Topic: Are these springs stock for a 77 CB550K?

[phalenor]

In the process of replacing the springs in my 95% stock 77 CB550K with a pair of Progressive Suspension springs, I noticed the old springs appear to be progressive rate as well. This bike has had two POs before me, and sat in a basement from about 1982 until I acquired it in late 2012.

Were the stock springs on the 77 K3 progressive from the factory? Was that a common aftermarket upgrade perhaps?

See the attached photo. The new PS spring is on top, what came out of the forks is on bottom. They differ in length by 1/2".

Any reason not to go with the new PS springs?

[flatlander]

Any reason not to go with the new PS springs?

yes if you prefer the magical mystery of a spring of unknown origin and quality and that may have sagged over the years (see how it's shorter than the new one - you could measure it to see if it's within specs but then you still don't know if it's the original honda spring) 
 

[phalenor]

The only specs I have found dictate a minimum length of something around 16". The old springs measured 18-9/16", the new PS springs measure 19-1/16".

That being said, the old springs had practically no preload when I removed the cap bolt. I had to work to reinstall the bolts with the new springs, so I think this will be an improvement.

[Duanob]

Were the stock springs on the 77 K3 progressive from the factory?

Yep.