Questions about Mamiya Press 65mm lens

I just received a Mamiya Press 65mm lens and if any of you have experience with this lens--I have a couple of questions. Does the aperture open completely when the lens is wide open? On my lens, when the aperture is opened to f/6.3, the iris blades don't open to the full round diameter of the lens elements--they stop short and form a pentagon--is this normal?

The helical is also very stiff. I imagine the grease has dried out and needs to be replaced. Has anyone ever disassembled the 65mm (or other) helical, cleaned, relubed, and successfully reassembled it? Thanks.

Barry

I've noticed on some of my Mamiya RB67 lenses that wide open is actually stopped down a bit when I press the DOF preview lever or dry fire them. I thought this a bit odd but never asked anyone about it... I have a 65mm but the old RB67 65mm Sekor may be a completely different beast to the Press version.

Yes, this is normal. Although the aperture can potentially open wider, Mamiya apparently deemed the performance wider open than f6.3 not up to par, so the opening is limited by a stop on the aperture mechanism.

Thank you both. I've been having less than stellar luck with my used equipment purchases lately and that's one less problem to worry about.

Enjoy it - I find the 65mm to be a very nice lens!