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Re: Want to Talk to Experienced Engine Rebuilder
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Posted by Chris-se-ILL on November 24, 2003 at 08:16:37 from (216.174.170.177):
In Reply to: Want to Talk to Experienced Engine Rebuilder posted by moonlite on November 23, 2003 at 16:31:13:
Well, you found an old crank-grinder! Back in '79 - 82 I worked in an automotive machine shop in Champaign, Ill. We did it all, including complete rebuilds (the engines were on stands, we did no "on vehicle" repairs) The myth of grinding past .020 is bunk! I have ground many cranks past the .030 in order to clean up the journals.... never had one come back! We used Sealed Power, Federal Mogul and Perfect Circle bearing books (still have some of those parts books) for guidelines on what was available in bearing sizes. We ground old tractor cranks (many for '49 and older pulling tractors, one year three tractors went to the State pulls in Springfield and won 1st, 2nd, and 3rd), and all types of truck and automobile cranks. Some of the cranks that were too large for our crank machine would be sent to "Effingham Regrinding" in Effingham Illinois (if you really want an answer to your question, call them. They are still in business!) As for the surface hardening... Yes cranks are surface hardened but according to most of the tech info that I ever read, most of the surface hardening was at least .070 to .100 deep (that is on a radius) Where as grinding .060 off the crank only removed .030 off the radius. We tried to not grind to .060 "because" it was such a pain in the backside (took too much time, we worked on commission). Plus, if a crank needed that much taken off it was usually due to burning a bearing (and extremely galling the crank) and if it was burned and galled bad enough to warrant turning that far... the crank was probably bent (twisted) anyway! So we usually recommended either sending it to Eff. Regrind. to be checked out (including magna-fluxing, straightening, and regrinding). The process of grinding a crank uses a "wet" grinding wheel and a stream of coolant on the journal as it is ground (cut). There is no loss of surface temper unless some operator tries to rush the grinding job and starts heating the journal face (which will take the temper out of the face). A machinist will use his ears to tell just how a cut is progressing (can tell instantly if there is a slight change in sound) along with watching the surface and using a special "swing-away" micrometer that is fastened right to the machine. The mic can be swung into position and will give a constant reading as metal is removed so that the cut will be accurate. I HAVE NEVER "heard" the stone change pitch as it would if it were to cut beyond the tempered face of the journal. And believe me, a machinist CAN tell by the "singing" of the wheel how it is cutting. As I said, we ground a lot of cranks, most between .020 and .040 (that is .010 to .020 on the radius) and some to the .060 size with NEVER a return. The shop had been in business since the late '30s. The shop closed it's doors sometime in the late '80s because it was bought out and liquidated by another company. A lot of that happened back then!
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