Stripped header bolt hole. Can I repair w/o taking out the engine?

Question

So I installed new headers onto my 95 mustang GT with a friend who "knew what he was doing" until he stripped one of my manifold bolt holes. I know I can either insert new threads or tap and dye it, but I want to know if I need to pull the engine to get to it. Any advice is much appreciated!!!

Answer 1

Yes, you can do it, if you have sufficient access to the hole. A tap with handle is going to be around 2"-4" long. Do you have enough clearance to get it in place, perpendicular to the surface of the head? If not, will lifting the engine slightly - remove engine mount nuts, lift engine with your floor jack - give you enough room?

Another question: How many bolts hold the manifold to the head? You might be fine just leaving that one out. (Not what I would do, but it might work.)

Regarding tap & "dye": You don't need a die. That's for the completely opposite problem.

This is what a competent machine shop would do, rather than replacing the head.

There are a number of YouTube videos online about how to use a tap, but the idea is:

• Clean the hole as best as possible.
• With the tap installed in the tap handle - I would NOT use a drill for this application - turn the tap into the hole until it starts to really resist. Taps are easy to break - you don't want to have to drill out a broken tap and start over. (I have a broken tap embedded in one of my engines. It adds weight and makes the car slower.)
• Unscrew the tap from the hole, blow off any chips (aka, metal debris) that you see.
• Screw it back in.
• Repeat until you've reached a sufficient depth.

Note that you might have to use a larger tap than the stock hole, depending on how trashed the threads are.

There is another option called a "helicoil" which should let you put threads back in the same size hole. That would require cleaning out the existing threads, but it'd let you keep the current bolt size. (... which is really only an issue if the holes in your manifold are tight and you don't want to drill them out to the next size up.)

If you haven't done this before: call a local machine shop and ask them what they'd charge, and make sure they're willing to do it with the engine in the car. This is one of those things that's very easy to mess up. If you're not comfortable with the process, it's probably better to get an expert involved. $100-$200 to repair a hole is a lot cheaper than a new engine.