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gearbox mainshaft

  • 07 Oct 2019 8:35 AM
    Message # 7920906

    In reassembly of my gearbox I've run into a "situation" with the mainshaft.  I've got new bearings with correct dimensions (Walker supplied) but I'm using the same mainshaft, sprocket drive gear, seal retainer, chain sprocket, and nut for the chain sprocket.  If I install the smallest thrust washer (.060) on the shaft on the sprocket driver end then the shaft doesn't protrude far enough out beyond the chain sprocket and nut to expose the shoulder on the shaft for the cupped spring washer to ride on.


    If I reduce the dimension of the spacer collar behind the chain sprocket then that will make it work, OR if don't put in a thrust washer next to the sprocket driver gear then that will give me the clearance I need.


    The bearing is fully seated, the spacer collar is .57 and I believe that's correct.


    I don't know what changed, and I did not pay attention when I took it apart last year!  Any ideas?  Thanks!


  • 07 Oct 2019 12:00 PM
    Reply # 7921281 on 7920906

    You know, when I look closely at the transmission diagram (attached here) I do not see a thrust washer on the sprocket driver gear side at all.  So maybe that's all there is to it, thrust washers on the clutch side only.

  • 08 Oct 2019 6:29 AM
    Reply # 7922514 on 7920906

    The diagram is showing the older gearbox with the small clutch and those don't have a thrust washer at the sprocket side, the newer gearboxes with the large clutch and clutch side bearing mounted from the inside, has different thickness thrust washers at both sides, the thicker one at the clutch end.

    There's something strange going on with your gearbox as the drive gear threads doesn't reach all the way to the nut end. The threads should reach the full thickness of the nut. Perhaps the drive gear doesn't seat against the bearing completely or have you put a shim between the bearing and the drive gear? Is the distance ring made too tall? 

  • 08 Oct 2019 9:37 AM
    Reply # 7922726 on 7920906

    Thanks Charlie.  I think I'm going to proceed by reducing the length of the spacer collar.  When on the bench, the chain sprocket will seat in the splines well enough so that the nut will fully thread onto the driver gear.  But when I view the back of the chain sprocket along with the spacer collar and bearing I can see the there is not enough room for the bearing and collar together when the nut is fully threaded on. 

    This may be a sprocket driver gear acquired later and made slightly wrong?

  • 08 Oct 2019 4:00 PM
    Reply # 7923426 on 7920906

    Wait a minute with making the collar shorter, check the gear dimensions first, as you have an additional problem with fitting the thrust washers.

    Last modified: 08 Oct 2019 4:02 PM | Carl-Erik Renquist
  • 08 Oct 2019 6:54 PM
    Reply # 7923673 on 7920906

    That is a very valuable graphic, thanks Charlie!  Of course with a gearbox that is 90 years old it is most likely a few things in there have been replaced!  So I will measure, and measure again.  One thing I found out today is that my sprocket is .276” wide at the splines, while another fellow measured his at .233”...I can use that .043.  Not certain if this sprocket is correct, it is dished on both sides while sprockets sold by Greer are flat on one side...so maybe a sprocket from Greer has less depth on the splines?

  • 09 Oct 2019 5:33 AM
    Reply # 7924201 on 7920906

    Most important is that the nut has full thread cover. Don't overtighten as the threads are fine thread, thus clamps hard with less tightening force compared with coarse thread.

    Be absolute certain that the sprocket is correctly hardened, a soft sprocket might destroy the drive gear splines irreparably as the sprocket will start to distort at the splines and loosen up the nut.

    Even a hardened sprocket can loosen up the nut and then the sprocket wanders out on the thread. When that happens the sprocket will spin and destroy the edges of the splines and also destroy the fine thread on the gear. 

    Absolute make a security screw that secures the nut from falling off the threads. It might be difficult, almost impossible to cut threads in a hardened sprocket but one remedy is to drill through and spot weld at the backside, a threaded pin where a safety lip can be bolted to. 

    The way I did it with a folding washer was not sufficient even if the screwhead prevented the nut from unravel totally, I was lucky there. The sprocket wasn't hardened.

    The ruined gear is from another sample where a hardened sprocket destroyed the gear irreparably. There is tremendous forces at the sprocket splines with the jolts, tug and vibrations from the chain. In addition to the security lip, use hard locktite as extra safety.

    Last modified: 09 Oct 2019 6:00 AM | Carl-Erik Renquist
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