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Damaged Spark Plug Threads in Aluminum Head
I stupidly damaged the first couple of threads in one of the spark plug holes. I ran a thread chaser through, and that appears to have fixed it. The plug goes in ok, but seems not to snug quite as tight as normal. This may be just my timidity, not wanting to completely strip the threads in the head. Assuming the current fix proves unsat, does anyone have suggestions for a better solution?
Many thanks, Jerry |
Weld and redrill & tap, or Heli-Coil. What make is the head?
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Helicoil...
Bring the piston in that cylinder up to top dead center and tap/install helicoil. Tape a piece if 7/16" fuel hose up in your wet/dry vacuum cleaner's hose to make it "air tight", duct tap works fine for the seal and suck out the chips inside the combustion chamber. There's always an element of risk in a chip getting wedged between the piston edge and the cylinder, though minimal at worst. The only other way is pulling the head. BTW... Helicoil makes inserts specifically intended for spark plug hole repair.. Dave |
Heli-Coil is the best way to setup an aluminum head.
Make sure you loc-tite the coil(s) in place after you do the fix. Undy's info is pretty much the way I do it. After the coil(s) are set, make sure to use Cop-seal or some other anti-seeze paste so they can be removed. Hope this helps. |
grease
if you go the heli-coil route and don't want to take the head off...
The groves in the drill bit and tap are designed to allow waste material to escape. By filling those grooves with grease, both the drill bit and the tap will collect most of the chips - downside, the greasy chips that escape can be harder to capture, upside of the downside is that they don't travel - sorta hit and stick. smith |
If it makes you feel any better...
Ford had (has) problems with the 4.6 and 5.4 engines spitting out the plugs, along with the threads, particularly on the lightning engines. They sell a threaded insert (helicoil, pretty much) kit that you install in-place without removing the head. Either that same kit, or something like it, could certainly be made to work.
However, if there's enough thread there to avoid having to do this...I'd antisieze the plug, screw it in, snug it up, and run it. If it can't hold, you'll know in short order. If this is a street engine that can go a long time between plug changes, I'd consider putting platinum plugs in it and changing the service interval to something a lot less frequent to avoid disturbing that plug. I've seen 70,000+mi old platinum plugs that showed near zero wear. The thinking here is partially lazyness; but also practicality. In 70K miles, chances are better that the head is coming off for some other reason and you can fix it the more durable way at that time. Why do it twice if it'll hold til then. Byron |
Great advice! Thanks everyone. Quickjack, it's an AFR 205 head.
Jerry |
Jerry;
I just finished installing inserts in just about every orifice in my 205's (not by choice) and I can offer two bits of advice beyond what everyone else had to say. First, use Heli-coil brand inserts. The ones you buy at the local auto parts convenience stores are cheap and don't install well. The Heli-coil's are more expensive but worth the money. Second, when drilling out the old threads don't start with the drill bit in the kit. Get out your bit register and start with a smaller size, then work up to the right size. When using a hand-held drill it's more than easy to drill the hole at the wrong angle, especially on small holes. Take your time and have fun! Bill Stradtner |
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