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Car Forum / Honda Cars / June 2006Cross threaded Spark plug threads
I was replacing the spark plugs in a 1989 accord, something I've done many times on many different vehicles. It's never been a problem until this instance. When I used the socket to loosen Plug #1, it eventually loosened but didnt screw out with ease. The other plugs 2-4 came out with ease and I installed new plugs in them, however everytime I attempted to install the new plug in the first plug hole I couldnt get it to screw in. It just wouldnt catch. I then used a light and have determined that the threads on this first spark plug hole were cross threaded last time the plugs were changed (by a mechanic) I also noticed on the block around this spark plug hole its kinda black and the other 3 spark holes arent black on the metal outside their hole. Has anyone ever ran into this situation and if so how did you solve the problem. Someone I work with suggested I get a 14mm thread chaser and I tried that and it wont catch either... cant repair any of the threads if it wont screw in. Any help or comments would be appreciated. >Has anyone ever ran into this situation Yes, several decades ago on an old Ford push rod V8. >and if so how did you solve the >problem. Someone I work with suggested I get a 14mm thread chaser The thread chaser worked great for me. >tried that and it wont catch either... cant repair any of the threads >if it wont screw in. Any help or comments would be appreciated. If you can't make it work, you are probably looking at a new or rebuilt head. I doubt that a Helicoil would work, but even then you are going to have to remove the head. Hope this helps Man that's terrible. That's one reason I always change my own plugs out and everytime I get a new used car have that fear of the first time I pull them out and check them. Keep us informed on how you fixed it. >>Has anyone ever ran into this situation > [quoted text clipped - 13 lines] > > Hope this helps >>Has anyone ever ran into this situation > [quoted text clipped - 13 lines] > > Hope this helps A thread chaser is not likely to be useful on the aluminum head; the remaining metal won't support the spark plug well enough. Got the tee shirt on that, just with worn threads! Helicoils work superbly in aluminum heads, and the head doesn't have to come off. Some people (including the pros where I used to take my cylinder heads in Phoenix) advocate not worrying about the aluminum shavings; they blow out when the engine is started. More commonly, people put the engine on the beginning of the compression stroke for that cylinder and squirt a bunch of shaving cream into the cylinder. They do the tap and helicoil thing and then turn the crank until the shaving cream, with the shavings, is expelled through the spark plug hole. I suppose they change the oil soon afterward <8^P All in all, you may want to have a cylinder head shop do the work. Fewer unknowns that way. Mike >>>Has anyone ever ran into this situation >> [quoted text clipped - 17 lines] > remaining metal won't support the spark plug well enough. Got the tee shirt > on that, just with worn threads! you got unlucky. if done right, the chaser works perfectly - it depends on whether it was started where the original threads started or whether it cuts a whole new thread - /then/ you don't have much supporting metal and the helicoil is essential. if the head's already off, you can chase from the piston side as the crossing hardly ever gets all the way to the bottom of the hole. use a plug from the piston side first too to force as much of the old thread back into shape as well. > Helicoils work superbly in aluminum heads, and the head doesn't have to come > off. Some people (including the pros where I used to take my cylinder heads [quoted text clipped - 10 lines] > > Mike >> A thread chaser is not likely to be useful on the aluminum head; the >> remaining metal won't support the spark plug well enough. Got the tee [quoted text clipped - 7 lines] > of the hole. use a plug from the piston side first too to force as much > of the old thread back into shape as well. Not so much unlucky as I made a poor choice - it was in a Lotus with a Renault engine, and the threads were not even crossthreaded, just worn out. I wasn't even accelerating hard when I heard a POP and a sound like a lawnmower... the plug had probably been in for months at that point. Maybe a Honda head is more robust and not as sloppy. Mike >>>A thread chaser is not likely to be useful on the aluminum head; the >>>remaining metal won't support the spark plug well enough. Got the tee [quoted text clipped - 10 lines] > Not so much unlucky as I made a poor choice - it was in a Lotus with a > Renault engine, those are quite a good little engine! > and the threads were not even crossthreaded, just worn out. > I wasn't even accelerating hard when I heard a POP and a sound like a [quoted text clipped - 3 lines] > > Mike i've seen this on a honda head - plug had apparently been loose forever. eventually the plug just pulled/wore out the last few threads, and then, as you say, loud chugging noises. as long as there's enough thread to hold the plug, it should be ok. the seal comes from the gasket/washer on the plug and bolts only need 3 threads to hold under most circumstances. >>Has anyone ever ran into this situation > [quoted text clipped - 10 lines] > If you can't make it work, you are probably looking at a new or > rebuilt head. I doubt that a Helicoil would work, helicoils work just fine. > but even then you > are going to have to remove the head. no, it's done in situ. > Hope this helps > Someone I work with suggested I get a 14mm thread chaser and I > tried that and it wont catch either How do you mean "won't catch"? You can't get the chaser to bite into the metal and it keeps spinning in place?  SignatureTeGGeR® The Unofficial Honda/Acura FAQ www.tegger.com/hondafaq/ > I was replacing the spark plugs in a 1989 accord, something I've done > many times on many different vehicles. It's never been a problem until [quoted text clipped - 11 lines] > tried that and it wont catch either... cant repair any of the threads > if it wont screw in. Any help or comments would be appreciated. Hi, There are specialty tools that would make your job a lot easier. I work at a small engine shop and we regularly face this problem. I bought a nifty thread chaser from Lawson Products that is adjustable for hole size, you can collapse it to fit into the hole, insert five threads or so deep, expand to cut and it cleans the threads on the way out. Works very well. By starting in the good threads it works a lot better than starting on the damaged threads. When you use this tool on an assembled engine, hook up a shop vac or vacuum cleaner on the blower side and pressurize the exhaust, turn the engine slowly until air blows out the plug hole and chips won't go into the cylinder. The only drawback I can see is it may be necessary to remove the valve cover to get it into the plug hole and see what you are doing. I also suggest that you try it out first on a nut near the same size to familiarise yourself with the way it works and to develop a good "feel" for how it works. Good luck Scott > > I was replacing the spark plugs in a 1989 accord, something I've done > > many times on many different vehicles. It's never been a problem until [quoted text clipped - 29 lines] > Good luck > Scott This used to be a common malady with VW beetles. Often, the cure was reaming and tapping the hole to an oversize to accommodate a helicoil. That would be the option if the threads cannot be cleaned up. JT |
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