Hello Geoff,
Are you using a good mercerised thread, remember that Singer machines were made to take Sylko number 40 and 50 and trylco 60, to use other makes of thread is not a major problem but you will have to watch those tensions, if you have a plastic bobbin case commonly known as an appolo which should be black, if it is grey you have the old style, just check it to make sure there are no burrs on, check those tensions if the problem keeps happening it could well be the machine is out of time.
Ken, e-mail any problems
drivewithken@blueyonder.co.uk
August 2007