Unless new valves are being installed then the ones removed should be refitted back into their original locations. Where feasible, apply molybdenum disulphide, or some other anti-scuffing paste, to the valve stem to limit the early wear in the guide. Install the valve in the guide, install the oil ring along the valve stem and then install the spring and spring collar with the close coils of the spring against the head. Then place the compressor of the valve spring with or without the spacer tube and with great care squeeze the spring, taking care not to have the spring flying out, as it will tip in squeezing up, and this will make it difficult to fit the split collets. Squeeze the spring to the extent that it will reveal the grooves of the split collets. In the event of tube method, insert the split collets through the tube slot with a screwdriver, greased, to collect the collet and then place it with the narrow end facing down. The second half can be challenging because the spring is not centrally spaced about the valve stem, which can be mitigated through numerous measures by paying careful attention to tipping the spring with the compressor or pre-exerting a little more compressive force. After the split collets have been correctly aligned on the grooves of the valve stems, carefully disengage the compressor tool, without pushing either of the collets out of place. The two halves of the split collet should be in contact, when disengaged, and otherwise one of them might not be seated properly in the grooves. Do the same with each valve individually.