# '64 389 head bolt length



## 64since65 (Dec 11, 2019)

I have a few questions today but I'll keep them separate for clarity.

I'm about to put the heads back on my engine but not sure what to do with the head bolts. I bought a new set of bolts under the assumption that I should use new ones. However, the longest 6 bolts on my engine were 4-1/4" and the longest I could find in new ones was 4". When I put all the bolts in with the heads sitting on the bench, the amount of thread showing is obviously less for those 4" bolts than any of the others. The 4" bolt only has about 3/8" of thread engagement vs. 5/8" engagement for the 4-1/4" bolts. I'm not sure 3/8" engagement is enough for a 1/2" bolt.

So the question is, can I re-use the old bolts (which would mean I wasted a lot of money on new bolts) or should I keep looking for a source of 4-1/4" head bolts? If I need new ones, does anyone know where I can get some? (I've tried OPGI, Ames, Summit, and Butler and didn't find anything over 4" but haven't called to check yet either. I'm a bit surprised that all of them only go to 4" when my originals are obviously longer.)


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## Old Man Taylor (May 9, 2011)

Yes you can use the old bolts. I've reused them many times.


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## 64since65 (Dec 11, 2019)

EXCELLENT! Thank you!


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## BearGFR (Aug 25, 2008)

Or, if you want new ones you can measure the lengths of each one and either get a set from ARP, or buy individual bolts by length. With the head sitting on the deck, drop the bolts in. The head of each bolt needs to sit an inch above the head/washer. Trying to torque down a bolt that's too short can pull the threads out of the block. 

Bear


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## 64since65 (Dec 11, 2019)

Yeah, a full inch would be better but, for the benefit of others reading this, I put a bolt in a few of the holes in the block (without the head in place) and they became finger tight at about 3/4 inch. So they'd never tighten if they sit up a full inch. The old bolts will go about 5/8" into the block and the engine had about 150,000 miles on it when I took it apart so that must be enough for this engine. That's not to say that a full inch wouldn't be better; I just don't want someone else to panic because they can't get a full inch or buy bolts to give them a full inch and find out they won't fit - check first. However, I would be was worried when my new 1/2" bolt didn't even engage 1/2" of thread - which is a common rule-of-thumb minimum.


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