Broken bolt

[erikgreen]

I was cleaning up my Chevy 350 block getting ready to put it back together with Marine gaskets and bolt-ons, when I discovered that one of the head bolts was broken off.

Apparently it was broken off by the previous owner and left in... the engine ran without the bolt in.

Being the anal type I am, I decided I wanted to get the bolt end out and put a new bolt in its place. So I went and bought a titanium nitride drill, and a bolt puller sized for 1/4" drill bits.

I drilled the center of the bolt out, then following the directions on the puller I tapped it into place, hitting it lightly 3 times. The third tap the bolt puller snapped off!

After expressing my disappointment at this development with a few choice words, I tried drilling out alongside the bolt to either side... I figured I'd damage the hole a bit, but I could weld it or even JB weld to fix it, and at least I'd have the bolt out.

No luck. So now I have a block with one bolt I can't use, and I can't see a way to get the broken bits (which includes part of a super-hard bolt puller) out.

Do I need to get a new block? I just sold my extra 350 block Any chance I could run for a season without using that bolt hole? Like I said, the block ran before.

Suggestions deeply appreciated. Here are a couple pics of the problem.

Erik

 

[Limited-Time]

Re: Broken bolt

You do have some options here. But I would not try running the engine sans one head bolt. The seized stud (including broken bit) can be removed using a Dremal (sp) tool and correctly sized grinding bits. Care must be taken when using the method. If you can grind out the hardened bit you broke off in the stud it may be possible to remove the remaining part of the bolt using a LEFT handed drill bit. You need to be careful and stay as close to the center of the bolt as possable. Also use the largest left handed drill bit you can without cutting into the threaded area. Good Luck!!

 

[95yj]

Re: Broken bolt

Ouch. That's the one thing that sucks with easyouts. If you break it off, you're finished because it's pretty tough to drill through hardened steel.

For future reference, when trying to remove a stuck bolt with an easyout you want to drill it out with the largest possible drill bit you can use without getting into the threads of the bolt hole. I may not be seeing the picture correctly, but it looks like there is still quite a width of the original bolt in there. The more bolt you remove, the less tension there is holding it in and therefore the less chance of breaking off the easyout. I've had bolts that wouldn't budge and after drilling with 1/16 larger bit, they just threaded right out.

With no other options, I would take it to a machine shop and have them drill the entire bolt out with a drill press. Then tap new threads or try helicoils or both to be able to secure another bolt. Running with a head bolt missing is gonna cause problems sooner than later.

 

[erikgreen]

Re: Broken bolt

I've been trying to mig weld a nut on the top of the stud like it says here:

http://www.thebugshop.org/bsfqtool.htm

Not much luck so far, probably because my mig welder isn't the best, but the idea seems sound.

Paying a machine shop to drill it out really isn't an option, I'm out of money at this point. If I can't get it out myself, I'm stuck. I might see if I can trade my ford 302 motor for a chevy block somehow.

The stupid thing is, I just sold my "other" chevy 350 block that I got free, because this one was in better shape and I needed the money more than the block. :\

 

[wire2]

Re: Broken bolt

A machine shop/drill press means pulling the outdrive and the engine.
It can be done in place with a rented magnetic base drill and a carbide tipped bit. Get a tin of drilling/tapping fluid to keep it cool.
If you know a local toolmaker, enlist his help.
If you happen to damage the existing thread, as mentioned, a Heli-coil will fix it.
I prefer Time-serts myself. They're a 1 piece bushing style that fits in a recessed shoulder and swages into place with an install tool. Very permanent.

 

[erikgreen]

Re: Broken bolt

Well, the engine isn't in the boat yet... I wish it was almost.

I do have a drill press of my own. Tomorrow I'll try drilling out the whole thing, including the bolt part and the easy-out.

Does anyone know the relative hardness of an easy-out vs. a cobalt alloy drill bit? If the cobalt is lots harder it may work. I'll use lots of cutting oil to help.

