Re: Want to Talk to Experienced Engine Rebuilder

Posted by Hoosierbuddy on November 24, 2003 at 07:33:35 from (67.241.18.17):

In Reply to: Want to Talk to Experienced Engine Rebuilder posted by moonlite on November 23, 2003 at 16:18:40:

When a crank is ground it simply removes the hardened portion of the crank-thus dramaticly shortening its life.I would have it re-hardened if I were turning/grinding it-but my experience has been with high powered Warbird engines.

The hardening of components is an important step in manufacturing mechanical components. The principle of hardening is to induce residual
compressive stresses in the material, which increase the critical load at which cracks will occur. Different techniques are used in the process. These include shot-peening, work hardening, ion-nitriding or ion-implantation, laser and induction hardening and deep rolling.

If extreme durability is the goal, you might talk to your machinist about nitriding. This process case hardens the crank to a depth of .020" or .030", without affecting the characteristics of the base metal. Surface hardness doubles from 30 or 35 Rockwell C to 60. This technology was primarily limited to military and commercial aircraft until the 1960s when Chevrolet specified nitrided crankshafts for the 327 Corvette. "Tufftrided" crankshafts were also installed in extreme-duty Chevrolet truck engines. The largest users of such crankshafts today are Mercedes-Benz, Perkins Diesel and Honda.

Nitriding iron can be done in several methods. The old process where the metal is soaked in a "Salt Bath Ferritic Nitrocarburizing" solution for a required period of time to increase fatigue strengthed is one method. The level of strengthening is directly related to the amount and in what form nitrogen occurs. The cost of hardening a crankshaft using this process is about $200, where most of the cost is concentrated on disposing of the solution once the hardening process has been completed.

The grey, sometimes almost black nitrided cranks encountered today were heated in an oven to 950° F in the presence of gaseous nitrogen.

Light grey cranks were subjected to ion nitriding, a process that uses microwaves for heat generation. The cost is similar to the salt bath method.
Anyone remember that IH used to advertise the "Tocco Hardened" crankshaft?
HB

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