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Repairing a Sheared Key on a Pacemaker

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  • Repairing a Sheared Key on a Pacemaker

    I wish I could be more descriptive. There is a "jack shaft" which has two gears and idles between two bearings in the apron. One gear is within the apron and I'm going to refer to it as the bull gear. Then, on the outside of the apron, is the second gear. It is the pinion that engages the rack to move the carriage. That bull gear is driven either by the gear that is engaged by the auto-"lead" lever (to use Pacemaker descriptions) or by the gear on the handwheel shaft. That bull gear is held onto the shaft by a key and it is sheared in both of my Pacemakers!

    In my other thread I gave a description of removing the carriage and then removing the apron from the carriage. I'll pick up from there for repairing this key.

    On the front side of the apron there is a round cap that needs to be removed. A shaft with a nut and lock ring will be exposed. After bending the tab back, the nut must be removed. Then, the apron "cover" can be removed. Here is a picture of the cover being seperated from the apron. There are four, iirc, SHCS that need to be removed and then there are four dowels holding it in place. Then, the set screw (clearly visible in this photo) needs to be loosened. As long as the handwheel shaft is removed, there is nothing else preventing this cover from being removed. As it is removed, the bull gear, pinion, and "jack shaft" will come with it.

    Here is the cover once removed:

    Now, theoretically, you could remove that round cover, nut and lock ring on the front side and just tap the shaft out and then pull the gear out from between the apron and apron cover. In this case, though, after the key sheared it jammed up real good. In fact, I would never had noticed, except that I knew I had a sheared key somewhere in the other pacemaker so I decided, while this one was apart, to do some exploring. I thought I'd take it apart on this one as a "practice run" so I'd know what to do on the other.

    It turns out that the bull gear was stuck on there so hard that it took a 50 ton press to press the shaft free from the bull gear. I sweated bullets the whole time.

    First, though, I had to get the shaft free from the apron cover. I had to carefully tap the bearing out of the apron cover. I couldn't just hammer on the pinion gear, since all of that pounding would be transferred to the inner race of the bearing. I used a brass drift and carefully pounded on the outer race of the bearing. OOPS - not carefully enough! I bumped the shielding and crushed it in. There was already a section of the shielding that was damaged, so I wasn't the first.

    After freeing the shaft and then using the press to press the bearing off, I discovered the sheared key and damaged shaft. That would need to be repaired, but first I chose to address the bearing issue. (I was feeling like a real loser at this point since I didn't know there was anything wrong with the shaft. I was just satisfying curiosity when I damaged the bearing)

    I talked to ND, but they said they couldn't even match a bearing to the part number I gave them; it was too old! So I decided to see if I could repair it.

    Using a hammer and a scribe, I punched small holes and then bent the shield back up out of the race.

    The bearing is now useable. After opening up the shield and carefully reshaped it and did my best to close the holes back up. They are very small, not much bigger than a needle so it shouldn't matter too much. They weren't sealed bearings to start with, just shielded on this one side to keep swarf out.

    To remove the broken key, I had to weld a nail onto the the remaining bit of key. If the shaft is in half-way decent condition, I'd suggest wiping some oil on the shaft to protect it from spatter.

  • #2

    Here is a picture of the parts:

    Thats the other side of the bearing there.

    After removing the key, I built up the damaged part of the shaft and turned it true using a four jaw. I indicated off of the bearing journal. It was awsome using a nice indicator and a nice four jaw on a nice lathe! It took me about 5 minutes, if that, to get within .0005. Most of that was luck, but it was pretty sweet! :-)

    After that, and installing a new key, it was time to put everything together. Put it together just like it came out!
    Last edited by Fasttrack; 07-03-2008, 01:09 AM.


    • #3

      Well... I reckon that does it for this part. Next up is repairing the oil plunger and cleaning the oil passages. That is a little more complicated in the disassembly but not too bad. Just have to deal with the half-nuts.

      Better take a break though, I'm tired and my laptop is running out of juice!
      Last edited by Fasttrack; 07-03-2008, 01:11 AM.


      • #4
        You're doing a great job FT. Reminds me of all the stuff I found wrong in my Logan. Sheared pins, damaged shafts, worn bushings, etc. But my Logan sure didn't need a forklift to lift the apron! LOL! Them Pacemakers must be massive.



        • #5
          The apron looks like its in pretty good shape. Those half nuts look like they mean business.You got yourself one hell of a bargain.
          I'm envious.


