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Discussion Starter #1 (Edited)
I removed the Original 049 Heads, and had them rebuilt, ang when I was cleaning the block head bolt holes, I noticed the Tap on one hole stopped about 5 thread turns like it bottomed out after looking I took a pic this is what I found. Should I drill it out and retap . It never leaked or lost water. If I need to drill it what size drill and where will the shavings end up.Thanks for help Also I looked at the bolts I removed which were ARP none were broken..
 

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I've had good success in removing part head bolts down hole using a 7/16" UNC threaded rod about 1-1/8" long, drilled through the exact center using a lathe, size 1/4". Then fit the threaded rod into the remaining threads, I then use a LH cut 1/4" HSS drill bit to drill into the broke head bolt piece. The head bolts are made of high tensile steel, so the drill bit needs to be slower, use oil to cool it while drilling. Drill into the broken piece about 1/4" then remove the threaded mandrel. Continue drilling using the LH bit, usually the drilling friction is enough to wind the broken piece out.
If it doesn't come out with the LH drilling, and you make it right through, use an easiout extractor to remove the broken piece, be carefull, it didn't break for no reason so if there is resistance take care or you may break the easiout, then you have bigger problems.
 

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Discussion Starter #3
looks like it has already been drilled out.it looks like this is the side of the bolt that had broken off. I put a small long screw driver and it went pretty far down past the sides where the Tap stops
 

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you removed bolts? i guess i don`t see the problem. the head of the bolt bottomed out against the head, right?
 

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Discussion Starter #5 (Edited)
I guess it did they were all tight and still had the ARP thread sealant on the bolts. It is the outside bolts the smaller ones the one by the motor mount boss on the passenger side.It is about 5 threads down in the hole.where the Tap stopped. I guess I will install the head and see if that bolt will torque ok.
 

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This almost sounds like someone removed a broken bolt before you came on scene, and they drilled too deep. Maybe into the water jacket. Too repair they used an allen head stud. Probably with thread locker.
Maybe get a look closer with a borosope to spot the hex socket?
 

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Discussion Starter #8
the engine I purchased about 2 years ago out of a 73 chevy 3/4 ton pick up, It ran fine and we pulled it and I installed it in my 55 hooked it up ran fine, I just figured I would have the heads rebuilt since I changed to a roller cam set up , and was just chasing the threads and this is what I found. all the rest of the holes the Tap went all the way down but not this hole, I will do what you said but when I installed the long small screwdriver it went far down like the rest of the holes. So the center of what ever it is looks to have been drilled out
 

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i still don`t get it? you removed the bolt? and yes, looks like a heli-coil. so are you saying only half a bolt came out?
 

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Discussion Starter #10
when I removed the heads to take to the machine shop all the ARP bolts that came out were all torqued down none were broken ,when I went to clean the threads in the block I found this one hole and I figured at some time a head bolt was broken and someone drilled it out but it didn't all come out only one side of the bolt or whatever it is helicoil is still there. I don't think it hinders the bolt from torquing down
 

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as long as the bolt threads in far enough to clamp the head down and not bottom out it is fine. once in a while there is core shift during the casting process and the wall is thick near the deck. when the machine drills the holes it only drills so far and leave a buttress at the bottom of the hole. as long as it is deep enough it is fine. also check the head bolts to see if one has been shortened??
 

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Measure the thickness of the head @ that bolt location, add the thickness of the head gasket. Leave the head off & screw the bolt in the subject hole by hand.
Measure from the deck to the underside of the bolt head.
If the length of the protruding bolt is less than your head / gasket measurement your good to go. If no add a cut washer to the bolt or trim a few threads off the bottom.
 

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"churchkey" got it right! i stripped the threads in a 327 years ago, i just drilled it out, heli-coiled, running strong yet. no machine shop, got out my drill, did it in the garage by hand.
 
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