ANSWER 24.

Loose tappets cause the valve to seat at a much greater speed than they were designed to.
Camshaft lobe profiles have an opening and closing ramp as part of their design. The purpose of these ramps is to soften the start of the lift of the valve and to soften the end of closing of the valve. If the tappet clearance is wider than designed the valve contacts the valve seat before the cam follower or bucket reaches the closing ramp. This means instead of the valve being eased on to the seat by the action of the closing ramp, seat contact is made while the follower is on the steep profile of the lobe. If left unattended serious valve and seat damage can occur. Valves can become stressed to the point where they snap at the valve neck. Pounded seats, mushroomed tips and tuliped valve heads can also develop from loose tappets over a long term.

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