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- 3 May 2004
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- Kapitalist Republik of Surrey
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:
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:
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:
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:
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:
This is the offending item:
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:
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:
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:
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:
.
