Replace Piston?

[darnjr]

I'm doing my second top end and I'm not sure if I should replace the piston or just the rings. The first time I did a top end there was evidence of major blow-by, a lot of brown areas below the rings and the underside of the crown was brown in color. The piston I just took out looks perfect with the exception of carbon build-up on the crown that I could clean off. I was going to go ahead and replace the piston, pin, bearing and circlips but I don't want to waste money on a new piston if I don't need to. Is there a measurement I could take on the piston or would it be safer to just go ahead and replace it? I use stock pistons in case it makes a difference.
Thanks
DA

 

[yzbluebeast]

If you're going to do a top end you should measure the piston(with a micrometer, 90 degrees to the pin and 10mm from the edge of the skirt) and cylinder bore.(with a dial bore guage) Look up the spec for piston to cylinder wall clearance.
You want to be sure the clearance is still in spec.

 

[darnjr]

The ring/groove clearance is .076mm and the difference between piston width and bore is .025mm as I've measured it. My owners book does not specify the piston diameter to bore measurement so I'm not sure if it is in spec or not.