spark plug rethreading

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  #1  
Old 06-05-05, 06:11 PM
maiden442
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spark plug rethreading

I have a 99 ford f250 v10 and one day while driving heard loud repeated bang under hood. After further inspection found ignition coil(1 per cylinder) laying on the intake. It cracked off and also found spark plug on intake. I figure that when the last owner had it tuned they must have cross threaded the plug as I couldn't put in a new plug. I bought a tap and retapped it and the tap goes in and out by hand easily now but a new plug only seems to grab 1 thread. Have tried 4 different brand plugs and 2 grab the other ones don't. Any ideas before I put an insert in. The plug grabs and when you continue to tighten- it comes out. Ill probably have to take the head off to do this. Not looking forward to this. Its an aluminum head too and its the second from the back, not easy to get to.Allready have the new coil. Any ideas??
 
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Old 06-05-05, 06:57 PM
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It sounds like you are going to need an insert. If done properly they are stronger than the original threads.
 
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Old 06-05-05, 07:23 PM
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Originally Posted by car nut
It sounds like you are going to need an insert. If done properly they are stronger than the original threads.
Sometimes called Heli-coils
They work great
 
  #4  
Old 06-05-05, 07:56 PM
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Aluminum heads huh,,, you need a heli-coil for sure.
 
  #5  
Old 06-06-05, 06:27 AM
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These heads are known for popping the spark plugs. They are designed so only 3-4 threads hold the spark plug. Any galling, cross-threading, or overtorquing will weaken the threads. Plus, the first few spark plug threads get carboned, and the threads take a beating when you remove the spark plugs. It sounds like you're beyond chasing the threads and a helicoil repair is your only choice.
 
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Old 06-06-05, 09:04 AM
maiden442
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So the only way to put in a helicoil is to remove the head? right? I have seen a double tap at the parts store(Auto zone) that starts with the 14mm tap and then follows with a larger tap to put in an insert which comes with it. You then put rtv high temp around the insert and turn it in. Is this the same or different then a helicoil?
 
  #7  
Old 06-06-05, 09:52 AM
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It can be done with the head in place. The trick is to pack the tap flutes with grease to catch the shavings. Any helicoil repair I've done involved first drilling the hole to a certain size, then tap that hole to form the new threads. The helicoil is then inserted with either the special tool or it can be inserted with something like needle-nosed pliers.
 
  #8  
Old 06-06-05, 03:13 PM
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Originally Posted by maiden442
So the only way to put in a helicoil is to remove the head? right? I have seen a double tap at the parts store(Auto zone) that starts with the 14mm tap and then follows with a larger tap to put in an insert which comes with it. You then put rtv high temp around the insert and turn it in. Is this the same or different then a helicoil?
A heli-coil is a brand name. It is a stainless steel insert that looks like a spring. The hard part is getting it drilled straight. If they have a stepped tap that starts 14 mm that would be great to get started straight. My only concern is if what little threads you have are strong enough to get the larger tap started. But you have nothing to lose. I would try it. You can get some aluminum thread cutting fluid to make it tap easier and put some grease in the flutes as was said. DO NOT use regular thread cutting fluid on aluminum!!!

Make sure you get some anti sieze on the other plugs and do not over tighten to reduce the risk of this happening again.
 
  #9  
Old 06-06-05, 05:11 PM
maiden442
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Thanks a lot for the info. I will try the step tap with the cutting fluid and the grease and will see where I get.
 
  #10  
Old 06-07-05, 11:51 AM
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Question for Carnut - Why should you not use standard thread cutting oil on aluminum? That is the first time that I have heard this advise.
 
  #11  
Old 06-07-05, 02:44 PM
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regular tapping oil will cake and jam if cutting aluminum threads, use WD-40, yes WD-40 , it will work as good or better than any tapping oil made for alum.
 
  #12  
Old 06-07-05, 06:44 PM
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Originally Posted by thiggy
Question for Carnut - Why should you not use standard thread cutting oil on aluminum? That is the first time that I have heard this advise.
My mistake I said thread cutting fluid. I meant to say tapping fluid, there is a difference. Tapping fluid works the best and is the only type of fluid I know of made for aluminum. I have used wd-40 etc. They are just ok at best in my opinion but aluminum tapping fluid like Winbro alumtap works much better, requires less effort to tap, produces better threads and is less likely to break a tap.

Winbro also makes tapfree for all metals except aluminum.

I have seen tapping fluid for steel actually smoke when applied to aluminum and the tap does not cut well at all. It actually will get stuck and sieze to the aluminum.
 
  #13  
Old 06-08-05, 05:24 AM
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Thanks, Carnut. I'm always learning new (worthwhile) information from the folks on this site.
 
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