didn't see that comming

[G-GAURD]

then the .250 hole is still undersize for the coil?

my main concern is the integrity of the threads. i dont want to put too much torque on the exhaust flange nut and end up pulling the material out of the hole or the thread wall releasing the stud.

well i got the whole bike cheap and knew it neede some attentionthen i will make the attomped

[Snakeoil]

Forget JB weld around an exhaust port. MarineTex might work, but not something I would mess with. Too much heat.

My hole had been tapped 1/4-20, which is .250 major diameter. And there was still enough meat to hold the helicoil.

Before you try anything, see if you cannot put a small slot in the stud with a small chisel and turn it like a screw. Often, the stud is actually loose in the hold and broke due to excess tensile load which went away when it broke. It might take a little patience, buy I've worked them out that way before.

If you have to drill it out....

I would try to put a punch mark in the center of the broken stud and then carefully drill a small hole in the center. There is a trick for doing this to help keep the hole straight. Key to this is getting the punch mark dead center. Then with a 1/16 drill or similar size, start a hole in the stud. What you want is just a short starter hole maybe 1/16 deep or so.

Now, get a piece of steel or aluminum about a 1/2 to 3/4 inch thick with parallel sufaces. Put it in your drill press (hope you have one) and drill a hole the size of the small drill bit you are using. This is your drill guide. Now, while holding your drill guide against the flat surface of the exhaust port. Drill thru the guide hole and into the starter hole in the broken stud. Go slow and clear the chips so you don't bind and break the drill bit. If you are careful you will drill right down the center of the broken stud. Now take your drill guide and drill it out with a 6mm drill in the drill press. Put the guide back in place on the exhause port and drill out the stud with a 6mm drill bit.

You could drill out the stud in stages by starting with a drill bit smaller than 6mm. That's up to you. Each time, open up the hole in the guide block for the drill you are about to use.

When you are done and the stud is out, you can use the block to help you drill the heli-coil hole straight. Then drill out the block to the major diameter of the heli-coil tap and use the block to keep the tap straight when you tap the hold for the heli-coil.

PepBoys has thread repair kits in metric sizes. They are not Heli-coil brand, but identical. A kit usually includes the tap drill, the tap, insert installation tool and about a dozen inserts. I think they are about $15 a kit. I would suggest you get a 6mm kit and an 8mm kit because you will probably need them. Threaded holes for the mirrors and foot peg mount holes are 8mm.

Good luck,
Rob

[Gunner_CAF]

then the .250 hole is still undersize for the coil?

my main concern is the integrity of the threads. i dont want to put too much torque on the exhaust flange nut and end up pulling the material out of the hole or the thread wall releasing the stud.

well i got the whole bike cheap and knew it neede some attentionthen i will make the attomped

I read someplace the Heli-Coil was first made for aircraft engines. The threads in the aluminum blocks would strip out so they used these to strengthen the treads. You will end up with strong thread after you insert the coil. A few Heli-Coil (or similar brand) kits is something your going to need when working on these motors.

Gunner

[Dana01]

I'm a fan of Timesert inserts. I installed them in the heads of my racer in the plug holes, as well as a few other vulnerable Aluminum locales.

But then again, the owner is a friend, I got the factory grand tour, and 1-on-1 instruction in the proper installation. He then sponsored my racing effort with a full Metric thread replacement kit ... so I'm pretty biased ;)

Anyone in the Reno area is welcome to stop by, take a tour and say hi to John.

[davomoto]

Dana, the timesert kits are on a whole different level then the heli-coils! I have one I purchased used on ebay, for 10mm spark plug holes. They use an entire collar, rather than just a wire insert. The potential downside is the hole has to be enlarged a lot more that with a heli-coil, and they are not cheap!

Davo

[Snakeoil]

We use Heli-coils on our turbines for most of the key threaded holes, including couplings. I remember back in the 80's a company called Keensert came to our offices and did a pitch on why their insert was superior to a Heli-coil. It might be in some applications. But it really just appeared to be a different design to get around Heli-coil's patents and lock on the market at the time. We still use Heli-coils, by the way.

What I like most about the Heli-coil design is it is self-locking. The more you try to unscrew it, the tighter it gets. That spells success to me.

regards,
Rob

[Dana01]

I love this topic. Probably every type of restoration board on the planet eventually gets into the pros and cons of Heli-Coil vs Time Sert.

One advantage of TS is that yes, it uses an entire insert instead of a thread filler strip, but IMHO this provides a HUGE biting surface over the HC thread. Unlike HC, The insert can't come back out because it's "swaged" in place, and they are very difficult to strip. You actually create the last few threads during the install procedure. A further plus is that that insert is now steel compared to the original Aluminum base material.

Yes you need a bigger hole, but you don't need to drill and tap. The insert comes with a hand drill/tap tool set which works nicely on the soft Al. In the case of header studs, there's plenty of meat to accommodate an insert.

Downsides ... yep .. they are pricey, and yes they aren't as available in stores like HC's.

Open invite: If anyone in Norcal ever needs a stripped thread fixed and can get the part to me, I'll happily do the repair in my shop. I have a nice supply of metric inserts.

Have fun :)