1982 CB750C fork oil conflicting fill amounts?

[deeveeance]

Quick question so I can finish the forks on my 1982 Honda CB750C Custom.

Just got progressive springs from the VintageCB750 website, and cut spacers to length to match stock. Also had them powdercoated black.

I have a Clymer's book that only states 155cc of fork oil is needed, no indication as to drained or top off value.

Other searches here (and Google) with supplemental workshop PDFs have 245cc drained/225cc fill.

My forks are Air Assist as well, if that makes a difference.

Intuition is telling me to go with 245cc, but just thought I'd double check.

 

[deeveeance]

Looked through Clymer book again, found another set of fill values (172-177cc).

First two images from Clymer, third from PDF shared around here, addendum workshop manual.

 

[SenseAmidMadness]

I would aim for the lower of those numbers, 180ish cc, with the tighter-wound side of the Progressive springs mounted downwards in the fork leg. The Progressives will displace more oil and may create a similar oil level as the larger cc amount would with the stock springs.

However, I'm no expert. What I do understand is that you're not usually aiming for a given capacity with damper rod forks -- you're targeting a specific level of fork oil below the top of the fork. The factory service manual gives you a volume measurement that will achieve that oil level with a completely stock fork. When you modify things, the ideal volume measurement changes. You can find the right spot by measuring with a dipstick, and you can also adjust oil level if you pour too much by using a syringe, a sharpie, and some vinyl tubing.