          • #6
            Looking good,in case you ever run up on one again obsolete New Departure replacements can be found here-


            Your local-


            branch can get them for you.
            I just need one more tool,just one!


            • #7
              Geez, you think those apron gears are stout enough. Look pretty flimsy to me, might wear out in a few hundred years of 24hr shifts.


              • #8
                Originally posted by wierdscience
                Looking good,in case you ever run up on one again obsolete New Departure replacements can be found here
                New Departure went out of business years (decades?) ago, but they're almost all standard bearings sizes. Get a bearing cross reference guide and buy some modern replacements (for a whole lot less than NOS New Departure bearings).
                "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


                • #9
                  That must be a double row ball bearing, It sounds like your keeping one lathe up and running to fix the other and swapping back and forth? if so how cool is that, Dont beat yourself up about the "baff's" To a certain extent its all part of the exploration game, and you do need to "go there",,, If you dont you will always be wondering if its right or not, not only that - you may be letting a serious problem go unchecked and it could turn into a real serious problem or even a safety issue, Tear into her -"git er done"

                  The bearing shield sounds like its as good as new, Like you stated its only a shield, Iv had to straighten many a real seal on bearings after re-greasing them, Iv also drilled little holes in the side (with grease to catch all the shavings) and then pumped grease into them - then brake cleaning the surface off and a dab of silicone over the hole, Biggest mistake I ever made on a bearing was doing just that and not keeping track of the amount of grease I put in, all you want on a total seal brg. is just a smidge --- I put too much in, It was a Mitsubishi eclipse timing belt tensioner (interference fit engine )
                  Lucky for me the belt change intervals are only 50,000 miles,
                  It was a steady customer, I tore into it a few years later to throw another belt at it and here's this bearing minus its shield, I bet it blew its shield 50,000 miles ago and ran half dry all that time, I got lucky, very lucky, The 2.0 mitsu doesnt just stuff its valves, it has a "unique" roller cam/rocker assembly - the rockers are actually free floating and sandwitched between the cam lobe the valve end and a hydraulic pivot, when the valves get stuffed they bend and no longer return all the way, then the rockers start dancing around and gain enough clearance to leave there designated stations, the results are devastating - they randomly get wedged between cam lobe and head and anywhere they can get caught (and theres 16 of them) broken cams - trashed head, Iv seen tons of them, they basically self destruct.

                  Just because I "skated" does not let me off the hook, this was one of my biggest "baffs" to date, I got very lucky, I try to save my customers money by not going too crazy on parts replacement if they dont really need it, Just because I "skated" does not mean this was a lesson soon forgotten, I'll never forget it! And I also never lost a seal since


                  • #10
                    Originally posted by lazlo
                    New Departure went out of business years (decades?) ago, but they're almost all standard bearings sizes. Get a bearing cross reference guide and buy some modern replacements (for a whole lot less than NOS New Departure bearings).
                    Actually, I think I've found more non-standard ND bearings than I care to remember. Lots of extended inner race bearings that appear to be unavailable now. Many time a spacer will solve that problem though.

                    Some of the common older Delta woodworking machines used ND bearings that are no longer readily available.


                    • #11
                      Yep - I measured the bearing and it was an odd-ball one. I can't remember now what the dimensions were, but it was a double row ball bearing. Maybe it was metric dimensions, who knows. Anyway, I couldn't find anything that was close but I didn't look particularly hard. I figured I try fixing it and see how that worked. If need be, I can replace the bearing in another few years when it fails. Its not too hard to get to. In fact, now that the key is fixed I can remove the bearing while the apron is still intact and installed on the carriage.

                      Thanks for those websites Weird - I'm sure they'll come in handy!

                      Thanks again AK - I wasn't sure my "bodged bearing" repair was an acceptable solution in the world of machinists! I am glad now that I tore it apart. I would've felt like I did a half-a** job otherwise.


                      • #12
                        Originally posted by lazlo
                        New Departure went out of business years (decades?) ago, but they're almost all standard bearings sizes. Get a bearing cross reference guide and buy some modern replacements (for a whole lot less than NOS New Departure bearings).
                        ND made many types of specials and OEM speced bearings that don't interchange with anybody.Some of those can still be replaced with standard ball bearings,but spacers will have to be made and shoulders bored back and re-machined.
                        I just need one more tool,just one!


                        • #13
                          Bearings aren't any problem if you have a good bearing house close buy. But one thing for sure when you are done you will know what you have and what makes it work. which is a whole lot more than most people. Keep up the good work. Fasttrack you are doing super good in my book.
                          Every Mans Work Is A Portrait of Him Self