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Old 03-21-2009, 11:40 AM
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2door 2door is offline
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Join Date: Sep 2008
Location: Littleton, Colorado
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Default Acorn vs. Hex Nuts

Somewhere in my early research about the Chinese engine kits I remember reading some disscussion about using hex nuts in place of the kit supplied acorn nuts on the cylinder head. There were some who maintained that the chrome acorn nuts would bottom out on the studs and therefore not allow proper torquing of the head. I've never removed the head on my first engine but neither have I had any issues with leaks at the head gasket or evidence that things have not remained tight after nearly 800 miles. Nevertheless, yesterday I removed the head on a new engine that I have yet to run. I was going to paint the head and polish the fins. Two acorn nuts came off easily, they had not been torqued from the factory, and two stayed tight to the stud and unscrewed them out of the block. When I held the studs in the vice to get the acorn nuts off I found them very tight and unscrewed hard all the way off. Examination revealed that they had bottomed out in the acorn nuts, damaging the top threads and consequently the threads inside the nut. I was able to run a die over the threads and restore them on the stud but I replaced all fours acorn nuts with shouldered hex nuts when I reassembled the head to the cylinder.
Now, after some thought I'd like opinions on this: Even if the acorn nuts bottom out, you'd still be able to torque properly IF, and here's the rub, if the studs are not bottomed out in the block.
IF, however they are, you'd stand the chance of doing real damage to the block, and, have a head gasket leak. Based on what I discovered I'd be inclined to suggest that this item be investigated on any new engine and/or those experiencing head gasket/compression issues. Just my observation.
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Last edited by 2door; 10-30-2009 at 05:29 PM.
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