Jonny69
13-09-2007, 12:13
Recently I checked the tightness of the head-studs on my engine, something you should do on a freshly built engine because the headgasket compresses a bit and the studs of bolts stretch a little. Unfortunately I managed to shear one off which left a length of the stud stuck in the block. This is possibly the worst thing that can happen when you're working on a car and I was dreading doing this job. I decided because the head is quite thin on my engine I'd give it a go with the head in situ without taking it off. This also meant I would not risk shearing any more of them when I torqued them back up. I was also tempting fate by taking pictures for the internet. Doomed from the start...
This is the offending item:
http://www.dropfiles.net//files/319/stud_removal/IMG_1780.jpg
Closer inspection tells me it's a hand made stud because comparing it with an OEM stud one can clearly see the difference in the threads. On the OEM machine made item the thread has a rounded profile where it is rolled out and on this broken one the hand cut thread is very sharp. This leaves a nasty concentrated fracture point so this stud is inherently weaker than the OEM one.
These are what I'm going to be using to get the end out the block with. Easy out stud and bolt extractors:
http://www.dropfiles.net//files/319/stud_removal/IMG_1781.jpg
It's a bit like a thread tap except the thread is left handed and tapered. The theory is you drill a hole down the middle of the sheared bolt or stud and wind one of these in until the thread binds then you can undo the stuck end. That's the theory anyway. In practice they have a habit of snapping in the end of the stuck thread leaving you with a drilled out stud with half an easy out stuck in it which is then too hard to drill out. I weighed up the risk/grief ratio and decided if it snaps I'm no worse off than when I started as I would have to take the head off and do the welding method anyway.
So there are a few things that you can do to help things along. First is make sure you drill right down the middle of the stud. I jumped on the lathe and turned up a simple bush to drop down the hole in the head to use as a drilling guide:
http://www.dropfiles.net//files/319/stud_removal/IMG_1784.jpg
You could make it by hand from a short length of bar if you were careful but I had kind access to lathe. The bush drops down this hole:
http://www.dropfiles.net//files/319/stud_removal/IMG_1785.jpg
As you can see it's conveniently chosen to break the stud with the least access. This is a common thing to happen, you'll find you never break anything that has clear access to work on. To make life easier I made an extension bar for the drill, just a length of bar drilled down the middle that I could tack weld the drill bit into so that the drill itself is up away from the bulkhead and the wires:
http://www.dropfiles.net//files/319/stud_removal/IMG_1786.jpg
Another handy hint from someone who knows is to put a punch on the stuck part and tap away at it. Now I know my hammer is mighty and large but actually I'm just tapping it and you want to tappity tap tap away at it for about 5 to 10 minutes. The aim is not to lamb it down the hole but to just lightly deform the threads on the stud so that it will be a bit easier to wind out. Here's me in action. Go me:
http://www.dropfiles.net//files/319/stud_removal/IMG_1787.jpg
Welder up on blow holes in stuff setting and a quick stitch to hold it in the extension and I drilled down through the stud until I broke through. It's worth noting this is a top quality drill because I didn't want it blunting or breaking up in the hardened steel used for the stud. It went through it like butter despite using only my trusty 9V Bosch battery drill:
http://www.dropfiles.net//files/319/stud_removal/IMG_1789.jpg
The easy outs are numbered and for a 3/8" stud you use a no.3 'out'. I loaded it up in a small tap wrench and wound it in. It grabbed the stud and felt like it was unwinding something and came loose and could be turned by hand. I was suspcious that it should be so easy and when it finally came loose and I withdrew it I wasn't surprised to see the end of the easy out had just mashed up and I was clearly just turning it on itself. This was most disappointing so I had a second and third try, this time hammering the easy out into the hole in case I could get a good grip. It was just left looking like this:
http://www.dropfiles.net//files/319/stud_removal/IMG_1793.jpg
I was about to give up but as you do in these situations you say to yourself what have I got to lose... so I got a larger drill out to try the next size up. I had nothing to guide the drill in straight except the existing hole but it went in straight enough and I pulled the swarf out with with a magnetised scredriver. The no.4 out is big enough to use a square brake shoe spanner on which made things easier and as before it grabbed and turned but this time the easy out felt like it had hold of something. I just kept turning and like manna from heaven I was greeted with the end of my broken stud jammed on the end of the easy out:
http://www.dropfiles.net//files/319/stud_removal/IMG_1795.jpg
I can't tell you what the relief felt like, it's an amazing feeling. So after cleaning out the rest of the debris with the magnetised screwdriver I selected a decent stud from the old ones and tightened it in:
http://www.dropfiles.net//files/319/stud_removal/IMG_1798.jpg
This time I took extreme care when cranking up the nut but to be honest the original stud felt a lot more sturdy than my new ones. Celebration was in the form of gnocci topped with leftover bolognese sauce, real parmesan cheese and a bottle of cheap French wine. Do I know how to party or what?
