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Discussion Starter · #1 ·
Coming home from a car show Saturday I heard an engine noise a felt a vibration. After I got home I lifted the hood and heard what sounded like a rod knocking but turned out to be a loose balancer upon inspection. The bolt broke and fell off and the fan kicked it up on the alternator bracket.
The problem is the bolt broke off about 1/2 inch up in the crankshaft. It is not loose enough to be turned out with a scribe or pick.
After talking to some friends we figure my best bet is to make a pilot bolt with a hole drilled through the center for a drill bit to go through. Screw the bolt into the crank as far as possible and drill through the pilot bolt into the broken bolt.
The thinking is to keep the drill bit centered and to stay off the crank threads.
Any thought on this problem may be a big help to me.:1zhelp:
 

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Cocke County, TN. 55 Bel Air Sport Coupe
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Maybe just pull the balancer then unscrew what is left of the bolt?

Coming home from a car show Saturday I heard an engine noise a felt a vibration. After I got home I lifted the hood and heard what sounded like a rod knocking but turned out to be a loose balancer upon inspection. The bolt broke and fell off and the fan kicked it up on the alternator bracket.
The problem is the bolt broke off about 1/2 inch up in the crankshaft. It is not loose enough to be turned out with a scribe or pick.
After talking to some friends we figure my best bet is to make a pilot bolt with a hole drilled through the center for a drill bit to go through. Screw the bolt into the crank as far as possible and drill through the pilot bolt into the broken bolt.
The thinking is to keep the drill bit centered and to stay off the crank threads.
Any thought on this problem may be a big help to me.:1zhelp:
 

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Coming home from a car show Saturday I heard an engine noise a felt a vibration. After I got home I lifted the hood and heard what sounded like a rod knocking but turned out to be a loose balancer upon inspection. The bolt broke and fell off and the fan kicked it up on the alternator bracket.
The problem is the bolt broke off about 1/2 inch up in the crankshaft. It is not loose enough to be turned out with a scribe or pick.
After talking to some friends we figure my best bet is to make a pilot bolt with a hole drilled through the center for a drill bit to go through. Screw the bolt into the crank as far as possible and drill through the pilot bolt into the broken bolt.
The thinking is to keep the drill bit centered and to stay off the crank threads.
Any thought on this problem may be a big help to me.:1zhelp:
That sound like a good plan to me. I have to say I never seen a crankshaft bolt break that way. Sounds like bolt could have bottom out when installed. or was the wrong kind of bolt. If so it may be real hard to get out. You may have to find a way to but some heat on it to get it out.
:anim_25:
 

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Another trick, if the bolt ISN'T bottomed out and twisted off is to use a left hand drill when you do your drilling. Instead of trying to spin the bolt further in the threads, it tries to unscrew the bolt which can be helpful. If it's jammed, don't spend the extra money.
 

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+ 2 on the pilot bolt plan, a couple of thoughts I have are, maybe; use a reverse twist drill bit to avoid tightening the broken bolt further into the snout, tighten the pilot bolt against a nut to keep it square and concentric, instead of against the broken bolt which might tilt the pilot bolt in the hole (the broken bolt probably doesn't have a square end), dull the threads on the drill shank where it goes through the pilot bolt, and maybe even use bronze or brass for the pilot bolt to reduce friction and heat buildup.
Is your drill press setup capable of making a perfectly centered pilot bolt?
Mine sure isn't, and that would be important for success in what I consider a nightmare job, I really don't envy you here.
Maybe I'm just paranoid... Good luck!!

Hey speedbump, you're a speedier poster than me!
Another thought, I got one of those $30 ARP 12 point bolts, might be a good investment.
 

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You need to drill a hole to use an extractor, so all the hole drilling comments apply.

I like the idea of the "pilot bolt". However, it's likely that there is nothing to thread into, so in that case it's just a pilot drill bushing.

I would try the left hand drill bit when drilling. If the broken bolt turns, you've accomplished your job. If it drills, then proceed to an extractor.

I know the broken bolt is not out yet, but it's time to be thinking about why this happened and how to prevent it. There should be no significant load on the bolt unless something else went wrong. Like a bad pulley, cracked hub for the balancer, etc. So be studying the parts as they come off for clues as to what went wrong. Keep in mind that most Chevy V8's didn't even have a bolt there through the 50s and 60s, and some didn't even after that.
 

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Discussion Starter · #8 ·
One of my buddies has a lathe for getting the hole in the bolt centered as I also believe that to be critical and he is doing that tonight.
I do plan to use left hand drill bits and plan to increase the size of the hole once it s drilled. Hopefully the bolt will come out as the hole size increases.
I didn't build the motor so I can't say if it bottomed out but I sure hope not.
From the looks of the bolt it seems to be an old break with only a small corner on the break being shinny. It dose not look like a grade eight bolt as I don't see the normal 6 marks on it so maybe that's the root of it all.
Thanks for the interest.
 

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I think you are on the right track with the bolt idea. Couple of years ago my son was installing a new cam in his 55 . Good old dad thought he would help and yes we may have been drinking beer.......... But I twisted the bolt off using an impact wrench. I said son of a gun and felt pretty bad about it. Drilled it out and stopped by Speedway Motors and asked for a replacement bolt for the Small block. They gladly sold me a ARP bolt for 29.00 plus tax. I thanked them and moved on.
Long story short you can get it out , good luck with your project.:anim_25:
 

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Discussion Starter · #10 · (Edited)



Success! all went as planned. The broken bolt has ben removed. I've posted 3 pictures, two show the broken bolt. One pic shows the pilot bolt that I used to drill the first hole with.
 

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What's the bolt thread engagement? Is it long enough? Looks like it may have been short.

I am a firm believer in maximizing the thread engagement on this bolt. The old B&B bolts I used to use were purposely sold too long - you had to shorten them every time. But you have to make absolutely sure that the bolt isn't bottoming out either.
 

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Discussion Starter · #13 · (Edited)
What's the bolt thread engagement? Is it long enough? Looks like it may have been short.

I am a firm believer in maximizing the thread engagement on this bolt. The old B&B bolts I used to use were purposely sold too long - you had to shorten them every time. But you have to make absolutely sure that the bolt isn't bottoming out either.
You are correct. I think the bolt is 1/2" short. The rule I've always observed is 1 and 1/2 times the diameter of the bolt for for all fasteners. The bolt is a 7/16 but only about 1/2" engagement.
The bolt was two inches long (including the broken off part ) and if you look closely you can see the buggered-up threads it which happened after it broke I think.
 

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You are correct. I think the bolt is 1/2" short. The rule I've always observed is 1 and 1/2 times the diameter of the bolt for for all fasteners.
2 diameters is even better if there is room for the extra length.
 
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