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How do I remove broken off head bolts?


OlderThanMe

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I have three head bolts that are broken off right above the block's deck surface. I have an easy-out but it is a little small for a big bolt like the head bolt. What methods are there for removing broken head bolts?

Even I have to take the block to a machine shop I want to know how they will remove them and how much they should charge. I have heard of upto $10 per head bolt removed...

I thought about using a vice-grip on the bolts but I don't want to scratch the deck surface.

 

I am going to replace the bolts with studs once I can get these old bolts out.

Thanks guys.

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Well, If I were you I'd drill the bolt on center after getting a good center punch hole to start with. Then I'd smack it a couple of good raps with a 3lb sledge. Then I'd heat it with a propane torch and melt some wax into the threads. Should screw out relatively easily. If not well, at least you tried.

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I just did this on a block. I used a MIG welder to weld a 3/8 bolt to the head bolt. I first ground the tip of the 3/8 bolt into a cone, to maximize surface area for the weld. Then I welded the 3/8 bolt to the busted head bold, using as much weld as I could to make it strong. I let it all cool for 15 minutes or so, then heated the block around the broken bolt with a MAP torch. I put a pipe wrench on the 3/8 bolt, and the whole thing came right out.

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I was increadibly lucky when I had a head bolt break off on me... it looked very similar to the picture you have and I was going to take the whole thing to a machine shop but I decided since I had a pair of vice grips handy I would give them a try before pulling the engine and the bolt came right out. If you don't get as lucky as me I can say that melting wax as described by Doc is one of the best ways out there to get a stuck bolt out, I have used that trick many times over the years and it has always worked.

 

Dragonfly

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You could also drill it in it's center, heat it red hot then pour a bit of water in the hole, since you drilled, the metal around the hole will have more room to contract.

Since metal allways contract more than it expanded, it should come loose by itself.

What really helps in z-ya's technique is the heat from the weld itself.

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I have found that often bolts break off and you can just turn them out with a pair of vise grips pretty easy. No heat but lube usually helps. You might find that the bolt is not even "stuck" and will just turn out.

 

I only have problems when I trying to take a rusty bolt out of a rusty hole. Then you get bolts that break off and the threaded part gets stuck/seized, this usually when it gets to be a PITA!

 

 

Guy

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Many of these suggestions should work for you. The problem is if any one of them fails you're usually hosed to try anything else. Here's how I typically deal with a broken bolt when material is still exposed above the surface. I take a piece of round stock (1" long is good) and drill a partial hole to just fit over the remaining stud. I then drill a smaller pilot hole all the way through the round stock. That hole is often the same diameter as the bolt at the valley of the threads. The idea is to make a guide which allows you to accurately drill all of the material out except the threaded portion. Once done, a tap is used to clean the hole up. I keep the guides for future use. A machinist could make up several of these with some standard partial holes (8mm, 10mm, 12mm, 1/4", 3/8", etc.)rather quickly with 1/8" and 1/4" pilot holes. Once the pilot hole is drilled in the broken stud you can progressively step up the drill size to remove material until the threads are just reached.

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