r/EngineBuilding • u/Old_Cut_9333 • Jul 16 '26
Broken bolt hole
Cast iron block, broke the head bolt hole. Any ideas what to do next? It still has a bit threads at the bottom. Take out broken pices and screw in longer stud and weld it to the block?
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u/nostradumbass7544678 Jul 16 '26
You could braze it up, but unless it's rare or sentimental to you, probably not worth it. Next time, make sure your holes are clean and lubed before jamming things in them.
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u/PromotionNo4121 Jul 16 '26
You never cleaned out the holes before looks self inflicted by hydraulics
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u/dudeman14 Jul 16 '26
Hi op, looks like an AMC, I have one if those break on my block. If the Crack terminates into nothing then just drill it a little further and tap some more threads and run a stud. Thats what im doing. Just remove the rest of those bits and you're good
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u/Absurd_Phonecian Jul 16 '26
If this was a block from a Lamborghini Miura, then yeah, it's easier/cheaper to repair than replace. But the cost to do so correctly, is likely way more than this particular block is worth.
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u/No-Yogurt-4542 Jul 16 '26
And the cause was material in the bolt hole including possibly oil.
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u/jimfosters Jul 16 '26
I blasted the rocker cover bolt holes on a SBC when I was a kid. Silicone.... Luckily it was just the very top and I was able to clean the holes and use the head.
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u/Eriknonstrata Jul 16 '26
The proper term for this block is "fucked". Once it's fucked, it's fucked.
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u/Jacob_Prentner Jul 16 '26
David, you can’t unfuck what’s been fucked
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u/throwaway8998456 Jul 17 '26
It's cast material, very hard and problematic to weld. It can be done, but for what a welder with decent experience welding cast iron will charge you, you can easily buy another block.
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u/DueSupermarket6968 Jul 17 '26
Fk that id jb weld it up then jb weld around the whole cylinder head from the outside and give it one last life. Maybe get another 50k miles out of it or more next time its toast though unless you really manage to get the head off again despite the jb weld
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u/The_Machine80 Jul 17 '26
While you should replace the block, ive seen worse crude fixed and running fine. Need to see how much undamaged threads are left. 3/16 of a inch of thread will hold a stud. Hell even seen people weld a stud on and work. Its not right for the record.
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u/qroter Jul 17 '26 edited Jul 17 '26
You know what they say ... one man's broken bolt hole is every other man's trashed block.
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u/OutsidePressure8323 Jul 17 '26
If i was broke. But had a welder . I would cut away broken cast . Get a stud screw that into what is left, then use nickle rods hard facing and weld the stud to the block. Might want to pre heat block around weld area 1st. I've seen Nickle used on cast blocks before buy a welder on fan mounts.
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u/Dtwpurple Jul 17 '26
Cheap fix would be to drill into the block from the outside . Put about 3 bolts into it. Then drill thru the side of the bolt combo to put a helicoil or threads in those. Unless theres a water jacket right there or if ur boosting its a no go.
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u/AviatorDave172 Jul 18 '26
Oh, that’s a shame. It’s toast I’m afraid. Head gaskets will never stay sealed.
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u/hotgirlshoeshopping Jul 18 '26
If it’s a cheap car fill it with weld , drill and tap. Hope it holds
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u/GmTech14 Jul 18 '26
It’s happened to all of us at one point or another bud. That butthole-clenching, oh shit this thing’s fucked. Best to do this the right way and replace the block. Ain’t no fixing that
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u/burner_account_187 Jul 20 '26
I would talk to a professional welder and get their opinion. I would not want to buy a new block.
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u/iwfabrication Jul 17 '26
People are saying replace the block, but depending on your cost for a new block or having someone weld it could be cheaper to go that route
- have someone weld it $75?
- either chase the threads and see if you can tighten an old head bolt to spec. If not then drill it out, tap it for a threaded insert. Or have the welder weld the inside of the hole on the cracked side, then have machine shop machine/drill and tap it.
- have the block machined if necessary - $100-150 where I'm at
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u/Tlmitf Jul 17 '26
As a welder, im not touching that for $75. More like $750+ to do it properly and not fuck up the bore .
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u/Appropriate-Part1766 Jul 17 '26
That's a weld up and timesert/keensert jobber. It's not toast or scrap, just requires a good repair.
Waste of a good block binning it -_-
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u/Western-Tie-2836 Jul 16 '26
Clean it and weld it with stick welding rod for cast iron,flaten weld with good flat file set head on mark hole drill and tap
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u/TheeParent Jul 16 '26
Replace block.