OK, yeah I checked the oil pump and it wasn't that. I thought it was something aroun the timing belt. So what's involved with replacing it? The engine runs quite smoothly (car isn't moving or anything, just starting engine with car on blocks) so I'd say the timing belt is ok. If this spring was missing, would the timing be off heaps or would the car still run ok?
And to replace it, is it basically replacing the timing belt tensioner or can it be re-installed without replacing the whole unit?