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Old 07-10-2009, 11:06 PM
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400 sbc Head Bolt Broke

So... I was re-assembling my SBC tonight and was following the correct torque sequence and torque with a calibrated (took it from the lab at work) torque wrench when I snapped a head bolt off. Now I need to somehow remove the broken stud in the block... there is minimal thread sticking above the deck so I won't be able to use vice grips... what should I do? The hole that the stud broke off in was the one right next to a steam hole and I noticed a small hairline crack from the threaded hole to the steam hole... how severe is this?

Any help would be appreciated... I've got a lot invested in this problem proned engine. Thanks for any help or suggestions (I hope the block isn't junk).

-Luke

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Old 07-11-2009, 10:53 AM
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Check out this thread.
400 SBC Steam Hole Crack

Since the threads go all the way through the block`s deck, you should be able to use a sharp point chisel and ease the broken bolt out with light taps with a hammer. Lube up the bolt good prior to starting.
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Old 07-11-2009, 11:03 AM
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Hi,
You can use a small punch or chisel & tap it out,
that is use the tool & hammer to make an indention in the bolt
& then continue tapping the tool in the indention with the hammer, the stud should back out.
Rich
Why do you think this bolt broke?

Last edited by richard stewart 3rd; 07-11-2009 at 11:11 AM.
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Old 07-11-2009, 11:20 AM
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broken bolt removal...

Hi,i would put a nut,about the same size as the broken bolt, over the bolt, and weld the nut to the bolt. thru the hole in the nut, weld it good. then before trying to remove the broken bolt,spray it with PB Blaster.2 or 3 times,let it sit overnite, then turn the bolt out.sorry,cant help you out with the crack,i would have to see the crack first.
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Old 07-11-2009, 11:24 AM
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Hi Bob,
That's a good tip, Thanks.
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Old 07-11-2009, 12:42 PM
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Thanks guys, I just went down and bought some new Head bolts and will try backing the stud out using the punch/hammer method. I'm worried about welding it because of the heat concentration in the area (bolt broke in between cylinders).

Thanks for all of the input! I'll let you know how it turns out.
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Old 07-11-2009, 01:27 PM
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There's no way to convey over the 'net how much it takes to torque a head bolt, but the amount of torque to cause a GOOD bolt to fail, is considerable.

If the wrench you're using has you straining to reach the head bolt torque setting (65 ft/lb), stop using it and try to find another wrench. 65 ft/lb is tight, but not THAT tight, for lack of a better way to describe it.
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Old 07-11-2009, 03:32 PM
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Weirdly I understand what you are talking about... The failure occured on the final torque of all the bolts (25, 50, and then 65). I felt that it was close to the final torque when all of a sudden it became easy to turn for half a turn and failed.

If I recall correctly from my days in college, the proper way to design a 'bolted joint' is to understand the material and diameter and then calling out a torque that is 75% of the yield point. My guess is that I've used these bolts too many times, fatiguing the bolt, causing a degregation of the bolts elasticity. This was the second head I was torquing and I believe I have some suspect bolts on the other side as well so I'm going to replace them all with the new bolts.

Do you think I can reuse the head gasket that was 'somewhat' torqued down? It looks fine, however, it was evenly torqued to 50 ft lbs. before the bolt failed.
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Old 07-11-2009, 05:04 PM
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i think i would go with the welding of the nut idea. I think that would be the best way to go. Three letters I like to hear about and engine ARP.
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Old 07-11-2009, 05:28 PM
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You also can try to drill a hole down the middle with a 1/4" left handed drill bit, drill down into it about a half inch if it does not spin out. Then use an easy out.
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Old 07-11-2009, 07:07 PM
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just don't break the easy out off in the bolt otherwise you would have even a worse mess trying to get that hardened easy out of the inside of the bolt
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Old 07-12-2009, 12:49 AM
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If drilling it did not work then you could try welding nut to top of bolt. I always hated welding on something you are trying to keep clean and all those welding bb's that go every where if weld pops throwing bb's every where in new motor the welding blankets full of bb's. Mack off area with some 2 inch macking take and drill if you have a good tap handle you can tell if easy out is not going to work. The only way this bolt is going to be a pain is if it is bottemed out against some thing
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Old 07-12-2009, 12:57 PM
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lets look at this a smarter way first. Give your local machine shop a call and tell them your situation and see if they can extract that bolt for you. Hell they might only charge you 20 bucks to extract the damned thing.
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Old 07-12-2009, 05:35 PM
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Guys thanks for all of the input, it turned out to be easier than I thought. I called up my local machine shop guy, and he suggested before I bring it in to just give it a light tap with a punch (like some already suggested) and wouldn't you know, it backed right out. Following this 'key learning' I chased the threads and installed new head bolts. Everything seems to be a go! now I just have to get the rest of the chasis ready

THANKS AGAIN FOR THE INPUT AND HELP!
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Old 07-12-2009, 05:49 PM
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Quote:
Originally Posted by manchildau65
Do you think I can reuse the head gasket that was 'somewhat' torqued down? It looks fine, however, it was evenly torqued to 50 ft lbs. before the bolt failed.
Personally, I would have no problem trusting the gasket - I would reuse it w/o hesitation.
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