Shimano Tourney mec problem

[ren531]

Can anyone please help me with this issue I have with replacing a worn out rear mec on my son in laws bike. The nearest replacement I found to the original seems to have no spring mechanism on the pivot where the mec bolts on to the frame and does not tension the chain, am I missing something either from the mec itself or from my lack of dealing with newer mecs in general.

 

[Cycleops]

There is no spring in the mechanism on the top half where it bolts to the frame, this is only a hinged parallelogram to allow it to travel across the cassette. The tensioning mechanism for the chain is in the lower half behind the upper jockey wheel. When fitted before you thread the chain it’s pulled back as shown in your pic. You should be able to pull it down and forward, you’ll feel effect of the spring there.
The chain will pull it forward when fitted.

 

[ren531]

I have fitted it fully to the bike and could not get it to tension the chain at all, including winding up the adjustment screw to max, I think I will refit it and study it some more, I must be doing some thing wrong. I have lots of older similar mecs that all have a spring tensioner on this pivot so not sure how this works