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  1. #1
    Join Date
    Jul 2016
    Location
    Melbourne
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    35
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    1,522

    Default Early motorcycle fork bearings

    I have been chipping away at a motorcycle project for a long time, its a 1924 Ace. The latest puzzle is the front fork bearing races. The setup is as the photos show, an inner race is just the cone feature on the knurled nut (photo 1), those have been remade quite some time ago. Its now my task to make the two spigoted outer races, these have been badly brinelled/dinted from hard impacts over the years.

    They are reasonably hard but nowhere near as hard as a modern bearing race, I would say somewhere like 40 - 45 rockwell. they dont show signs of being ground just turned but do seem to have been nickel plated. the balls were just packed in with grease no cage.

    My questions are:

    Would the inside of the race really have been plated, I dont think nickel would really hold up even in a low force, low speed, high load situation like this, unless its harder and more robust than i think.

    How should i go about grinding that ball form into the cup, I do have a rudimetary tool post grinder, just a ball tip on that? I would think it might be quite a load grinding all that surface area.

    Should I go for a higher hardness for better impact resistance or do i need the toughness?

    Normally i would just shove a tapered roller in there but in this case it needs to be kept original. Note there are two identical setups, top and bottom of the fork housing

    Regards - Ralph20171231_125007.jpg20171231_125023.jpg20171231_124957.jpg20171231_124953.jpg

  2. #2
    Join Date
    May 2013
    Location
    Adelaide Hills
    Age
    59
    Posts
    7

    Default

    Hi Ralph, that's a classic indeed ! Not sure whether you have tried searching for parts or you are keen on making them.....couldn't help but search for info out of pure interest......quick search and this may or may not be relevant. Ace Parts . Tis some years old now but hopefully may be of some help to you.

    Good luck, a beautiful classic you have.....!!

  3. #3
    Join Date
    Jul 2016
    Location
    Melbourne
    Age
    35
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    Default

    Sorry if it wasn't clear, I'm always on the lookout for parts but in this case im looking to make them. Thanks for the link though.

  4. #4
    Join Date
    Aug 2010
    Location
    Toorloo Arm, VIC
    Age
    39
    Posts
    1,270

    Default

    I reckon in this particular case, there's a very real danger of overcomplicating it (I know I would!). The reality here (IMO, of course) is that as the groove for the balls to run in doesn't actually need to do much other than stop the balls walking in and out with respect to the centre, the exact profile of the groove shouldn't really matter too much to my mind. In fact, I wonder whether a straightforward V-groove might actually be better in terms of longevity, by spreading the load over two flanks as opposed to the one flat (?) surface it currently uses. The preload appears to be externally set, so that makes life easier. I doubt there's really a need to grind the race, if you can get a good surface finish off the lathe - any machining marks will run in the same direction as the balls are traveling and won't cause any notchiness in the action, a bit of sandpaper as a final step would probably do just fine? Of course there's no harm in grinding if you wish, but I wouldn't get to hung up on it needing to be part of the process.

    In theory, if the preload is correctly set, I'd think seat wear should only occur very slowly over time, the majority of any impacts being absorbed by the forks. If the preload gets a bit loose however, and there is some endfloat of the steering head in the frame, that could begin to chew things out very quickly, even on hardened components - as you now have a hammering action going on between the race and the balls, as opposed to an almost rigid assembly. Even modern bikes chew out their tapered roller steering head bearings under this condition... Also keep in mind, with most motorbikes, once they're up to speed, the steering really doesn't get turned more than a couple of degrees either way, meaning the balls spend most of their life in the same spot. I think it's possible the wear you're seeing is not so much from hard impacts (at least initially), but simply that the balls have constantly worked those spots over many years. The resultant decrease in preload would then certainly allow impacts to cause accelerated wear...

    I'd certainly think it possible that the original races were indeed plated in order to prevent rust, as if the preload is correct I feel they should be under very little load really, but whether that was nickel plating, or perhaps hard chrome, that's another matter...

    As for hardening the seat - I'm not sure its needed - to my mind if the preload is set correctly, a reasonable hardness steel 'as is' should be more than fine.... However, the big determining factor in all of this, is how often will the bike actually be ridden? If it's every second Sunday for an hour or two, replicating the original setup in the simplest way possible should give a service life far in excess of your requirements, especially if the preload is kept in spec and lubrication is maintained. If you're going to use it daily, then you might look at hardened seats, and the highest quality balls you can find. All of which, again, will do no good if the preload is wrong...

  5. #5
    Join Date
    Jul 2016
    Location
    Melbourne
    Age
    35
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    Default

    Thanks Jekyll, you make great points, it really will see very little use so i will go with a carbon copy of the original assembly, unground.

  6. #6
    Join Date
    Jul 2012
    Location
    Malvern East
    Posts
    84

    Default

    Hi yah an interesting project you have going there old style cup and cone bearings by there nature are not ground and in many early vintage sets I've played with 1911 and !927 era stuff the head set cups and cones where say an en24 and case hardened 5 thou max interesting is that most of the items i have played with are / where only ever turned finish i.e. form tool not that the radius was also say 20 thou bigger than the ball used i.e. not the same radius when i had my bits nickelled they just wax stop off the race area and into nickel plating bath it goes no need to worry about embrittlement as its just a flash and the deposition currents are not as high as chrome

    Even modern postie bikes are still cup and cone to this day just a 5 thou case on them maybe even less these days with nitriding etc just turned never ground and its no use trying to grind them you go through the case too easily

    Good luck with it mate

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