This is the offending item:
http://www.dropfiles.net//files/319/stud_removal/IMG_1780.jpg
Closer inspection tells me it's a hand made stud because comparing it with an OEM stud one can clearly see the difference in the threads. On the OEM machine made item the thread has a rounded profile where it is rolled out and on this broken one the hand cut thread is very sharp. This leaves a nasty concentrated fracture point so this stud is inherently weaker than the OEM one.
These are what I'm going to be using to get the end out the block with. Easy out stud and bolt extractors:
http://www.dropfiles.net//files/319/stud_removal/IMG_1781.jpg
It's a bit like a thread tap except the thread is left handed and tapered. The theory is you drill a hole down the middle of the sheared bolt or stud and wind one of these in until the thread binds then you can undo the stuck end. That's the theory anyway. In practice they have a habit of snapping in the end of the stuck thread leaving you with a drilled out stud with half an easy out stuck in it which is then too hard to drill out. I weighed up the risk/grief ratio and decided if it snaps I'm no worse off than when I started as I would have to take the head off and do the welding method anyway.
So there are a few things that you can do to help things along. First is make sure you drill right down the middle of the stud. I jumped on the lathe and turned up a simple bush to drop down the hole in the head to use as a drilling guide:
http://www.dropfiles.net//files/319/stud_removal/IMG_1784.jpg
You could make it by hand from a short length of bar if you were careful but I had kind access to lathe. The bush drops down this hole:
http://www.dropfiles.net//files/319/stud_removal/IMG_1785.jpg
As you can see it's conveniently chosen to break the stud with the least access. This is a common thing to happen, you'll find you never break anything that has clear access to work on. To make life easier I made an extension bar for the drill, just a length of bar drilled down the middle that I could tack weld the drill bit into so that the drill itself is up away from the bulkhead and the wires:
http://www.dropfiles.net//files/319/stud_removal/IMG_1786.jpg
Another handy hint from someone who knows is to put a punch on the stuck part and tap away at it. Now I know my hammer is mighty and large but actually I'm just tapping it and you want to tappity tap tap away at it for about 5 to 10 minutes. The aim is not to lamb it down the hole but to just lightly deform the threads on the stud so that it will be a bit easier to wind out. Here's me in action. Go me:
http://www.dropfiles.net//files/319/stud_removal/IMG_1787.jpg
Welder up on blow holes in stuff setting and a quick stitch to hold it in the extension and I drilled down through the stud until I broke through. It's worth noting this is a top quality drill because I didn't want it blunting or breaking up in the hardened steel used for the stud. It went through it like butter despite using only my trusty 9V Bosch battery drill:
http://www.dropfiles.net//files/319/stud_removal/IMG_1789.jpg
The easy outs are numbered and for a 3/8" stud you use a no.3 'out'. I loaded it up in a small tap wrench and wound it in. It grabbed the stud and felt like it was unwinding something and came loose and could be turned by hand. I was suspcious that it should be so easy and when it finally came loose and I withdrew it I wasn't surprised to see the end of the easy out had just mashed up and I was clearly just turning it on itself. This was most disappointing so I had a second and third try, this time hammering the easy out into the hole in case I could get a good grip. It was just left looking like this:
http://www.dropfiles.net//files/319/stud_removal/IMG_1793.jpg
I was about to give up but as you do in these situations you say to yourself what have I got to lose... so I got a larger drill out to try the next size up. I had nothing to guide the drill in straight except the existing hole but it went in straight enough and I pulled the swarf out with with a magnetised scredriver. The no.4 out is big enough to use a square brake shoe spanner on which made things easier and as before it grabbed and turned but this time the easy out felt like it had hold of something. I just kept turning and like manna from heaven I was greeted with the end of my broken stud jammed on the end of the easy out:
http://www.dropfiles.net//files/319/stud_removal/IMG_1795.jpg
I can't tell you what the relief felt like, it's an amazing feeling. So after cleaning out the rest of the debris with the magnetised screwdriver I selected a decent stud from the old ones and tightened it in:
http://www.dropfiles.net//files/319/stud_removal/IMG_1798.jpg
This time I took extreme care when cranking up the nut but to be honest the original stud felt a lot more sturdy than my new ones. Celebration was in the form of gnocci topped with leftover bolognese sauce, real parmesan cheese and a bottle of cheap French wine. Do I know how to party or what?