Broken Head Bolts

Hey guys, I have been working on an old Dodge Flathead 6 that I acquired. It has been sitting maybe 20 years. I did the usual things and got it running , but rough,had a stuck exhaust valve on #2. And I do mean stuck !! Tried everything to soak, heat , wiggle , tap, wouldn't budge. I had to pull the head, even then it was a struggle to get the valve moving freely. Anyway, in spite of all my precautions, I still had 2 head bolts snap off. At first , I thought I was lucky that there was a 1/2 inch of broken bolt above the block surface. I cleaned, heated, soaked, and welded nuts on , but the studs merely snapped off below the welds. I welded on more nuts, same thing. I think the metal is just to degraded to hold. Now I am left to drilling them out. My idea is to buy one of those small drill stands that hold a hand drill and modify it so I can fasten it down to the block deck with bolts and then progressively drill holes in the old studs til I can pick or tap the remains out. They are SO rusted in I don't think any extractor is gonna work. I have never had the weld a nut on trick fail me before. Good plan ? Am I missing something ? Thanks !

What size head bolts? Cast iron block? If so, Drill a pilot hole and blow 'em out with a torch. Tip the block on it's side first.

Hay try this , see if a shop or rental place has a Manibolt Driller, this is a pretty cool tool
Wayne

The bolts are 7/16, turns out they are almost the same as a small block Chevy short head bolts, which I have plenty of, so I can use those as replacements. The block is cast iron. The engine is still in the truck , so no tipping or torch. Some holes are blind and some go into the water jacket. I believe the offending bolts are the ones into the water.

Break out the COLE drill or a magnetic base drill and start as close to center with a small bit increasing slowly until you can see the threads show through and pick them out. If some of the old bolt is sticking up you can some times use a coupling nut and a transfer punch for a true start.
steve

Ooooh, sounds like fun then!! LOL, wait, that's not funny...

try welding a washer to the broken stud then the nut to the washer, you wouldn't believe how much better it works that way.

I would suggest looking into borrowing or renting a magnetic base drill for this. Makes precision work much easier.

When you heat it or weld it, apply candle wax as it cools. Might need it more than once. It"s never failed me. If drilling it out, the mag drill is a good option.

Thats exactly how I do it. drill a small hole use the torch and blow it out, the torch won't cut the rust. then use a tap to clean out the slag.

Try a lefthanded drill bit. I had good luck dilling a small hole then progressivly enlarge until it backs out or stop at threads and cut the remainder with a tap.

I really doubt manibolt makes a template for that old of an engine, they generally cater to motors prone to breaking studs on manifolds and such, head bolts rarely break, especially on a motor of that era

One trick I have used is to make a drill guide block.

If you have access to a Bridgeport mill, or even a good, straight drill press, get a block of steel about 1 1/2" thick, drill a known straight hole through, then drill another hole large enough for an adjoining bolt to go through. Line up the first hole over the broken bolt, bolt it down with the good bolt. This will hold the drill centered and straight over the broken bolt. Once you get a pilot hole drilled, open the drill guide to the size tap drill you need, drill it again.

If you can get to a Bridgeport, you can even use the head as a pattern to know the exact location of the broken bolt. Make a block that will span 3 holes, with the broken bolt in the middle. Use flat head bolts to hold the block down, and the center hole will automatically be centered over the broken bolt.

Yes I have used left handed bits with success before. I only have small sizes however, not big enough for these incredibly stuck ones. Thanks

I hadn't thought of that one, that's a good idea . I may be able to get a better weld on it that way. Although I am thinking the metal of the bolt is so weak it may just snap off more again. But I am gonna try it ! Thanks

I did try candle wax, no luck. I think there is a big glob of rust at the end of the bolt that protrudes into the water jacket making things worse. I don't have access to a Bridgeport or Mag Drill, but could rent . Thanks !

I like the idea of making a drill guide from the bolt pattern on the head. Drill increasingly larger holes until you see the top of the thread poking through on one side. Even with the drill guide you probably won't be lucky enough to drill the hole in exactly the center so the threads will show on one side first. At this point you can often tap the remaining metal with a punch or chisel and it will give a little. On really stubborn ones I have used a jig saw or even a hacksaw blade ground to fit into the hole and sawed through the threads to provide "give" for the rest of the broken part. I know, you say "saw into the threads"? It is only a narrow cut and usually the thread depth will more than make up for any strength you are removing with the saw cut. On a 7/16 screw I would bet you are going to have 3/4" or more thread depth, twice the thickness of a nut. Usually you can carefully tap the hole deeper too by using plug and bottoming taps and get more thread depth if you feel it necessary. This may help anyway if you feel you have damaged the threads in a serious way in removing the broken part even if you don't use my method of sawing into the threads. Then screw a cap screw into the hole until it lightly bottoms, measure how much it is from the block to under the head, compare with the thickness of the head and adjust so you are not bottoming out the cap screw, you will also be adding the thickness of a head gasket. Give it a 1/16 or so to be sure and you now have more thread engagement than before.

(quoted from post at 20:36:13 09/19/16) try welding a washer to the broken stud then the nut to the washer, you wouldn't believe how much better it works that way.

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I like welding a washer on first. Then I normally use a larger nut so that I can get a lot of heat transferred into the broken bolt. They usually come out after they cool down.