64 283 with low compression

[Jmageee902004]

I did a compression check on my 1964 283 and it seems that every cylinder seems to have low compression ranging from 60-90psi. Is their a way to find out if its the valves or rings that have gone bad without taking the heads off? I don't want to take apart the engine just yet because it runs and drives and i don't want to take it out of commission. Plus im not to the point of taking apart engine for rebuild just yet anyways, im just looking to the future.