Thanks guys,
I really feel priviledged at receiving all the advice.
It turned out it was not the magnet after all but bulge on the pan below the crown wheel(it was at the same height as the tyres)It prevented the rear wheels from gripping the surface on certain sections of the track.Three strokes with a needle file and Jim Clark in his Cortina is setting records .....
Keep the finger on the trigger
Cheers and