Bad cam

This is probably a stupid and obvious question but.....What is the easiest way to tell if a cam is bad in an engine?

 

measure the lift at each valve with a dial indicator. if you take your reading at the pushrod or lifter multiply by the rocker arm ratio and compare to the cam specs. you're looking for consistancy so if you're results are not what the spec is but consistan your cam is probably ok. cams don't often go bad in normal use. is there a reason you suspect the cam is bad ?

 

Is it a small block Chevy, or Cadillac HT4100 cam? They used to drop dead all the time. Pull the valve covers, turn the motor over and look at the rocker arms make sure all are moving and should be moving about the same amount.
Bad cam symptoms: Low power, dead skip on one or more cylinders, low compression on those same cylinders, backfiring/ popping in intake or exhaust and of course valve rattle because of increased valve to rocker arm clearence, if you have hydraulic lifters and had to re-adjust the valves because of rattle it is a good bet the cam is wearing prematurely.

 

well, there's no EASY way, as you have to see the cam at least, so valve cover has to be removed.
both posters are right. in a bad cam, one that has worn out lobes, you can, actually, see the wear. when you turn the engine(always turn in clockwise direction!!!!) and watch the cam lobes, you might see groves carved in the lobes, or ridges, depending if the rocker wore it out flat or in some areas only. cams are normally softer inside and very hard on the outside, a thin layer of steel highly saturated in carbon, and if it is worn through, you'll see dark grey area where the rockers did it.
at some point in wear, lifters can not accomodate it anymore, with symptoms as described in the other post.