ZR-1 Net Registry Forums - View Single Post

A26B · 10-08-2008

I'm going to share a conversation I had with Graham Behan last May about this subject.

As I recall, Graham said they never actually measured the bolt length when installed, cold or hot. Due to the higher thermal coefficient of expansion, aluminum vs steel, the bolts will incur higher axial tension at engine operating temps than when installed at ambient conditions. Determining the difference in length would require flat grinding the ends of the bolt and using a sonic instrument to measure the differential length, cold to hot. With that information, stress on the bolt can be calculated to see if yield strength was exceeded. It could also be obtained by accurately measuring the length of a new bolt at std temp with a micrometer before install and again after it was removed from a heat cycled engine. If the length is greater after use, that would be an indicator of permanent deformation, and therefore exceeding yield strength of the bolt.

I came away with the impression that replacing the bolts after 1 use was an insurance policy factor as opposed to empirical testing data.

Would be interesting to know about head replacements with used bolts & the results.

Jerry

10-08-2008	#13
A26B Join Date: Dec 2003 Location: Arcadia, OK Posts: 3,403	Re: Engine Parts I'm going to share a conversation I had with Graham Behan last May about this subject. As I recall, Graham said they never actually measured the bolt length when installed, cold or hot. Due to the higher thermal coefficient of expansion, aluminum vs steel, the bolts will incur higher axial tension at engine operating temps than when installed at ambient conditions. Determining the difference in length would require flat grinding the ends of the bolt and using a sonic instrument to measure the differential length, cold to hot. With that information, stress on the bolt can be calculated to see if yield strength was exceeded. It could also be obtained by accurately measuring the length of a new bolt at std temp with a micrometer before install and again after it was removed from a heat cycled engine. If the length is greater after use, that would be an indicator of permanent deformation, and therefore exceeding yield strength of the bolt. I came away with the impression that replacing the bolts after 1 use was an insurance policy factor as opposed to empirical testing data. Would be interesting to know about head replacements with used bolts & the results. Jerry __________________ Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 *ZR-1*, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed.