500/550 Pinned Rocker Shafts + a rebore question

[Seabeowner]

I notice on my 550k that it has pinned rocker shafts. Apparently introduced after premature wear of the cylinder head cover. Strange that it only became apparent after quite a few years on manufacture of the 500/550s so may have arisen for other issues at that time.
As I have a spare cover my question is, is it really necessary and has anyone tried modifying an old cover and shafts to stop the them moving?

And while I'm here and it's ***** outside. Just measured up my spare cb500 block by positioning a ring at various points and checking gap. To sum up the bores are fine over the whole length except the final top 6-8mm of the stroke and then goes out to what I calculate as top just over the top limit 56.1. Is that normal, but presume that it's rebore time?
Thanks all

[matthewmosse]

My cb500 hasn't worn its rocker pins on her original motor and that did the bulk of 180,000 miles or so lugging a sidecar for the majority of that time so I personally wouldn't worry about retro fitting the modification.
Interesting what you say about the wear to the top 6-8mm of the bore, I geuss that is rebore time but I am no expert. Thanks for highlighting the small wear area, I'd better just check my engine there when I rebuild it, it wasn't out of tolereance but I think I measured mine lower down the bores, so there might be a spare set of new old stock rings surplus from my spares if mine is similarly worn and that does indeed mean rebore time. Over to the experts.

[Seabeowner]

Thanks for that Mathew. I'm also a bit suspicious of the mod as it did not appear before a long way through production and never remember it at the time. Perhaps it was a problem that affected a particular batch and the thought they should do something to restore confidence. The official Honda bulletin of course says that you have to replace the cover with a new one. I think the shafts were locked in place on the 350/400s but by a different method.
And on the bore question I could feel a line at the top where the top compression ring would reach at TDC. A loose ring above this gave a gap of about .012" and at about midway on the bore it was not much different. But when positioned a little way down from the top the gap increased to 0.027" Tried moving the ring around axially to do it a few times, but always same result. The feel at the top of the bore was the giveaway.