I know i did a bad thing. I tried to put the damper on with the damper bolt. I got the damper on but when i tried to get the bolt out it snaped off in the end of the cranck. I need help now. Can I drill it out and tap it, and what size drill and tap do i need to use. It is a small block chevy 400.

Thanks,
Terry

You could try using an EZ Out first. If you are sucessful then no taping will be required.

If the threads are fairlly damaged from installing your dampner with them, the bolt will be seized to the crank. You can try an ez out first but be very carefull how much force you use to back out the bolt. If you snap the ez out off you will be in a lot worse shape than you were before. The most important thing here is that you drill the hole as close to center as you possibly can. use a cobalt drill. you can use a W(.386) size drill to drill out the bolt and retap it to 7/16-20 but you again run the risk of breaking the tap as it gets jammed up trying to clean out the remains of the bolt threads, then you are in worse shape than you were again. If it were me, I would drill out the entire bolt with a 29/64(.453) drill then tap it using a 1/2-20 tap.

good luck, Rob

Thanks for the help guys, I will never do that again, I hope. I will let you know how it goes.

Thanks,
Terry.

I hope you are good with a hand drill, otherwise the chances of hand drilling a bolt out of the end of a crank without drilling into the crank are slim. Better get a second set of eyes to help line things up. You'll have the best luck with a long smaller diameter drill, say quarter inch, to start with and then step the size up from there. Use cutting oil and clear the threads often. Do not try to drill it all at once because the drill will be harder to control. You will likely need to drill it all the way out and re-tap because if the bolt snapped on the way out, it's pretty likely that the threads are screwed up. You may have no choice but to open it up to a 1/2-20NF thread but only do that as a last resort. I'm a machinist and have drilled out many broken off bolts, but doing it by hand is a challenge.

Tom

Follow figbashs plan. If you can find one try using a 3/8" left hand bit as the final drill. Don't even consider using an EZ-out. If that bolt is siezed to the point that you twisted the head of it off there is NO chance an EZ-out will help. IMHO every EZ-out on the planet should be collected and melted down into something useful..like a doorstop.

agreed, easy outs very seldom work. basically they are just for situations where you broke a bolt off NOT due to it being siezed. like if you bumped a bolt and busted it off.
i don't know how much bolt is sticking out, but welding on a nut to it might give you what you need to turn it out. if not, a SB crank new is only a couple hundred bucks.

I've never in my life, had an EZ-out work.

if you can get the damper back off, you should be able to get a Vise Grip on the threads. Grind the threads off two edges so you have a flat surface to grab. otherwise, it'll just continue to round the bolt threads. Get some penetrating oil in the threads.

If that fails, Drill it out and re-tap it using the above instructions.

I'd drill it out with a lot smaller drill than 1/4" to start. I'd start at 1/8". I beleive you have to relieve the pressure you possibly developed in tightening it too much when you broke the bolt off, thus drilling to the base depth of the thread. I wouldn't give up on an easy-out too quickly. I'd at least try it. Tap it in with a hammer slightly to give it 'teeth" in the bolt.
If that doesn't work, I'd go up in drill sizes in very small increments until I got around 5/16". Then I'd use a 3/8-16 LEFT HAND tap. Hopefully, while it's cutting the thread (Counter Clockwise), it will pull out the remaining piece of the bolt.
I've seen it done many times this way successfully in the machine shop I worked for for 22 years.
___________
Dave
TC #4334
Aces #8193

Don't even think about getting it out with an easy out.
I've repaired several cranks where guys have done the same thing. tried to use the crank bolt to draw in the damper. Big no no. As the bolt is tightened, it begins to pull threads. Then when the bolt is backed out, it binds up becasue it is galling the threads in the crank. You'll never save those threads.
Start your drill bits out small. 1/8" is good. The graduate your drill bits up to the size needed for the 1/2-20 tap. I believe that would be 27/64.

This drilling can be done by hand. A good way to make sure you are straight to the snout is to tape two short pieces of wood or metal to the crank snout so that you can keep the drill bit parallel.

Use caution when tapping the hole. You'll want to run the tap in a little at a time and back it out frequently during the tapping procedure. If you feel any binding, back the tap out, clean it and start again. It helps if you use a round wire bottle style brush with some carb cleaner or the like and then blow out the hole with compressed air periodically.
The worst that can happen is for the tap to break off in the hole. Expect tis to take a while to fix.

I was mounting a damper and pulley on a 350 just today and almost drilled and tapped the threads to 7/16-20 because the first part of the threads in the crank was bad. I cheated and drilled off the first 2-3 threads and was able to install the bolt and it held torque.

The threads in the crank snout are very deep. You might possible be able to drill out the damaged threads and use the threads that are in behind that. It would require a longer bolt, but you have to buy a 1/2" bolt anyway.
You might try removing the broken bolt and see how many threads are left inside the crank. Might be enough to cheat. Good luck!

Make a drill bushing to center the drill on the end of the crankshaft. It would fit inside the balancer bore with a drilled hole in the center. Anyone with a lathe could make this for you. Once you have centered hole you can go up in drill sizes to the tap drill size (without the drill bushing). Maybe an ez-out will work once you have drilled through the length of the broken bolt and relieved some stress but I don't think the left handed drills will work until you get close to tap drill sizes.

If you graduate your drill bits from small to the size you need before taping the hole, the hole itself will act as a guide for the final drill.

I've drilled several cank snouts by hand and once you get to the threads and drill out the last little bit of the broken bolt, the drill should follow the existing threads behind the broken bolt. I doubt it went in very far. Crank snout threads are about 1-1/2" deep on a SBC.

Even if you drill a little off, the hole is so long that as you graduate the drills, the hole should straighten up. You can even be a little angled.

You might even see if the drill size for a helicoil is smaller than the drill size for the next thread size. You may be able to helicoil the hole back to the original 7/16X20 thread.

I have done this before. I used an EZ out and it worked just fine. The bolt even had red thread lock on it.

You'll get it. One word. Patience.

You will have to remove the radiator and maybe even the core support. Course, this thread is several days old now so perhaps you probably did that already.

easy outs work just fine if used as intended.don't use the smallest easy out on a large bolt.use the largest possible and some brain power.if your having to use to much force then the easy out will break:clonk:.buy a set that has the matching left hand drill bits included.alot of times the bolt will back out with the bit.good luck
eric:beers: