Peugeot Simplex rear derailleur upper spring tensioning

[zhang]

I'm reassembling an old Peugeot bike which is fitted with Peugeot branded simplex derailleurs. The rear derailleur looks like this (but much dirtier!):

http://i.ebayimg.com/t/Peugeot-Simplex- ... ~60_58.JPG


I can't figure out how to tension the spring in the upper pivot as it seems like the short end of the spring which attaches to the hex bolt (not the longer end that attaches to the derailleur body) is slipping. Can anyone explain how to tension the spring and which way that teardrop shaped washer which has two tabs differently sized tabs facing in opposite directions is involved?

Failing that, can the derailleur be re-assembled correctly without fitting it to the bike? If so, I may just take it to the LBS.

Thanks!

 

[zhang]

Here are the actual parts in question.

 

[47p2]

It could be that the end of the spring has broken off causing it to slip