My Hobby
By Ken Hurst

Making a 180 Degree Crankshaft By Ken Hurst Selection of the right materials Mild steel--this material will work on engines that have no loads and that are just spinning a flywheel. 4130-4340--this material is heat treatable and will make a tough crankshaft and will take touque load of the engine. Planning your machining operation The setup is the key to having a straight & true running crankshaft Mill your material to the desired lenght ,withe & thichness , I machine it to the sizes on the plan Establish the center of the journals--Center drilling , use a center that will support your work, if drilling more than 1 center insure that all centers are drilled at the same depth. Machine slots for rod journals--Establish the center lines for the rods & center distance, this is to put the piston in the center of the bore. I machine the slot to size. Example plan has .375 thats were I put it.Leave enought material to machine journal later. Now were ready for the lathe operation of turning the journals Make special turning tool for the machining of the journals, high speed is the material I use. I turn all the rod journal before machining the main bearings---this is were fixtures are critical to hold min. run out & make the crankshaft rigid. Machine to .015 oversize for grinding. Machine journal closest to the lathe chuck. End for end to do the other journal. Now I finish the journals by grinding to size. I use a tool post grinder. Now all the rod journals are machined true & sized we can start machining the main bearing journals. Mill all excess material on ends and remove the rod journal centers & machine excess material of the center main bearing. Same as the rods I maching it to size. Install fixtures on the rod journal to support the so the crankshaft does not twist & so you can apply center pressure without distortion. Machine ends & center bearing .015 oversize & final grind after all material is removed. All that is left is threading the ends , removing the excess material between the rod journals & Drilling oil passages . After all machining is done check for straightness, correct as nessary to get run out within .001 TIR If heat treating is done leave all journal oversize, drill oil passages & after heat treat check for straightness & final grind.