Cross threaded Spark plug threads

Yes, several decades ago on an old Ford push rod V8.

The thread chaser worked great for me.

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

"Cali89Honda" wrote in news: snipped-for-privacy@f6g2000cwb.googlegroups.com:

How do you mean "won't catch"? You can't get the chaser to bite into the metal and it keeps spinning in place?

"Cali89Honda" wrote in news: snipped-for-privacy@f6g2000cwb.googlegroups.com:

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

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

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

helicoils work just fine.

no, it's done in situ.

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.

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

those are quite a good little engine!

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.