258 head bolt help - 7/16 head, 1/2" block - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 06-30-2001, 03:27 PM Thread Starter
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258 head bolt help - 7/16 head, 1/2\" block

I had the head from an 84 258 rebuilt and was ready to bolt it on to my 80 block this morning and realized when I went to insert the first head bolt that my block has 1/2" diameter head bolts. After a few minutes of cussing I decided to drill out the head to accept the larger diameter bolts that fit the block. Drilled em out and went to bolt it together, and now I find out that the 1/2" bolts off the 80 block are longer and bottom out before I can torque down the head.

So now I need 1/2" head bolts that are about 3/4" shorter than what I have. The head bolts are marked with six lines (grade 8?). Can I just go to my local supplier of fasteners and use grade 8 bolts of the right length? Any suggestions welcome!

The bolt to make this work needs to be about 3 3/4 long with 1/2" course thread.


84 CJ7, 258, HEI, M/C 2100 carb, 5 inch lift, RS9000's, 33x12.5 BFG M/T's, Lockright, full cage & belts, Xenon flares, AMC 20 1pc axles, GM dual diaphragm brake booster
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post #2 of (permalink) Old 06-30-2001, 06:48 PM
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Re: 258 head bolt help - 7/16 head, 1/2\" block

I would want to be sure to have flange head bolts. Maybe it's not so necessary, but it would seem like the flange of a head bolt would help greatly when you're trying to accurately trying to torque the head. Me, I'd pester one of the guys at napa to find a vehicle that uses that size head bolt. That flange seems important, but I don't have a fastener store. Maybe they carry that style bolt? Anyhow, those are my feelings. Best of luck to you. Brendan

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post #3 of (permalink) Old 06-30-2001, 07:40 PM
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Re: 258 head bolt help - 7/16 head, 1/2\" block

i believe HESCO sells the correct bolt for this conversion!

try them at: http://www.hescosc.com/

good luck!

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post #4 of (permalink) Old 06-30-2001, 07:44 PM
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Re: 258 head bolt help - 7/16 head, 1/2\" block

The six marks do mean it is grade 8 hardware. If you have a good fastener shop or industrial supply shop they should be able to fix you up. Just be prepared to pay more than you think they are worth. I just had to pay $13 for 4 3/8 inch bolts at Clarksville Fasteners.

post #5 of (permalink) Old 06-30-2001, 11:01 PM
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Re: 258 head bolt help - 7/16 head, 1/2\" block

I compared my old 258 head bolts to some from my local (great) fastener outfit and couldn't tell the difference from one to another.
These relacments even had a slight shoulder just below the hex ... just like the stock ones.

BTW: I sure hope you at least used a drill press and very carefully aligned the 1/2" bit center over the 7/16" holes ... skewed and/or off center bores will really screw up your torque uniformity ... and that can lead to warps, leaks, etc, ... [img]/wwwthreads_images/icons/shocked.gif[/img]

That '80 block is a prime candidate for a 4.0 head swap!!!

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