seems pretty logical. --- On Fri, 3/19/10, Greg Hermann <[email protected]> wrote:
From: Greg Hermann <[email protected]> Subject: Re: [alfa] Reusing head gaskets To: "ira kaufman" <[email protected]>, "alfa" <[email protected]> Date: Friday, March 19, 2010, 7:04 PM ira kaufman wrote: > if i may give an opinion.many head gasket failures i've repaired have had a > crack in the sealing ring.i'd venture to opine that after the many heatings > and coolings the metal in the sealing ring is tempered and can't reliably take > even the original torque let alone an increase without cracking. > > The sealing rings are generally made of an austenitic stainless steel alloy, and as such are NOT subject to tempering in the manner which you imply might occur. Further--although it doesn't really apply here--getting a metal hot generally tends to anneal it--and thus reduce any tendency to crack due to the presence of any strain hardening. Not to deny that the cracking you have observed doesn't occur, it does, I've seen it much as you have. Such cracking is generally the result of 'fatigue'--too many cycles at too high a level of stress. If stress stays below the so called 'endurance limit' of a metal part, then it will not crack and fail. It generally takes between eight and twelve MILLION stress cycles at a given level with no failure before it is established that a metal is not being stressed beyond its endurance limit. Needless to say--you ain't gonna get even into the neighborhood of that many cycles torquing and re-torquing a head. What WILL get you there is the number of pressure rises due to combustion events the gasket ring experiences in an operating engine. What generally WILL cause the observed cracking is too LITTLE clamping force on the sealing ring--generally as a result of inadequate torquing of the head fasteners, inadequate clamping force due to failure to lube said fasteners prior to torquing them, improper height of the liners relative to the block deck, and/or improper (or non-existent) torquing of the head fasteners as an engine warms up for the first time. In plainer language--if there is adequate clamping force between the head and the top of the liners, the friction between the sealing ring and the head and liners acts to reduce the (varying) radial stress on the sealing ring sufficiently to prevent it from fatiguing and failing. Greg -- to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi or email "unsubscribe alfa" to [email protected] -- to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi or email "unsubscribe alfa" to [email protected]
