[russell_ram]

To quote Myles,

'No advantage unless you are running very heavy valve springs and high revs. There is a disadvantage if they are heavier than standard because they add inertia which will cause standard springs to 'float' sooner.'

I would add

The only time I could think you might want to use them with hydraulics is if you've modified you head so much that you can't get in the acceptable (say 20-60 thou) range with std rods. You're pretty unlikely to need their additional strength or rev capacity with a hydraulic cam in any case.

Russ

ps I'm pretty certain in the factory not a single engine was ever checked for lifter pre-load prior to being despatched - the tolerances on the std Rover parts are such that the pre-load will work every time.