Topic: Help identifying 61mm pistons in CB500 to find rings

[betterthanurs916]

So my father and I have recently acquired a 1971 CB500, essentially for free.  The story is that the guy who owned it used to drag race it, but got killed in a street accident on another bike in the early 80s.  Anyhow, it has been sitting since 1983.

It has a hot cam with no identifying marks on it, some fairly serious port work, and 61mm pistons in it.

They look like CB750 pistons that have been lightened, but there are a few markings on them that suggest they aren't Honda OEM.

Anyhow, one of the compression rings is broken and we are trying to get a proper replacement.  I think OEM Honda 750 rings will be the ticket, but I wanted to check here first in case anyone has any other information.


Notice deep cuts on the skirt


"300" on the side like the K0-K5 750 motors




I don't think Honda pistons have these markings.







No circlips for piston pin, just these pin snubbers...seems odd to me.


So? Any thoughts? My guess is aftermarket, Japanese made OEM replacement pistons that were machined to work in a CB500....but perhaps these were something more unique than that.  Any information appreciated.

[754]

Might be Powroll?

[Jerry Rxman Griffin aka MuthaF'er]

If they are 61mm and the ring lands are the same width as 750 pistons then just order from Honda. Nice deep valve pockets for big bump stick 

[turboguzzi]

could be great to see some pics of the bike, porting, etc. specially since it sounds like a bit of an untouched  time machine. Teflon buttons instead of circlips are common practice in race motors, no clips to jump out of place
Those pistons look like an early attempt at a slipper piston but as a minimum, would check those narrow tongs for cracks. If you are not going to race it in anger and just want to do demonstration passes, would fit more normal pistons. Nut fun having a small piece of piston drop off in the motor
BTW, those supper wide valve cuts are not needed in a 500. unlike the 750s the valves in 500/550s are central/symmetrical.