Been redoing a DKZ engine out of a TZi and in the process of stripping down, had the ultimate nightmare happen; a headbolt sheared off. Nothing all that unusual you might say, heard of it before, but this was one with a bit of a difference; this one sheared off inside the block down at the thread with nothing protruding above the thread.
Worst part was, that this had obviously been corroding in there due to a very slightly leaking head gasket for a long time. Spoke to engine rebuilder/race car engineer friend who did all the machine work on the head and he advised white vinegar as a starter to be poured down the hole and left to soak. After a few days, we replaced this with Penetrene, then after a few days longer, added a small amount of engine oil and heated it.
Drilling it out was a daunting option as the holes the bolts pass through are tapered and being alloy, one slip with a drill and you're out the side of the block, so we turned up a sleeve, 55mm long by the diameter of the hole minus a 1.5mm taper with an 8mm hole through the centre. We then made another 60mm long by <8mm outside diameter with a 4 mm hole internally and sat the 8 followed by the 4 into the bolt hole. Using a special long 4mm bit, a pilot hole was (eventually) drilled through the centre; geez they're made of hard stuff, and then the inner sleeve was removed and an 8mm drill put through. A 9mm drill was ground incorrectly by giving it an exagerrated leading edge which caused it to grab the remnants of the shank of the bolt inside the thread and it then screwed out the bottom of the hole and was retrieved.
An old headbolt was slit on the emery to give it a couple of grooves and this was passed down all the threads to clean them out followed by another with oil being used to wash out all the threads.
Yesterday, we did the 60/20/300degree bit on all including the one that had the sheared off bolt in it and all went well.
Thought I'd pass this on in case anyone else strikes this and gets the same advice we did which was to go looking for another engine. This might have been more trouble, but at least we knew what we had.
Alan S
Sheared headbolt
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AlanS
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Sheared headbolt
By the time you're old enough to know it all, you can't remember why you were learning.
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Stewart (oily!)
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AlanS
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This one snapped about 2 threads into the block from what we could see as it was about 2 inches below the face of the block. At first I tried to run a drill down freehand but it was obvious it was running off. Then I tried to centre punch a starting mark but it had broken on such an angle even the centre punch wouldn't mark it, again just pinged off.
The 4mm drill I borrowed was made for drilling special materials and was sharpened in a special way to lower the chance of overheating and stuffing the end of it and it was over 4 inches long. The guy who lent it to me let me know in no uncertain terms that it had cost him A$48 so he didn't want it back in 2 pieces
and even it had big problems eventually biting into it.
The big trap is that without these sleeves we made up, it's almost a physical impossibility to keep the drill from taking the least line of resistence even if you could mechanically hold the block and the drill perfectly square due to the angle the bolt sheared on and the hardness of the metal along with the required length of the drill which causes it to flex.
It was one real hairy job I can tell you and I held my breath when I did the 300 degree stretch, waiting for the dull creak and the breaker bar going soft in my hands, but it held thank gawd.
Be interesting to now how many blocks have been scrapped for similar reasons.
Alan S
The 4mm drill I borrowed was made for drilling special materials and was sharpened in a special way to lower the chance of overheating and stuffing the end of it and it was over 4 inches long. The guy who lent it to me let me know in no uncertain terms that it had cost him A$48 so he didn't want it back in 2 pieces
and even it had big problems eventually biting into it.The big trap is that without these sleeves we made up, it's almost a physical impossibility to keep the drill from taking the least line of resistence even if you could mechanically hold the block and the drill perfectly square due to the angle the bolt sheared on and the hardness of the metal along with the required length of the drill which causes it to flex.
It was one real hairy job I can tell you and I held my breath when I did the 300 degree stretch, waiting for the dull creak and the breaker bar going soft in my hands, but it held thank gawd.
Be interesting to now how many blocks have been scrapped for similar reasons.
Alan S
By the time you're old enough to know it all, you can't remember why you were learning.
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docchevron
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We've just changed an engine in a ZX, ok, it was only a poxy XU5 monopoint thing, awful car, gutless as hell...
Anyhow, headbolt broke off some way below the top of the block, tried drilling it out, but found it to be impossible, although I must say we didn't try your method, maybe next time.. I ended up driving to Bridgwater to get another engine and the boys down the garage threw that in.
The block is still there, so I might just grab it and use it as "a practice" run, sooner or later I'm bound to bust a bolt off in one of the fleet..
Anyhow, headbolt broke off some way below the top of the block, tried drilling it out, but found it to be impossible, although I must say we didn't try your method, maybe next time.. I ended up driving to Bridgwater to get another engine and the boys down the garage threw that in.
The block is still there, so I might just grab it and use it as "a practice" run, sooner or later I'm bound to bust a bolt off in one of the fleet..
Smokes lots, because enough's enough already!
Far too many BX's, a bus, an ambulance a few trucks, not enough time and never enough cash...
Far too many BX's, a bus, an ambulance a few trucks, not enough time and never enough cash...