GEARBOX MAINSHAFT SPACING

Discussion in 'Norton Commando Classic Motorcycles' started by edward, Nov 10, 2017.

  1. edward

    edward

    Joined:
    Jan 3, 2013
    A loose mainshaft bearing has allowed the sprocket, sleeve gear and bearing to move slightly inwards resulting in the chain gouging a groove into the back of the gearbox. I dry assembled the box with the inner case and mainshaft with gears and found that when the bearing is loose the sleeve gear can slide in 1.5 mm. before it come up against the shoulder on the spline. Is this normal or is there anyway of reducing this potential movement with shims? Obviously its not an issue if the bearing remains tight in the housing, but if it becomes loose again during service I'll have the same problem.
     
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  2. RoadScholar

    RoadScholar VIP MEMBER

    Joined:
    Dec 28, 2008
    I looked at the parts fiche to confirm what I thought I knew; that being there is no shim for the main shaft, and that the only parts preventing the sleeve gear/bearing from moving right is the countershaft sprocket, and, of course when the sleeve gear/bearing moves right it ends up being the chain that stops further rightward movement by dining on the transmission case, as you have discovered.

    You may be able to knurl the bearing or the bore that it fits in. Loctite makes a product called bearing mount, green, I believe, that may be a solution, although my experience with Loctite products leads me to believe that heat loosens the bond, others may have a better view of this, can't say.

    I also wonder if the outer race of the bearing could be notched/channeled along with a drilling in the case to comprise a hole that could be tapped and then use a grub screw to stake the bearing, possibly two screws at 180 degrees to insure that the bearing remains centered?
     
  3. Torontonian

    Torontonian

    Joined:
    Dec 28, 2009
    I would not trust Locktite to fix bearing drift. Stake, pin or screw it firmly into place.
     
  4. fiatfan

    fiatfan VIP MEMBER

    Joined:
    Aug 9, 2015
    I was just the other day given the advise to scrap my gb housing because of this exact problem. It seems both the main shaft and lay shaft bearings have spun in the housing. A po have even tried to punch markings next to the bearings to make them sit tight. And lots of bearing mount as well. Doesn't seem to have worked out. I've also thought about locking the bearings down with a screw somehow, any more ideas on this someone? I also thought that maybe I can find bearings with a slightly smaller outer diameter, and press fit a steel ring on it which have the right outer diameter to fit correctly in the housing. Probably small chance to find such bearings, but I'm gonna at least try.
     
  5. kommando

    kommando

    Joined:
    May 7, 2005
    Have a set of new bearing copper plated on the OD to get the interference fit back. The copper is soft enough to be removed if the deposit is too thick and hard enough to work in the housing. Loctite does not work on a steel bearing in an alloy housing.
     
  6. fiatfan

    fiatfan VIP MEMBER

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    Aug 9, 2015
    Interesting, where did you get those? And can you get any bearing size?
     
  7. kommando

    kommando

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    May 7, 2005
    You buy std bearings and then take them to you nearest plater, they will apply varnish or wax to the places not to be plated, common fix in factory maintenance Dept's.
     
  8. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    I doubt you’ll find suitable bearings with a satisfactorily smaller OD to allow sleeving. You may solve one problem, only to cause another, ie bearing failure.

    If you are a competent DIY machinist, then pegging / screwing could work well. But if you have to pay a machine shop to do the work, just remember that a new shell is around £330. You don’t have to accumulate many machining hours before the cost of a new shell starts to look attractive.

    Kommmandos copper plating idea would seem a low cost fix option that doesn’t require competent DIY machining abilities. My only question about this is: the shell is already weak in this area and prone to cracking between the bearings. When making the bearings oversize, is there a risk of putting in bearings that are too tight and increasing the risk of cracking the shell?

    However, if your bearings have been spinning as you describe, are you sure the housing is not cracked already between the bearing housings? Whilst many owners state that a cracked housing can be used without trouble, IMHO it would seem false economy to invest very much time and / or money on an already cracked case.
     
    Last edited: Nov 14, 2017
  9. fiatfan

    fiatfan VIP MEMBER

    Joined:
    Aug 9, 2015
    As far as I can see there's no crack/s in the housing, and if there was I wouldn't use it. I'm not a machinist, but I have a friend who is, and I sort of like the idea of locking screw/s. Just hope it doesn't weaken the already thin material... at times I just tell my self buy a new box but I can't seem to make up my mind. Since I have severe pitting on every gear as well, the cost is running away, fast.
     
  10. fiatfan

    fiatfan VIP MEMBER

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    Aug 9, 2015
    Ok, is there any way to determine how thick the copper layer will be? Seems pretty important. But as I said, interresting.
     
  11. seattle##gs

    seattle##gs

    Joined:
    Oct 28, 2014
    I recently had a crank bearing hard chromed for the same reason. It was $180 here in Seattle.
     
  12. kommando

    kommando

    Joined:
    May 7, 2005
    You want 2 thou interference on the large bearing but 3 would not be amiss, 1 to 1.5 on the smaller one. The copper plate is the cheapest and softest so you can over plate and the size using emery paper.
     
  13. Bob Matthews

    Bob Matthews

    Joined:
    Dec 19, 2016
    My worry would be that any bearing that has spun in its housing, would not wear out the housing in a concentric manner - it would nearly always wear at one side depending on which way the thrust is and therefore wear an oval hole.
    So to fit an oversize bearing (or plated one) could be a very hit and miss situation.
     
  14. ashman

    ashman

    Joined:
    Jul 10, 2010
    I have used Loctite shaft fit on lose bearing which is green in colour and it worked a treat the bearing outer stayed in place, but if the grooves in the case from the outer bearing is to much then maybe some JB weld on the GB case where the bearing sits with the bearing put in while setting.
    There must have been a problem with the old bearing to make the outer bearing spin in the case in the first place as the inner bearing should be taking the load of the shaft and gears.

    Ashley
     
  15. YukoNorton

    YukoNorton

    Joined:
    Sep 3, 2017
    I think as kommando said for interference fit is good. In the machine shop and brit bike shops I was in, the general rule was .001" per inch for interference fits. Materials is a consideration. Further to Bob's concern, the housing could be machined with a 1 thou or 2 though cut (just enough to clean it up) to oversize the bore, then the bearing race plated with copper (or nickel) and machined to fit the new oversized housing with the original interference fit.
     

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