Valve Spring Ground on the Outside Why?

[MadBill]

That could account for the grinding. Mitsubishi is unknown territory for me but it sure doesn't resemble a pushrod American engine part. it has twice the coils and about triple the wire diameter of a typical inner; looks like the stress would be very low.

[Nefario]

Since the spring rate is function of wire diameter to the 4th power, even a small change in wire cross section area will have a substantial impact on rate, seat force, and nose force.

Yep. The square wire (it was rolled this way, not ground) can have a higher moment of inertia (as in BENDING moment of inertia) and be a stronger spring in the same space as round wire. Square-ish may be easier to manage in the spring winding process as well.

[MadBill]

That one looks more like a die spring.. https://www.google.ca/search?q=Die+spri ... 85&dpr=1.1

[DaveMcLain]

That one looks more like a die spring.. https://www.google.ca/search?q=Die+spri ... 85&dpr=1.1

It sure does..