74-Roadster

I overtorqued a intake bolt and ruined the hole. What type of bit do I drill the hole out with? And then I need to tap new threads for the helicoil and insert the coil?

Is that it in a nutshell?

Is ther any reason why I can't just tap new threads and put in a bigger bolt, say 7/16"?

Larry B.

Heli-coils use a different drill size than regular taps. The kit gives you the drill, a special heli-coil tap and most importantly an installation tool. Without the heli-coil tap and tool you cannot install them. You can tap to a bigger size but a good heli-coil repair is better.

Chuck Gongloff

You'll need to buy a Helicoil Kit, which contains a special tap, and the helicoils themselves. The package will tell you which size bit to use. Would not drill out the hole and go bigger. Helicoils require special taps, which have the same threads/inch on the outside as on the inside. You cannot use a standard tap. Buy the whole kit. Chuck

74-Roadster

Well, I had my engine running again for the second time and no leaks . . . A friend said if the bolt is getting some torque, leave it alone and see if everything is okay. So far so good. :D

ddecart

IMHO it's best to do it the right way. Pick up a helicoil kit from the local parts store. Stop in at the hardware store for the right size drill bit. Drill, tap, insert and be done with it for good. It's so simple and relatively inexpensive there's really no reason to Bubba it.

74-Roadster

I've heard completely the opposite. Friends have told me that I will need to pull the head to do it right and then I should probably take the head to a machine shop. My understanding is that drilling into a head in place and keeping the hole plumb is not very simple. :confused:

Also, it's the far corner bolt and the threads are certainly yielding but have not failed. Since no additional force is being applied, only the thermal cycle could add additional loading to cause more strain and failure. So, if it doesn't leak. . . leave it alone. This engine will only serve as a sunny day driver for another 15,000 - 20,000 miles and then I'm putting a new engine in her. :D :D :D

71roadster

I recently did three helicoils in my passenger head. It was a pain but not impossible and after the first one I knew what to expect so the others were easy (about three hous total - header off to header on). Two tricks are, I had to break about 1.5 to 2 inches off the drill bit and resharpen it in order to get the right angle with the drill AND get a variable speed angle drill (cheap rental). You want to drill slow and steady and it will still catch a lot. I don't think getting a PERFECTLY straight hole is absolutley necessary and it is easy to estimate 'close enough'.

also, once one hole goes...others will eventually follow. But unless you get persistent exhaust leak, I would leave it until you do. After I was done the threads were ...oh so nice!