert plug repair kit to fix an alum head on engine. Just drilled n tapped, fine alum will not do much if anything, Aluminum will burn. Drove that car for another 40k before I scrapped it.