Subject	This is not about outright failure of head bolts
Posted by	LitlElvis on April 05, 2010 at 9:50 PM
	This message has been viewed 238 times.
In Reply To	Out of curiosity... posted by Obeeone on April 05, 2010 at 07:13 PM
Message	in service. The preload that can be induced into a fastener via torquing is directly related to the tensile strength of its material. The stronger its material, the more preload it can provide. Increased power means increased cylinder pressure, and at some point this pressure will exceed the fastener preload. when this happens, the bolts don't break, the cylinder head lifts or moves around a bit and the gasket gets pushed out. Put in a stronger fastener and the preload can be increased to hold everything in place for even higher pressures. This applies to the main cap bolts as well.
Follow Ups	Stock head bolt tensile tests >>> - LitlElvis 17:19:23 04/05/10 have you tested the replace ARP studs for reference? - Carlos Ramirez 17:37:15 04/05/10 ARP lists their standard 8740 studs to be 200ksi - LitlElvis 17:47:04 04/05/10 Interesting... - Gold300zx 17:38:36 04/05/10 I'm curious, was the breakpoint at the nut, or does it have - zellamay 17:53:55 04/05/10 it's more to do with the start of the threads - LitlElvis 21:37:58 04/05/10 To clarify, if the threaded portion was longer, and the - zellamay 21:59:16 04/05/10 it will break where the threads start to form on the shank - LitlElvis 22:05:54 04/05/10 Thanks, you have been very informative. (n/m) - zellamay 23:14:59 04/05/10 So the bolts dont really stretch? Just break.... (n/m) - ZXoltan 18:37:31 04/05/10 Yes they stretch - Brad(RI) 18:53:41 04/05/10 The threads are rolled. Like you, I hoped this would - LitlElvis 07:54:18 04/06/10 Out of curiosity... - Obeeone 19:13:36 04/05/10 Re: Out of curiosity... - Brett@AwesomeZ 19:31:20 04/05/10 Re: Re: Out of curiosity... - Brett@AwesomeZ 19:32:30 04/05/10 The graphs and some math tell the tale that you want to see - LitlElvis 22:03:39 04/05/10 This is not about outright failure of head bolts - LitlElvis 21:50:30 04/05/10 Never seen one issue with the factory head bolts yet (n/m) - Seb@Specialty-Z 22:36:43 04/05/10 Seb, what's the highest HP you have run with stock bolts? (n/m) - ZXoltan 07:45:11 04/06/10 a little over 1000 BHP (n/m) - Seb@Specialty-Z 10:12:31 04/06/10 Do you guys recommend the stock head gaskets or MLS styles? - KongZTT GT28RS MD 01:48:13 04/07/10 Exactly, it's not about breaking bolts - Brett@AwesomeZ 00:44:29 04/06/10 typically, fasteners are preloaded to 75% of yield strength - LitlElvis 07:16:53 04/06/10 I thought stock head bolts fell into this stretch category. (n/m) - Antihero 08:36:50 04/06/10 All fasteners stretch when preloaded, the key is to not - LitlElvis 11:56:01 04/06/10 the new ARP L19 hardware... - KongZTT GT28RS MD 01:54:07 04/07/10 You have an instron in your shop? Impressive! (n/m) - Scotts94z32 11:44:26 04/06/10 It's not mine, I just get access to it :-) (n/m) - LitlElvis 12:07:25 04/06/10 What adjustment factor do you apply to the steel>> - ZUL8TR 14:37:31 04/06/10 This is perfect.. I have been thinking of pulling - KongZTT GT28RS MD 01:41:27 04/07/10 err.. L19 (n/m) - KongZTT GT28RS MD 01:46:06 04/07/10
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