G'day Speedy and folks,
If the carbon deposit extends down the piston skirt like that, the rings are knackered! Despite what thickness they are - they can lose their spring tension too. For the little that they cost, just replace them.
In addition, by far the best tool for scraping carbon out of ring grooves is a old ring broken in half, with the end ground to a chisel edge.
For scraping off carbon, you need a tool with a bit of length to it, to make it easily controllable. So a razor blade isn't the go at all.
Something like an old wood chisel, for scraping the gasket remnants off flat surfaces, works well.
And a flat tool, with a square ground edge, for piston crowns and such - I make these from sections of power hacksaw blade.
I'll put up a few pics, if you like.
Speedy, what's the serial number stamped into the RHS of the crankcase? That lower half crankcase has the integral bottom seal protector, which is later than 1971.
