SOHC.co.uk Forums > CB500/550

Piston Rings

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s7paul:
Hi All,

My CB500 was bored 0.5mm oversize many years ago.  I haven't been happy with it recently, and have stripped it down.  The piston to bore clearance is more than I'd like and compression was well down on 2 cylinders, so I've decided to get it taken out to +0.75.  I've sourced a set of NOS pistons and 2 sets of Honda rings from an eBay seller, but had to get the other two sets of rings from DSS.

My concern is that the rings from the eBay seller are different to the DSS rings.  The top ring looks the same. The second ring of the eBay set has a step in one side (so the outer part of the ring is thinner).  The oil control ring is solid, whereas the DSS rings are 3-piece.

So, my questions are:

Are the eBay rings REALLY old stock (before 3-piece oil rings became the norm)?

and

Would the eBay rings be OK to use?

Any/all advice would be appreciated.

s7paul:
Thanks very much.  That's interesting, as mine came from..........Stoke!  And yes, the part number on the box is -014.  If anything, I was more bothered about the step in the second ring, as it's something I hadn't seen before.

The received wisdom on t'internet seems to be to bore .0008" to .001" larger than the pistons.  At the moment, I can get a .0025" feeler down the side of some of the pistons (it's fairly tight, but even so).

ka-ja:
I was always told that the compression ring with the outer edge step went in the top groove, the step was to avoid any small wear step in the cylinder bore top.

s7paul:
The top rings are identical in both sets (with a small chamfer on both outer edges).  The position of the T mark on the stepped rings is such that the step is on the bottom side when fitted.

Edited to add: A bit of searching has revealed that the stepped second ring is called a Napier ring.  I'd never heard of it before.

ka-ja:
Just had a look at some nos Honda CB72 rings, looks like top ring champhered edges, middle ring outer step to the bottom, both rings marked tp  for top, my original thoughts were for "Cord" rings for worn cars. And yes the two top rings are different colours as already stated.

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