Twin track engineering , need say more,
Valve Lapper set for hand lapping valves of all type of cups upto small and large valves. You lap valves to make valves seat like new again.
when the valve is closed and theirs not a perfect seal you loose compression. Lapping the valves restores this. So is a must have any mechanic or DIY enthusiast.
Place valve lapping compound on valve seat or surface as directed by compound instructions. Install valve in to valve guide press correct size suction cup firmly on to head of valve lapper tool handle between palms of the hand until suitable finish is obtained.