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Rust blooms on any stainless cyclically loaded part should be a strong warning for two phases of degradation going on: 1. fatigue cracks and 2. crevice corrosion.
Fatigue endurance of most stainless steels is only approx. 1 million load cycles above 30% of the Ultimate Tensile values. Fatigue is 'additive' and may begin at stresses lower than 30%. Once the cracking begins crevice corrosion inevitably begins in the microcracks of the fatigue.
Id replace the bolts totally with 316 stainless, and then properly torque them down so that the whole mating 'surfaces' carries the load, not 'just the bolts'.
The chainplates should be examined very carefully for fatigue cracking (discoloration, surface rust, 'satinization' of the surface, etc.)... you can also remove them and perform some (Magnaflux) dye penetrant checking - exposed any invisible microcracks - most automotive machine shops can do Magnaflux type testing. Any area that the plates are 'bent' are usually high subject to microcracking, etc. Any plates that have done the equivalent of 'one circumnavigation' should be replaced.
Replacement plates should be flat sanded then mechanically 'mirror-polished' (follow by electropolishing if you have the extra $$$) to enhance fatigue endurance and corrosion resistance. Mill finish is 'not good enough' for chain plates, nor is any sharp edges, gouges, 'sharp' chamfers for the boltholes, deep scratches .... they should be 'perfect'/smooth/polished if you want them to last. I'd also get 316 St. Steel for the plates, preferably Stainless that is accompanied by documentation of strength, etc. (Mill Certifications) ... to avoid the 'asian crap' that is being sold for 'stainless'.
Last edited by RichH; 10-20-2009 at 02:17 PM.