Thought I would ask the experts here. I have a car that got finished for my dad (story to follow), and I ended up taking stewardship of. He worked with the engine builder and all was well upon delivery. That summer, pop decided to fiddle with things, and wound up monkeying with the F/A mixture and checking the plugs. What I see now that I have the car is there are two plugs (no. 2 & 6) which feel cross threaded. I used a borescope to peek in, also was able to use my little finger to remove a s**** of thread 1/4". I found this after pulling the plugs last fall, have not run the car since. Car has about 650 miles on the built engine. I'm now looking to remove the heads, do a thorough inspection and re-install. The heads are aluminum, so the lengthy description is for a simple question: given the situation, would I expect to find any damage to the cylinders? Since its high nickel content cast iron, I'm hoping 'no'. But like I say, thought I'd ask the experts.
They may not be cross-threaded, it may be a case of galling if the plugs were installed dry or without some sort of anti-seize. It's likely that any aluminum bits went out the exhaust...
I doubt that you have done any damage to the cylinders at all. You can inspect if it makes you feel better. I would remove the heads and chase the threads ( they make a tap specifically for that). if you are not happy with the result drill them and throw a heli coil in there.
Go to NAPA and buy a spark plug thread chaser to "clean up" the threads. Don't use a tap. If that doesn't work, remove the heads and install a spark plug helicoil. . It's comes in a kit. Easy to install.
I've done this repair without removing the head when necessary. Call it a Tap or Thread chaser, I use wheel bearing grease and fill the flute's of the Tap. This will gather up any chips or shavings and keep them from dropping into the Cyl. Never had an issue from chips in the hole yet. You MUST use anti seize on all plugs in all Aluminum heads at all times. Any chips made are very tiny and will spit out the exhaust without issues. The Wizzard
I don't know but it seems as though if the plug was cross threaded it would not sit square with the seat. either tapered or gasket. If so I believe you would have a compression leak. If you do Helicoil the plug hole, be careful about getting it square.
I wouldn't remove the heads either. I would do as Pist-n-broke suggest with 2 additons. Before you begin turn the engine so both valves are closed, and after you are done blow out the cylinder with compressed air before reinstalling the spark plug. A short brake line with thread onto your air blower and allow you to put the air right inside the cylinder. Anything inside with blow out the plug hole.
My son-in-law (who has very limited mechanic skills) got a "kit" at O'Reilly Auto Parts for around $35 which was made to repair a stripped spark plug hole in an aluminum head. He successfully repaired it without removing the head. Any thread materials your dad got in the cylinder is very unlikely to be a problem I would say. Maybe a small piece of tubing, duct taped into a vacuum cleaner hose, would allow you to scavenge debris through the plug hole.
I open the exhaust valve while cutting the fresh threads for a helicoil. Then put a shop vac on the tail pipe. Leave the vacuum on the whole time while drilling and tapping, then hit the cylinder with compressed air after, at best it will remove all the metal bits or leave a tiny amount that will work it's way out once the engine is running.
This is good advice, and if I recall, there was a bit of what seemed like oil around the base of the spark plug. I chalked it up to too much anti-seize. The plug hole is pretty narrow and tight for a socket, so I'm guessing the plugs were square on the seat - but that's something I'd like to confirm when I remove the heads. Better safe than sorry, and I'll sleep better knowing things are as they ought to be. Not just hoping. Then again, I'm a bit OCD. For reference, it's in a Pontiac 421, fresh build, with Kauffman D port heads. I'm sure this isn't the first time I'll be asking questions, but hopefully something less stressful next time.
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