I brought two blue orb and i install it on the v5500 and it seems a little over size.After switching on my computer for about 15mins,i touch the back of vsa100 core...and it felt damm hot and and scource my hand.And i would like to know whether is it over heating?

Hm, if it is too hot even to touch, this is definitely Overheating.

Note that not all Orb Coolers are suitable, sometimes the Stock Coolers are actually more efficient.
(It might also indicate they have simply not been properly installed, leading to a severely decreased top-side cooling, effectively overheating the VSA beneath)

I generally never saw any Point in modding a Voodoo4/5 with other Coolers, unless Problems were already experienced..
(some cards seem to have a fairly low quality in the way the Coolers were attached, sometimes leaving a visible space between the actual Cooler and the Chip, however)

The stock coolers do the job, but they are very noisy with those two small fans whizzing away at high RPM.

Any heatsink works by conducting the heat away, so if the chips are too hot to touch, then I guess either the heatsinks are undersized (unlikely) or you haven't mounted the heatsinks onto the chips correctly.

How did you mount the heatsinks? Are they stuck on with a self adhesive pad? Or did you glue them on with a two part heat conductive epoxy?

There are no mounting holes on a V5500, so unless you have fashioned a custom mounting solution, any other kind of fixing is out.

Basically you need to ensure that as much of the heatsink is mounted onto the chip as possible, and that the heatsink is flat and square on the chip.

Andy

Checking it out,i see that the orb is not making maximum contact with the chip,and i superglued those orbs to the chips.i tried testing out for artifacts but i dont seems to get them even like after 5-6hrs of usage?So should i stop worrying?

this might be allright, but be careful..another system fan should be added..