I dont know anything about isuzu 4cyl engines, but do they only have 1 spring per valve? My '72 yota started breaking valve springs around 230k miles but they have a smaller inner spring. Still made lots of noise but kept the spring keepers in place so it never dropped a valve. If the stock heads only have one spring you might check to see if any of the head remans add a 2nd spring.

--Dave

1999 Rodeo LS 3.2 4x4 5 Speed
32x11.50-15 BFG T/A KO on US Wheel 94 series
3" Lift - Rancho 9000x
Rear No-Slip Locker
Flowmaster 50 series SUV 2.25"

There is a very fine line between "hobby" and "mental illness." - Dave Barry