Check your worm drive fittings.

This part is one of the most overlooked parts on the downtube with a lot of wear and tear.
Link to changing your cogs:
• Changing cogs on a Hei...
Link to parts needed #8:
shearingworld....

[@robertking8807]

I took the down tube to the shearing centre and its come back that on the short down tube there was not enough oil on the section and it was causing a dry spot and they said that's what causes it to come free from the top off the down tube which I wouldn't have though off