The problem is as much with the lifters as with the cams.

The OEM lifters have a very hard skin which is not very

thick on the surface that rides on the cam. If you find an

OEM lifter that is anything but dead flat and shiny, you can

pretty much count on the cam being damaged. Once the

skin wears through, the edge is hard and sharp and is almost

like a cutting tool on the cam. The hardest area to keep

lubricated is the cam/lifter interface because it is mostly a

line contact with very high unit pressure.

A check on the cam is to put a ruler longitudinally

on the peak of the lobe in question. If it is at all

rounded lengthwise (doesn't touch the ruler all the

way across) it has started to go. I think this problem

was worst in the mid 70s but have also seen it in

B18s. Do NOT under any circumstances try to

"save" a damaged lifter. It will only destroy your

cam.

Also cams may go in anywhere from a couple minutes to

several thousand miles depending on condition of lifters

and driving circumstances.

Re: valves too tight -

They may be OK after being run "tight" too long but

chances are good that if you tear it down, you'll find

pits or cracks in the seating area of exhaust valves

run without enough clearance. May run OK for quite

a while. Once you get a crack, though, it is a tiny

flame passage during the combustion stroke, so it

will indeed get bigger and worse and continue

to cause the valve to run hotter than it otherwise

would.