Reface the seatings on a valve grinding machine equipped with a collett if such a machine is available. The seat angle is 45°.

An alternative method is to hold the stem carefully and as close to the head as possible in the chuck of a lathe or drilling machine, being careful not to mark the stem or otherwise damage it.

The valve head may then be cleaned and polished up with ordinary emery cloth, a fine grade being used for finishing purposes. It is desirable to true up the valve seats before grinding in the valves because although a valve is a comparatively cheap replacement it is necessary to avoid wearing the seats in the cylinder head by prolonged grinding as they are expensive to replace.

It is unlikely that the seatings in the cylinder head will require truing up with a cutter unless the machine has covered a considerable distance.

If recutting is needed see Page 40.

If the seats appear to be in reasonably good order, the valves should be lightly ground in. To grind in the valves, use a very fine emery powder mixed with oil or paraffin, or one of the numerous brands of valve grinding compounds. These compounds are sometimes put up in double-ended tins, the coarse compound in one end and fine compound in the other. It is very seldom necessary to use the coarse variety on the valves. Use as little compound as possible smeared over the seating on the valve. Avoid getting any compound on to the stem or into the valve guide.

Slip the valve into position and hold the end of the stem near the cotter groove with a suitable holder which should be tightened on to the valve carefully to avoid damaging the stem or the edges of the cotter groove.

Rotate the valve backwards and forwards, maintaining the Valve head in contact with the seating by pulling lightly on the stem. Lift the valve frequently from the seating to prevent the formation of concentric rings and bring it down into another position, recommencing the back and forward movement for a further period.

After a few minutes light grinding the holder should be removed and the valve taken out. The compound should be wiped off the valve and off the seating in the head. The seatings should be a light grey in appearance, free from marks or black pits. As soon as a light grey seating is obtained all round the seat of the valve and all round the seat in the head, the grinding-in operation is complete, and the other valve should then be tackled.