Warning to 500K0 owners--dodgy mainshaft needle roller bearing

[AshimotoK0]

Ash, what is the part number in the Japanese parts book?

I just checked your Japanese parts book Bryan and it was published in 3/1971 so must have been the very first parts book for the CB500K0 and the bearing number for the main-shaft is exactly the same i.e. 23931-323-004.

I will talk to you next week when I call you about scanning it.

[AshimotoK0]

I just secured a NOS replacement from DS and he has a few left if anyone needs one. Looking at the USA SOHC  site that bearing was a hard to find item a while back.

https://www.davidsilverspares.co.uk/parts/by-part-number/partnumber_23931323004/

 Unfortunately nobody seems to have the countershaft needle roller bearing at a reasonable price. 91023-286-016

[K2-K6]

Like you Ash and Rob62,  I don't understand why they've specified a strange bearing there.

Ordinarily you'd guess the reasons for change would be chasing load capacity and/or durability.  But why a paired roller? I'm at a loss to see a rational path to that design. Must be something we're missing,  I don't recall seeing another of that type though across many different applications. They have plenty of things to play with in shifting roller number and size,  but why pair them?

On a slightly different, but related note, just going through some old bike magazines and CMM March 2011 has a picture of a proud 400 Four owner, is that you Ash?

Nigel.

[AshimotoK0]

Like you Ash and Rob62,  I don't understand why they've specified a strange bearing there.

Ordinarily you'd guess the reasons for change would be chasing load capacity and/or durability.  But why a paired roller? I'm at a loss to see a rational path to that design. Must be something we're missing,  I don't recall seeing another of that type though across many different applications. They have plenty of things to play with in shifting roller number and size,  but why pair them?

On a slightly different, but related note, just going through some old bike magazines and CMM March 2011 has a picture of a proud 400 Four owner, is that you Ash?

Nigel.
 

Yes that was me but the bike is back to it's original Varnish Blue now.  That article was by Mark Williams and he got loads wrong... e.g.  I was restoring a rare sandcast 750 ...it was actually  UK K0 diecast but hey-ho.

[Trigger]

The bearing was not the problem, its the shaft !
You can get the needles on there own from any good bearing supplier 

[matthewmosse]

Interesting, looks like if I ever get around to doing my k0 up it's going to need checking before a run of any length. Another year or 2 and maybe the kids might want to see inside a bike engine or at least spend a few evenings over at friends houses. Are the newer cb500 bits retro fitable to the k0 gearboxes? I have plenty of those in bits to pillage for a replacement shaft or bearings. I'm not averse to 're using good bearings on a rebuild, having an old landrover there's a better chance original bearings will outlast brand new replacements. They have far better pattern parts availability on old landrovers but boy the quality and authenticity of some are appalling. It's a shame this cannot be checked by any other means than a full strip down of the bottom end.

[Bryanj]

Mayhew, later parts fit but some gears have to be fitted as running pairs