Reading a little between the lines, a cutter is good for softer seats and a stone essential for hardened seats? So presumably the cast iron seven block valve seat can be cleaned up with either?
Yes Nick, that is how I would approach it. But as Ruairidh says, take care, the stones can remove a surprising amount of material in a surprisingly short time.
The Repco branded 'vibro-centric cutter' I am familiar with drove its stone through a coil spring inside its housing to impart a reciprocating action to the stone [this action was adjustable by twisting the end cap] to avoid cutting concentric tracks- does the SP/B & D one do this? Also with the Repco kit, once one had cut the seat, the instruction was to chuck the tool in the valve grinding machine by its pilot [which was a solid pilot] and finely dress the seat stone against the valve refacer wheel, using the same angle setting on the machine as the valves had been faced to and a final light cut taken. If the kit was in good order [particularly the pilot] you could get pretty good results without any lapping, even 3-angle if you had the inclination.
Edit: forgot to say that for the Repco variant the pilot was locked in the tool and rotated in the guide, iirc their theory was a snug fitting rotating pilot would average out any minor valve guide wear and keep the seat concentric...
Yes Nick, that is how I would approach it. But as Ruairidh says, take care, the stones can remove a surprising amount of material in a surprisingly short time.
The Repco branded 'vibro-centric cutter' I am familiar with drove its stone through a coil spring inside its housing to impart a reciprocating action to the stone [this action was adjustable by twisting the end cap] to avoid cutting concentric tracks- does the SP/B & D one do this? Also with the Repco kit, once one had cut the seat, the instruction was to chuck the tool in the valve grinding machine by its pilot [which was a solid pilot] and finely dress the seat stone against the valve refacer wheel, using the same angle setting on the machine as the valves had been faced to and a final light cut taken. If the kit was in good order [particularly the pilot] you could get pretty good results without any lapping, even 3-angle if you had the inclination.
Edit: forgot to say that for the Repco variant the pilot was locked in the tool and rotated in the guide, iirc their theory was a snug fitting rotating pilot would average out any minor valve guide wear and keep the seat concentric...