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

[K2-K6]

Yes, that's what you'd get if the rollers aren't all rotating in the same direction.

If the problem doesn't occur with a revised bearing it indicates the design of the first was wrong rather than the lubrication.

[AshimotoK0]

Here is the style of bearing Nigel

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[Trigger]

All the K0 shafts i have had problems with were all blue due to over heating. The other problem was a few had the oil guide plate missing ( PN 23106 323 000) and CMS list this plate on engine number 1018728 onwards. With out this plate the bearing was also burnt out and some had damage to the casing.

[AshimotoK0]

Here is the bearing on the countershaft  Nigel and a CB250/350K part

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[Rob62]

I agree k2k0.... I’m no bearing expert but that photo of the original bearing certainly puts the needles in pairs with close proximity to each other. Not sure what the benefits of that design would be? Maybe more to do with the strength/manufacture of the cage than the actual load that the bearing can carry... I would think that logically evenly spaced needles would offer the best support and avoid crowding... There must have been a reason behind the design.

[K2-K6]

Not sure I've got it the right way round about that paired semi crowded weird roller,  did they change that in the mod to different design or just change material?

That definitely looks like it could give a sprag clutch effect on the shaft.  If you think about it travelling around, the two rollers at their interaction with each other are going in the opposite direction while the bearing is rotating.  In a whole crowded race, each successive roller is subjected to the same and equally opposing forces.  It'll give friction which is why you'd head away from that for higher bearing rotation speed and toward a caged roller design to avoid that. 

But that paired roller design seems to be ok as long as tolerance is tight from inner to outer race, including roller dimension. But if you got any wear at all, then one of the pair would want to climb over the other and so set up a sprag clutch effect.  Ultimately it would try to grab the shaft but without enough room to shift it's geometry sufficiently it should rapidly build heat and/or damage the shaft surface.

Oil film doesn't servive in a sprag clutch as that is exactly what the mechanical ramping effect is supposed to do,  break down the lubricant until fraction bites the shaft and makes the components pinch each other to cause torque transfer.

[Bryanj]

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

[Trigger]

All of the shaft problems i have seen, have been on early K0's and nearly all have been around the 5.000 to 7.000 miles 
A member on this forum has a UK, 500K0 that has a locked engine at low mileage and i suspect that this engine lock is due to the shaft problem.

[deltarider]

All the K0 shafts i have had problems with were all blue due to over heating. The other problem was a few had the oil guide plate missing ( PN 23106 323 000) and CMS list this plate on engine number 1018728 onwards. With out this plate the bearing was also burnt out and some had damage to the casing.

I have the feeling this oil guide plate 23106-323-000 is of crucial importance. I always wondered why it was added like in mine and was not present in the early models.

[AshimotoK0]

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

Its at work Bryan ...I still need to scan it... I will check when I am next in. need to give you a call by the way...when is the best time please?

[Bryanj]

Gone part time now Ash, only do 45 hours a week working Monday to Thursday nights inclusive so one of those after 8pm mate

[K2-K6]

All of the shaft problems i have seen, have been on early K0's and nearly all have been around the 5.000 to 7.000 miles 
A member on this forum has a UK, 500K0 that has a locked engine at low mileage and i suspect that this engine lock is due to the shaft problem.

Could you try with it in gear to push it backwards and see if it moved? If it has "spragged" it may release it.

Or pull the clutch pack out of it to disconnect the motor from the main shaft completely,  then try to turn it over to see if it's unlocked. 

It would tell you if it's hanging up on that bearing or not.

[AshimotoK0]

I still can't get my head around why they chose that type of needle roller bearing for the main-shaft. A lot of that gearbox was cribbed from the CB350K design including the needle roller bearing on the counter-shaft but the 350K didn't use the paired roller type. The 400/4 uses two identical bearings, still 20mm but with 'open' ends but does not use paired rollers in the cage. The 350/4 uses similar bearings to the 400/4 but with 333 centre number (400/4 is 377). Interestingly, I just stripped down two Black Bomber CB450 gearboxes and they use two brass coloured  plain bearings in those locations.

[K2-K6]

Is this what was happening here?   http://www.sohc.co.uk/index.php/topic,15545.90.html

Sounds like it could be the same thing, 4th post from last on this page.

[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.