11/1/2002
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Learning Curve
After Three Fun Years It’s Time To Pass The Baton
By Clarence Clark
Well, it’s time for me to write my last column as the traveling machine shop trainer. I’ve decided that after three fun years traveling about the country meeting people and talking shop to try something just a bit different. I started working for Gary Reed at Lock-N-Stitch this past summer. I’m teaching casting repair to people in our industry both at the Lock-N-Stitch school in Turlock, CA, and on the road.
I’d like to take this opportunity to thank my sponsors, Clevite, AERA, K-Line, U.S. Tool and Mfg., and Lock-N-Stitch for allowing me to turn a dream into reality. Also, of course, I’d like to thank Engine Builder magazine for giving me this space to talk about the business as I saw it. I know there were occasional differences in my opinions from some of yours, but Bill McKnight, my friend at Dana/Clevite, tells me diversity is good for us all. It would be a pretty boring world if we all thought, talked and acted alike!
I’d like to introduce you to a couple of other rebuilders who have a story to share. John Konecny, McKnight’s partner at the Dana/Clevite training center, and Bob Fall, former Dana instructor and owner of Fall Automotive Machine in Toledo, OH. They’ve got an interesting story to share with you regarding magnetism in crankshafts in this month’s column.
Hello Engine Builder readers, John here. Bob and I have known each other for years, and we still talk every few days and have Sunday breakfast together almost every week. Both of us have spent almost our entire adult lives working on engines. We like to discuss issues, problems and new technology every chance we get.
This story starts like many do – by accident. I was checking a block on a recently assembled short block with my Gauss gauge, looking for any residual magnetism. I’d become more conscious of residual magnetism after reading one of Clarence’s articles last year in Engine Builder magazine, so I was checking lots of stuff. I wasn’t really expecting to find anything, just checking. I accidentally moved the gauge near the crankshaft and wow! There was major magnetism present. We had "maged" the crank in class and demaged, too. What was going on here? I started thinking what we could have done during the rebuilding process to cause the problem. The only thing I could think of was balancing. We’d balanced the crank, could that be the problem? I called Bob and asked if he demaged cranks after balancing. "No, why bother?" he replied. "I do just like you do: mag then demag then check carefully with the Gauss meter." My question sparked his interest, however, and we both were interested now. What was going on?
One of the advantages of working at the Dana Center of Technology is we have a certified metallurgical lab. I talked to Dana Combs, our resident metallurgist. Dana introduced me to a research paper from Wei-Chang Zhong, a scientist from the Gas Turbine Research institute in the People’s Republic of China.
The paper had to do with spontaneous magnetism being introduced into parts in the machining process. It was caused by rotating cutting tools. Not stopping there, Dana also showed me research indicating that magnetism in parts could also be caused by magnetic chucks, large AC motors being turned on and off near the part, and arc welders. I talked to Bob and we agreed to do some research.
We both have balancers so we decided to duplicate each experiment at both shops. First we tried the electric motors. After mounting our demaged crank in the balancer, over the course of a couple of days, we turned the motor on and off several dozen times. Nothing!
Next, we tried attaching and detaching the magnet used to pick up rpm on our balancers. It’s quite strong and we thought it might be the problem. Again, nothing. Then we both welded on the cranks while they were mounted in the balancer. Nothing!
The last thing we tried was drilling holes in the counterweights, just like we do during a normal balance job. Pay dirt! We had magnetism. The bigger and deeper the hole, the stronger the magnetism. Looks like Wei-Chang Zhong is correct. Bob says he even remembers balance jobs in the past where the holes had been deep and the chips wouldn’t fall out when he rolled the crankshaft over in the balancer.
We knew we were onto something now. We verified our results with several experiments, checked back with Dana Combs and implemented a new policy for both of our shops. Any crankshaft that’s been balanced gets demaged after all the machining is completed. We still check shafts to be sure, but since we’ve changed our procedure, we no longer find magnetism!
In fact, since our discovery of residual magnetism in the cranks, we’ve both been much more conscious of magnetism in all the parts we work on. We demag heads and blocks today, and routinely check all of our ferrous parts with the Gauss meter.
A very helpful source of information on this subject is a company called Electro-Matic of Chicago, (www.em-chicago.com). They sell Gauss meters and demaging equipment. In our shops, we’re real effective at demaging blocks and heads just using the electro-magnet we use to check for cracks. We leave the magnet energized and slowly pull it away from the area being checked for cracks. Re-checking with the Gauss meter has shown this to be pretty effective on heads, blocks and con rods but not effective on crankshafts.
We use our mag machine to demag the crankshafts. Our current machine has a demag circuit; on our previous machine you passed the energized coil completely along the crankshaft from one end past the other. I believe the difference in one machine is an AC machine, the other a DC. And follow your manufacturer’s instructions for your machine!
Learning Curve will continue to address the concerns of shop training in Engine Builder magazine. Please send us your suggestions. learningcurve@engine-builder.com