Just get 4203 bearings in 2RS (fully sealed) if you can, its that simple.
The stock 4203 was an open bearing with felts, 2RS if you can find them will be fit and forget given the average age of the members here.
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I personally do not use Made in Timbuktu bearings in my bikes and some years back the only 4203 bearing I saw available were the sets from Don Pander.
The complete unbranded set I bought (both wheels) is "rusting" away on a shelf somewhere.
Luckily I found the fantastic Old Britts website (Hello Fred and Ella) and there was a quality fix.
As far as the front disc brake hub, the 5203 bearing (same OD and ID as the 4203 but around 1.5 mm wider >iirc) could be used and even for me Downunder was available off the shelf from the closest bearing/seal retailer (Industrial in my case)
I doubt anyone would be confused with, remove the extra width (1.5mm iirc) of the bearing from the spacer tube and fit the 5203 bearing so the outer measurement across the left and right bearing is retained as it was with the narrower 4203 bearing.
Its that easy.
Infact if there was a quality 4203 2RS bearing available now (I have not checked) I could simply buy a new spacer tube from Andover Norton (US$5.57) to replace the one I machined and fit that 4203 after removing the wider 5203 I have in there. (Not that I would)
If you have the means (machine tools at home) , is it worth fitting a 5203, probably not if a decent (2RS) 4203 was available unless you consider the 5203 an improvement.
My 850 also has taper roller steering head bearings (with the spacer tube shimmed to set the clearance so the lower stem nut can be torqued to spec)
Is that better than the stock ball bearings, I think so and because I could do so easily.
In hindsight I could have used a taper lower bearing and a ball upper bearing.
I simply try to make the most of what is there while retaining the outward appearance of the motorcycle and nothing is to much time or trouble and that applies to all my 'old motorcycles where possible.
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One for Al.
Could they be the only set in the world.
1973 Moto Guzzi drum brake forks (steel sliders with welded on axle block) modified and jig re-welded to take Showa 20mm cartridges.
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