Acorn vs. Hex Nuts

[2door]

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.
Tom

[2door]

I'm bumping this very old thread because I just finished building a new motor and I encountered the same problem on it as I've found on several others previously. That being that the factory supplied acorn nuts were bottomed out on the studs. That in itself might not cause a problem but something else I've discovered is an inconsistency in stud length. I've compared them in several engines and found a variance of over a quarter inch in length. A longer stud could bottom out in the engine case and if the acorn nut also bottoms out before proper contact with the cylinder head then that stud/nut is not doing its job. I have to wonder if this is not the reason for some blown head gaskets and compression loss experienced by some. Just a thought. I always replace the kit supplied acorn nuts with hex nuts on the cylinder head/studs and the studs and nuts at the intake and exhaust with Allen head cap screws because if this problem. Any comments?
Tom

[taddthewadd]

I have learned to check the torque on all hardware in a new kit. On my last kit half of the screws on the engine were loose. I also replace the acorn nuts with regular nuts right away that way I can sleep at night :-)

[Kevron99]

I bought 2 chinas already and all with loose acorns. I will always replace the acorn.

[Cabinfever1977]

I have acorn nuts on my head,(lol that does sound funny) but any way when i first was breaking in my engine i noticed a little oil residue near the head gasket and tighten the acorn nuts using very little pressure, and they stayed tight and leak free for 1,300miles now.

[mountain80]

I replaced the acorn nuts with hardened 8mm nuts and washers along with the studs which are grade 12.8 . Never had a single problem since.

[Pablo]

Acorn nuts are junk. Use them in your next concrete pour.

[Creative Engineering]

Originally Posted by Pablo

Acorn nuts are junk. Use them in your next concrete pour.

Good grief!

Acorn, or cap, nuts have been around for a long time. I certainly hope they aren't junk! Motorcycles, autos, aircraft, all use acorn nuts. Acorn nuts aren't different...they simply have a closed crown that covers the exposed end of the threads.

They are used to:

1) To protect the threads from damage/corrosion/dirt.

2) To protect skin from the sharp exposed threads.

3) To create a clean, finished, appearance.

The problem comes from the length of the threaded portion that the nut engages. Obviously if the stud length is not correct, the Acorn nut will bottom out before it clamps the mating parts.

I'll agree that, (for most MB'ers), it's easier to replace the acorn nuts with standard hex nuts as opposed to correcting the length of the stud.

Jim

[Pablo]

OK I wasn't specific. THE CHINESE SUPPLIED BIKE KIT acorn nuts USED for the HEAD studs are a JUNK IDEA - Use them in your next concrete pour.

In and of themselves acorn nuts are not bad. They are just not what to use for any head stud, unless you leave some exposed stud thread and use them for decorative caps.

If you are interested in properly torquing your head nuts, throw away (or set aside!) the acorn nuts and use a proper torque wrench and good hex nuts.

So in closing, throw away the BIKE KIT acorn nuts. Use them in your next concrete pour. Following this is very sound advice and will prevent stripped studs. No need to get all high and mighty about it.

[jeffhalfrack]

Hey Pablo what's that avatar???????????? scorpa trials bicycle??? I have a scorpa easy .250 I'm looking to sell. I'd love to see a bigger pic of what ever it is JW