Technical Thermostat flap does not close

[Piet59]

Hello, after assembling the box with (non original spring) thermostat (see picture) and the attached flap, this flap only fully closes with a little helping hand. I could not tighten the nut above more tight. After that I replaced the spring thermostat by an original one. It seems the problem of the not fully closing flap still exists: about 1 cm remains open (see picture). I dare not tighten the nut more in order not to damage the thermostat by overstretching it.
Could anyone tell me how to deal with this?

 

[Piet59]

Should it perhaps be like that? On Youtube I saw ‘the 500 workshop’ and while James, the host, was explainingthe engine i saw the flap of his engine in the same position as mine. See attached picture

 

[lazylobster]

Mine too does not fully close.

 

[Piet59]

Cheers