Topic: CB 500 57.75mm piston?

[streetCB]

Hi,

Wondering if anyone can shed any light on the type of pistons I am running in my CB 500. When I purchased the bike the PO said it had a 605 big bore kit in it. I have recently pulled down the top end to inspect it and fix a small oil leak. on inspection it looks good but is not stock. However its doesnt appear to have the 605 dimensions either. As far as I can tell from this site the piston OD is 61mm  whereas the piston OD in mine is 57.75mm with the bore measuring approx 58mm. This is an odd size? the biggest OEM overbore for standard 500  is 1mm which is 57mm and the base OD for the 550 is 58.5mm.

The piston and cylinders look good and I was hoping to go for a simple hone and new rings to accompany the new gaskets and avoid having to get a rebore and get new pistons as it was running 125psi and up on all cylinders. Does anyone have any clue about where I might find  suitable rings for this piston and cylinder diameter. Thanks

[754]

THIRD oversize for 500 is what you want .75 over rings.

[streetCB]

754,

appreciate the swift response but is that right? I thought 0.75 oversize would be 56.75mm? I hope you're right however.

[classic bike tuner]

meaybe a std 550 piston  58,5 mm

[754]

I think i read it wrong..read it as 57 being Std for 500.

[streetCB]

So this is the inside of the piston. Anyone recognise the brand of this mark?

[turboguzzi]

could easily be oversize pistons off some honda single, quite a common source for 500/4 pistons.

many people round here build 500/4 race motors with +0.50OS XL125S pistons = 57mm,

a +1.5 XL125S slug would be 58mm