Does anyone know what the largest dia valve spring that factory 416 or 041 heads can be machined to fit?
I have a set of each of those heads and I'd like to use one of those sets, along with some larger dia springs if possible.

Thanks

 

there isn't any real limit. they can be opened up to fit about anything you can find. 1.5 being what most people would open them up to.

 

As usual, ede is right. I don't question him, but n case you do, here's some evidence. The last set of 14014416s I worked up were opened to 1.480", and there was room for a lot more spring if necessary: