Apparently, "back in the day", output shaft bearing failures were known to occur, also chain breakages. I do wonder how much of it was down to the use of inferior / badly worn and/or adjusted chains (if chain tension is too tight for any reason, it will give that output bearing a hard time, particularly as chain tension changes as the rear suspension goes up and down). My#5298 when stripped at 32,000 miles ran well enough, but did have some pitting of one of the output shaft bearing races maybe due to it having stood for many years (roller /ball bearings do not hold oil when stood, and so can dry out and suffer light corrosion due to condensation or damp, which can then cause bearing track pitting). Both bearings were changed of course, but only with the original single row ones (genuine NOS Honda parts)
#5298 now has 122,000 miles on it, so 90,000 miles (UK touring two up,track days, hard use on the Isle of Man TT circuit, etc) on those replacement "skinny" bearings. I do not believe it is necessary to upgrade if good quality modern chains are used (I use DID or RK heavy duty type non "O" ring type with the press fit side plate/split link) and correctly maintained, which in my case includes fitting of a new chain every time the rear tyre is changed.
It is possible to fit the later K3 type double roller output bearing into earlier engines, but only if the later output shaft is also fitted. For those that are worried about bearing failure, I suppose that would be a way to upgrade, although the double row bearing will still not be fully supported by the crankcases due to the casting thickness in that region being less in sandcast cases than in the later K3 cases which the double row bearing is intended to fit.
Just my experiences / view - we should each do whatever we feel comfortable with.
Cheers - Chris R.