If that doesn't work, I will have to try to find a 350 block somewhere. If anyone knows of a place to get one in the Twin Cities, MN area, please let me know. I am looking to pay $200 at most, which is gonna make it hard to find something (not to mention hard to eat for a week... but damn I want this boat in the water!)

Erik

 

[wire2]

Re: Broken bolt

The mig welded nut is a very effective solution, I've used it several times. One of the reasons it works well is that the stud is super heated by the arc and tries to expand, but is contained by the threaded bore. Then it cools and shrinks. The expand/shrink will usually release rusted threads.
When a mig is not available I've also used a simple stick machine with a 3/32" stainless rod at 90 amps.

 

[erikgreen]

Re: Broken bolt

The problem I have with it is that the bolt is broken off about 1/8 inch below the surface.. plus my previous attempts have left two "ears" at the sides of the bolt that I have to fill with silicone so the mig doesn't flow metal in there and lock the bolt in place.

So I fill them with silicone, clean the top of the bolt shiny as I can, then mig weld a nut on. Usually it adheres partly, then breaks off when I gently try to turn it. I'm going to buy 20 or so steel (ungalvanized) nuts tomorrow and keep trying.

The other thing that was recommended to me was using a solid carbide drill bit in a drill press to clean out the hole completely. But solid carbide drill bits are hard to find, I'd probably have to order one online.

Any idea if repeated heating via MIG will hurt the engine block?

Erik

 

[WaterWitch2]

Re: Broken bolt

The mig welded nut is a very effective solution, I've used it several times. One of the reasons it works well is that the stud is super heated by the arc and tries to expand, but is contained by the threaded bore. Then it cools and shrinks. The expand/shrink will usually release rusted threads.
When a mig is not available I've also used a simple stick machine with a 3/32" stainless rod at 90 amps.

I've sucessfully used the MIG trick too a few times on broken bolts. It also works well when you lose the key for locking lug nuts.

 

[wire2]

Re: Broken bolt

Waterwitch, that happened to me earlier this year, the McGard key broke while taking 1 off, had to weld a 3/4" half size nut on the other 3.

Erik, there's very little heat going in to the block from this operation so no prob. Plus it's made of cast iron, a mig weld will not stick very well anyway. If you forget the silicone, a tiny bit of block material may pull away, not an issue.
Countersink the upper side of the nuts in a drill press to give you a bit more room to start a weld. Or use a 9/16" nut on the 1/2" stud.
As the article says, turn the heat up for more penetration. (not wire speed). Then let it cool on its own for max shrinkage.
Solid wire/gas works the best, flux core has a hard time floating all the flux up in a plug weld.

 

[erikgreen]

Re: Broken bolt

Well, I managed to find a solution.

The mig welding didn't work after four tries, possibly because the remaining bolt was too countersunk into the hole.

I went and bought a solid carbide drill bit from the local used machine tool dealer, and using that with a lot of dark cutting oil drilled out the remaining part of the easy-out and the bolt. The solid carbide bit went through the hard easy-out fragment like a knife through butter. Very handy.

Then I re-drilled with a 3/8 cobalt bit to size, and re-tapped with the appropriate size tap.

The hole is now slightly off center of where it was, but it does have threads and with a bit of resistance a bolt will go through the original head hole and seat in the new hole.. I think the difference in placement of the hole is probably a few thousandths.

In the future, I'll just try the MIG trick first, especially if there's enough bolt left to do so.

If not, I'll skip the easy-out entirely (heard too many bad things about 'em) and drill out the bolt part with cutting oil.

So, I'm going back to assembling my block. Wish me luck until I find my next problem.

Erik

 

[mudweiser]

Re: Broken bolt

Something that might be worth looking into is a process called time-sert. It's common to have this done on Cadillac Northstar aluminum block engines when the treads on the block pull out. The kit far exceeds a heli-coil and is the only OEM approved kit for Cadillac. The kit includes and plate that is bolted in place from your existing bolt holes, bushing, drill bit, insert and tap. You can't drill sideways or off center due to the bushing and plate. You can drill the hole oversized and tread the insert in back to OEM size. Many kit's are available. Might be worth a few minutes of research: http://www.timesert.com/