3AJ swing arm/rear suspension query

[cabron]

recently i noticed a problem with the swing arm on my 3AJ - the chain was resting on the top of the swing arm and there was a lot of slack in the chain. i thought that if i increased the tension on the chain the chain would be lifted clear of the swing arm, but it is actually the positioning of the swing arm in relation to the sprocket that seems to be causing the problem.

i suspected that the rear shock had collapsed and removed it, but upon closer inspection the mono shock seemed to be fine.

someone suggested to me that it might be the swing arm linkage bearings which might have seized up, thus preventing the mono-shock from expanding to its intended size. does this sound reasonable?

has anyone experienced this problem before? any advice would be much appreciated.