help me out my modem loose lock

Find the satellite again and get back to the 16.5 reading or better.

Then try tightening the clamp bolts slowly and carefully.  It is quite normal to lose the signal at this point since tightening the bolts will alter the pointing.  Tighten gently and progressively, adjusting the pointing as required to keep peaked up.  Once correctly pointed pushing on the dish should cause no movement at all.  A rigid mount is critical.  You need to get to the exact centre of the beam.  Just good enough on receive will not do, as the transmit beam is narrower than the receive beam.

Having found the satellite it is often best to peak up in azimuth, tighten the azimuth clamp, then peak up the elevation last as tightening the azimuth clamp will often increase the elevation angle sufficiently to lose the satellite.

Adjust the polarisation also.   Rotate the feed either way till you lose lock (probably +/- 45 deg or more).  Then put to the centre point.  The polarisation tilt angle of the LNB/BUC may alternatively be determined by calculation and set approximately using the scale on the feed throat.

If your receiver loses lock on the receive downlink signal for no apparant reason check the F connections.  Waggle the cables.  The centre pin of the F connector should stick out about 2mm and the outer braid must make good connection also.

Best regards, Eric.