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You can but most don't. It's not that expensive to upgrade your heads with new, stronger valves and re-use the springs. If you are going to re-use the valves, just make sure you lap them in (assuming they are in decent shape).
Tamra
Building 818SR #297 picked up 10/25/14 with Andrew (xxguitarist)
First start 12/21/14, First "drive" 1/17/15
First Dyno at EFI Logics 3/7/15- 310whp at 15psi for break in, full spool by ~3500rpm!
First autocross 3/29/15
1st Registered 818 in Connecticut 7/24/2015. 9 months - 1 day from kit pickup!
Common problem in the 2.0 heads, usually from over tightened spark plugs. The 2.5 heads have plugs with nearly twice the thread length and do not crack as often.
Wayne Presley www.verycoolparts.com
Xterminator 705 RWHP supercharged 4.6 DOHC with twin turbos
Take them to your local machine shop and have them check the heads out to make sure they don't leak if they don't your golden
I have the same problem, if you check my build you will see the same pictures. My motor had over 160,000 and chances are they have been cracked awhile. I checked that they didn't leak, lapped the valves and used the heads as is. I think worst case is a valve seat drops. My engine is back together and running well but I only have a couple of miles on it and maybe 4-5 hours of running time. I would bet that if you were to look at most 2.0L out there you would find the same issue.