Stripped thread in the block - Help!
Discussion
Putting a cylinder head back on (BMW 523i) and didn't even get two of the bolts up to the jointing torque (40Nm) before it became apparent that they werent going in any further. Undoing them; same effect. Managed to remove the bolt and the thread has come with it. Any ideas how this could have happened? And probably more importantly: What the hell do I do now?
rustybin said:
Putting a cylinder head back on (BMW 523i) and didn't even get two of the bolts up to the jointing torque (40Nm) before it became apparent that they werent going in any further. Undoing them; same effect. Managed to remove the bolt and the thread has come with it. Any ideas how this could have happened? And probably more importantly: What the hell do I do now?
Sounds like these were buggered previously and have been helicoiled, which means putting in a new thread insert.
Don't sweat it, someone will be along soon totell you how to sort it out
Did you make sure that the threads were cleaned out?
i'm wondering if you've had oil or water down there which has caused a hydraulic lock causing the overload on the threads?
if it'd really fubar, i'd suggest getting it re tapped by an engineering firm, maybe a helicoil could be used as mentioned already.
i'm wondering if you've had oil or water down there which has caused a hydraulic lock causing the overload on the threads?
if it'd really fubar, i'd suggest getting it re tapped by an engineering firm, maybe a helicoil could be used as mentioned already.
Thanks guys, I don't feel quite such a moron now. I had cleaned the threads out very carefully as the head gasket blow had resulted in water and oil spread liberally around and into the threads so I don't think hydraulics was a problem. There doean't appear to be a helicoil in as the existing thread came out beautifully attached to the bolt (which looked like a rod when it came out.
To helicoil (or equivalent) the block, I assume I will need to drill slightly oversize. How can this be done accurately without taking the block out and to a machine shop. Or can't it.
Thanks for the advice guys, much appreciated.
To helicoil (or equivalent) the block, I assume I will need to drill slightly oversize. How can this be done accurately without taking the block out and to a machine shop. Or can't it.
Thanks for the advice guys, much appreciated.
One cause is using a bolt that's too long (or forgetting a washer - unlikely on a head bolt). You bottom the bolt, then it only takes about half a turn before the bolt rips the entire length of thread away, which then stays in the bolt helix as you describe.
You COULD repair it in situ, but you'd have to be bloody square with your drilling.
You COULD repair it in situ, but you'd have to be bloody square with your drilling.
Pretty sure the bolt is OK as the others are fine and they are OEM suuplied. My thinking so far with the drilling was to make (or more likely have made)a template out of 1/2" thick steel with three holes, two to accept bolts to locate the template on adjacent head bolt holes and one to act as a guide for the drill. A similar template could then be used to ensure that the tapping is straight.
Check first that you are able to get a repair kit of the correct size. If so, I think that if you were to use drillsof very slightly larger sizes, and increase the bore size in a few steps, then the drill should guide itself fairly well.
However, I have never drilled more than about M12 for recoil, and certainly not for any significant depth. I suggest you take advice from your local Auto Machinist. I have also been told that a mobile service is offered by some specialists (though not Auto Machinists), but I have never found any. If so, paying £50 or so for a mobile service is possibly your best bet.
However, I have never drilled more than about M12 for recoil, and certainly not for any significant depth. I suggest you take advice from your local Auto Machinist. I have also been told that a mobile service is offered by some specialists (though not Auto Machinists), but I have never found any. If so, paying £50 or so for a mobile service is possibly your best bet.
Get the repair kit.
It should come with a tap for the oversize thread, a number of coil inserts and the tool for fitting them. It should also tell you the size to drill. This is important so you would do well to buy the drill at the same time.
The size of hole you will drill is about the same size as the outside diameter of the existing bolt so the easiest way to make sure you drill the hole square is to drop the head back on and use that as you drill guide.
Fitting the insert is simple and should present no problems.
Don't beat yourself up over this as it is all to common. (Ask me how I know).
Steve
It should come with a tap for the oversize thread, a number of coil inserts and the tool for fitting them. It should also tell you the size to drill. This is important so you would do well to buy the drill at the same time.
The size of hole you will drill is about the same size as the outside diameter of the existing bolt so the easiest way to make sure you drill the hole square is to drop the head back on and use that as you drill guide.
Fitting the insert is simple and should present no problems.
Don't beat yourself up over this as it is all to common. (Ask me how I know).
Steve
I have tried finding one of the wandering thread repair guys but they seem somewhat thin on the ground and not too interested in private work. So I am taking the plunge and DIYing. An M10 recoil kit and additional longer inserts are on order. Fortunately I have a freind who is a tool maker so I will get him to make up a jig to get the drill and tap running straight.
Thanks again.
Thanks again.
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