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how are rod journals ground on a crankshaft?

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  • how are rod journals ground on a crankshaft?

    i was just wondering about it. i have the engine in an old Farmall F-14 just about down to the bare block and probably need to have the crank cleaned up. main bearings are easy to figure out, but how are the rod journals machined? and are they cut or ground?

    i'm not planning on attempting this myself, i was just wondering. anyone have a photo of the jigs required?

    andy b.
    The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

  • #2
    The rods are usually ground. The crank is held in the grinder by both ends, it is adjusted so the journal to be ground runs true and the rest of the crank runs out. Crank slowly rotates wile being ground.

    There is also an old grinding fixture that can be connected down through the cyl. bore to the rod journal to do an inframe crank grind. The crank slowly turns as the grinder follows the throw. I had a chance to purchase 2 of these at a auction, very old technology but worked in its day. Sorry no picks.Hope this helps.


    • #3
      I saw a homemade rig about six months ago.

      The collets were made like a 4 jaw chuck, adjusted out of synch with the center so the throw rotated "centered" and the rest of the crankshaft went around in a large path. There was a bolt on collet for each engine type. You rotated the collet for each throw.

      INstead of the expensive grinding rocks most people use, he had belts of varying roughness and a stainless steel strap to ride over the belt to hold it flat. A spring held tension on it and a finger rode on it giving indication of cut depth. His cranks looked like mirrors. You have several measurements to maintain on a crank, depth for oversized thicker bearings and side to side. Not sure how he maintained the side to side clearances. He had numerous straps.. It looked like a cobbled up knife makers rig.

      The "real" builders tell me a polish job is wasted money, but I sure like em slick.

      I got three motors tore down right now. I bored a pulley so slick today I was wishing I had the tooling to bore two of the three motors here.



      • #4
        Crankshaft grinder:

        The centers are adjustable to offset the crank to line up the throws with the axis of the grinder.


        • #5

          Modern production methods use (ceramics for roughing and CBN for finishing) CBN inserts to turn prehardened forgings from the rough state to an "as ground finish" in one machining operation - this is refered to as "Hard Turning". This eliminates one machine set up as only the rough blank is set into the special lathe and turned. It produces a finish better than most commercial grinding operations can provide at far lower costs and higher speeds. Most modern engine cranks are done this way and many gearbox and suspension components as well.


          • #6
            Crankshaft production process of Chrysler 3.5L V-6
            1) Rough forgings (yes forgings) are spun in a prebalancer to center the crank mass prior to the centering process. Crank is centered and post and flange ends are roughed
            2) Mains and counterweight ODs are turn broached in one revolution of the cutter while crank is spun at around 450RPM
            3)Crank throws are milled in Heller CNC pin chasing mills
            4) Oil holes are drilled through crank from mains to pins
            5)Flange and Post ends are finish turned and all hole work on ends done (tapped holes for swash plate, index locator for pin grinders, drive flat for oil pump drive gear, keyways for timing belt sprocket ets)
            6) All Post, Flange and Main Bearings ground on series of Landis Grinders
            7) Pins Ground on Landis Pin Chasing Grinders. On these grinders the crank runs on the Main's centerline and the Wheel Head continually moves in and out to keep the wheel tangital to the bearing OD
            9) Crankshaft run through finish balance operation consisting of first balce check, weight removal, second balance check, finish wight removal and final balance check
            10) Lapping operation on pins, mains and thrust surfaces
            11) Washing operation
            12) Either goes into float or right to production assembly operation. Potentially the crank can go from step on to being put into the engine with only being handled by one person. The one who put it on the line in the first place. In various spots of the production process there are a number of automated holding areas for storing parts if sections are down for tool changes or breakdowns.

            How this all helps with a Farm-All I have no idea
            Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.


            • #7
              F-14? Those engines I like,what is there 13 or 14 parts total

              That should have babbited rods and hand holes in the side of the block(how convienient)for each of the rod journals.

              They used to touch those up with a facing tool that resembled a pipe cutter.Rollers on oneside,stone on the other.They would power the operation through the takeoff shaft with a flat pulley.
              I just need one more tool,just one!


              • #8
                David said, "It looked like a cobbled up knife makers rig."

                Hey! Quit makin' fun of my Model T tools.


                • #9
                  thanks for all the replies!!!! and also thanks to Carl for the photo of a fancy modern machine to do it. i figured the crank was held in a jig so it turned around the rod journal, but it sounds like there are several ways to do it (and not all center on the rod journal).

                  as for wierdscience's comment on parts, i was telling a non-mechanically-inclined co-worker about it, and he asked how i could figure out how to get it back together. i told him i could pile all the pieces on the floor in front of my desk and there would maybe be 50 pieces and they can only fit together one way. it isn't like a modern car engine.

                  no Babbitts either. this is a MODERN engine from the 1930s, not one of those old 1920s engines.

                  andy b.
                  The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining


                  • #10

                    Just curious, can you still get parts for that engine?