This is the fourth season on my solid roller set up,limited street use and 4-6 times to the track.It's a Scott Brown cam mid 650's lift Comp lifters and Harland rockers, when should I think about having them rebuilt or replaced?

I go by the lash changes. If you see a change of more than .003, better find out why. You should probably check it often now. Like Mike said, it depends on ramp rates and how well the valvetrain has been controlled by the springs. It wouldn't hurt to check spring pressures on the weakest ones, if you have the tools. I have a Manley tool that goes over the rocker arms and uses a torque wrench to check pressures. It can't give you a perfect number of pounds, but will show if they are all close or if there is a weak one.

I currently have 335 1/4 Mile passes on my Springs and lifters. Rockers have more than that. Valve Springs still check good and lash hasn't moved so I haven't bothered to change anything. It will come apart for a freshen up this winter.

Cam is 278/284 .619/.641
Comp Lifters
Comp Springs
T&D rockers

Thanks to all,just a little uneazy after seeing my buddies boat motor bust a spring that broke the cross bar for the lifter that in turn spun killing the cam.

Not science, but...
Rotate the rocker and tappet wheels over with your fingers. If:
you can rock the wheel sideways at all, or
if there is a tight spot, or
any up-&-down play, or
it feels crunchy..

it's toast.

ive been using comp cams springs and roller lifters for a while , i change the springs and lifters every 3 years , last year i went 5 years on them and i had 2 lifters getting crunchy but the comp 943 valve springs are perfect i did drive a lot on the street 5 yrs is about 3500-4000 miles for me