Ken,
The cylinder bores still look ok, no scuff marks and can still see the cross hatch faintly.
Still on standard size.
Blaise
Not really sure what you are trying to achieve Blaise. Or how you propose to use the bike in future. Norman White told me a bore can last for 100,000 miles and I have no reason to doubt that. Your only concern might be marks from the broken rings and any possible ridge on the bore, there shouldn't really be much at 28,000.
A good fix might be new standard style pistons and a hone, or plus 0.020" rebore and new standard style or uprated pistons. New rings alone probably isn't a good idea since it is possible the top ring grooves have wear now.
You need to measure properly to see if just a hone is viable, it should be.
JSM long rods and pistons are certainly a fix, but compared to standard height pistons an expensive one. And again, hone at standard JSM clearance or rebore will depend on how they measure up.
There would be no need to assume there is a problem with the standard rods and that they won't continue to give good service, but crack testing whilst they are out after 44 years isn't a bad idea.
I use JSM rods and pistons in a race motor, there are a lot out there who do. It can destress an otherwise stressed motor and I would recommend them to anyone building a high performance engine, particulary one to be used rigidly mounted, like mine. Don't forget that they need more clearance than standard pistons, so you may need hone work anyway to get the clearance set! So it is probably easier to rebore straight away, which seems a pity if the barrels really don't need boring!
You will have to decide you really want to spend that kind of money, and if you think you need the benefits? You don't need to.
