Machining for dual valve springs

[RUSS74GHIA]

How do I calculate how much material to remove from the guide boss for the inner spring?

Is it simply a case of measuring the spring at full bind and making sure that when the valve is at full lift there is enough room?

For info cam is W-125 with 1.25:1 rockers.

[RUSS74GHIA]

Anyone?

[dangerous]

Most people only cut the diameter of the boss to suit the spring inside diameter,
(and to suit available shim diameters),
and down to the original spring seat depth.

You can then do a trial assembly with a light spring to determine the ACTUAL LIFT,
and then select the correct combinatin
of valve, springs, shims retainers and collets to give you the desired room to travel.

I always check the travel at final assembly,
to double check that you are installed at the correct height for maximum spring pressure,
 and with enough room to bind.