Chain Tension

[Littlewheels]

Just putting engine back together and fitted the chain but 80 link is too tight with only 3mm movement at most and feels notchy when you turn crown wheel and was only just able to fit.
I had noticed this when I stripped the engine down (been rebuilt before?) so I bought an 81 link chain but this is the opposite and too loose?
Both chains are IWIS so not sure what to do apart from change the 81 link for another 80 link and see it it differs from the old one?

[Warkton Tornado No.1]

Sounds like you'll have to use a pull down chain tensioner. Good Luck with choosing one. Whenever I've worked on an engine fitted with one, I've had to re-engineer them....

[Littlewheels]

The two chains do differ -they are both marked Iwis but the markings on the tight chain look a little less prominent so maybe its a counterfeit/copy? I know Iwis use holographic packaging to help prove authenticity and this usually happens because someone has tried to copy the product.
Decided to go with a second hand Regina extra chain off eBay described as showing no perceivable play so i'll see what that's like.

[Fast n Furious]

Don't expext too much from a Regina chain.....They are very elastic