I recently performed some maintenance on my bike, and due to some negligence, I screwed one of the spark plugs onto the thread. I have been told that the correct way to solve this problem is to remove the head and run the tap through the hole, or I can use Helicoil. One sounds expensive, the other sounds painful. Is there a cheaper, simpler, and more suitable DIY solution? Can I use some tools at home without removing the head to solve this problem, or am I completely messed up?

Ah, what a nightmare. Cross-threading spark plugs has always been one of my top three bike maintenance nightmares, where I dropped my bike from an elevator and had to do any kind of work on the first-generation Gold Wing. Who told you that the best and correct way to repair a cross-threaded spark plug hole is to remove the head and run the tap or thread chaser through it. People who think Helicoils are a kind of pain are also right. However, there is a cheaper and easier alternative to pulling the head. It is called the back tap, and it works wonders.

Look, I recently screwed a spark plug on my CB450K4-this is the first ride and tightening in 20 years. I am ashamed and heartbroken. Shame, because I fucking know better, heartbroken, because I have invested a lot of time in the old Honda, and it runs like a champion, so the thought of having to pull the engine (you need to do this to get out of trouble) is just Makes me sick. So, after sitting on a stool and staring at the bicycle for a while, I went online to see if there was a way to solve this problem in less than ten hours. The internet coughed up.

The rear faucet is a hollow steel through which a rod passes. One end is threaded and can be expanded by a retractable/retractable plunger. There is a knurled adjustment knob on the other end. As the young man said, the back faucet comes from many different companies (I bought the 14mm Powerbuilt version on Amazon for about $40), whether online or IRL.

To use it, you just need to push the plunger out so that the threaded end is as small as possible and very lubricated, and then insert the threaded end into the hole (after ensuring that the piston is at the bottom of the stroke, course). Then, you turn the knob to retract the plunger that unfolds the threaded end. Retract the plunger until the tap just fits and is inserted into the thread correctly. Then use a wrench or ratchet to slowly and carefully remove the faucet from the hole. Once it comes out, you can clean the faucet nicely, relubricate it, and repeat the process with the plunger retracted a bit further. Do this until the plunger is fully retracted into the tool and the threads are at maximum distribution. If you are careful and lucky, your threads will be repaired and cleaned immediately.

Compared with the traditional thread chaser, the biggest advantage of post tapping is that when you take it out of the hole, all these tiny metal blocks will be dragged out with the grease. This is definitely better than piercing the rattrapante into the hole and praying that the shavings stick to the tool instead of falling into the cylinder. I did it six times with my rear faucet until the whole was cleaned up, and I could manually insert a new spark plug. Not too shabby.

Now, I do have some warnings. Most of my threads are intact, and the damage only extends to about one-third of the threads. If your faucet is badly chewed, completely peeled off, or otherwise badly damaged, the rear faucet may not be the right way to solve your problem. In this case, you may need to pull your head and let a professional tap the hole. In addition, if you don't know what you are doing, you may further damage your threads through back tapping. If you are confident in your painful skills, grasp it and master it. If you are not that confident, please find a mechanically inclined friend or hire a professional to do this for you.