Re: Re: Want to Talk to Experienced Engine Rebuild

Posted by Chris-se-ILL on November 29, 2003 at 06:55:21 from (216.174.170.190):

In Reply to: Re: Want to Talk to Experienced Engine Rebuilder posted by Mr. Goodwrench on November 24, 2003 at 20:15:24:

It would seem that you still believe that grinding .060 undersize (taking .030 off of the radius of a crankshaft) will weaken the design and strength of the crankshaft to the point of breakage. If that .030 of flame hardened metal (less than the width of the gap of most sparkplugs) along the outside edge of the journal, is all that is keeping a crankshaft from breaking at the maximum torque upon the crankshaft (in other words the tolerances are so close, at that point of removing material, that the allowable safety margins are negligable)... well that just impresses the crap out of me! That is some strong .030 of metal!!!

And to think... I thought that just the outer surface of the crank was hardened (usually somewhere near .100 thick on the radius) in order to resist the abrasive wear from contaminants in the oil. Now I learn that it is hardened to resist the inherent torque of the engine. If the designers needed strength from hardening the crank... then why didn't they just harden the entire radius of the metal (hardened to the core of the crank)? Maybe it is because they want some "flex" to the crankshaft so it won't break from the torque stresses.

I believe that there are folks like you that believe that the hardening (tempering) of the surface (bearing face) of the journals is for the purpose of extra torque strength (strength against twist). In my opinion, your belief of such... is a falacy! It makes almost no design sense to just harden the bearing surface area to add strength against torque! Especially since there is no "surface hardening" on any other part of the crank except the bearing faces... the webbing and connective material between the journals usually have no surface hardening whatsoever! They are usually just rough cast!

It does however make sense to temper the bearing surface area in order to resist errant abrasion from particulates in the lubricant!

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