Quote:
Originally Posted by Steve Arndt
Can you give a qualitative comparison of the old and new springs? Are they much stiffer?
Do you have your installed height number handy? I am curious and would like to compare it to my heads.
Steve
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Sure, you asked for it though
:
actually I also had a set of the old CB regular HD springs and they were about the same pressure at 10mm compression! (actually a tiny bit less, but that may have been accuracy or a batch or..):
10mm compression: 120kg from the CB650 outer spring
10mm compression: 130kg from the old (cheap) CB HD single(=outer) spring.
This made little sense, so I put the inner spring in also and got these results:
I use an installed type4 height of about 1,50-1,52" or ~38-38.6mm, which is a bit less even then T1 IIRC.
At installed T4 height I got 88kg ('seat pressure') with the dual CB650 springs.
10mm compress.: 177kg (which was not that much more comparively)
As I thought they might only start shining with higher lift cams, I got past my own '10mm reference' and measured also at larger compressions:
12mm compress.: 217kg (!)
15,2mm compr.: 228kg
which were somewhat the pressures CB advertises with, so I was happy after all
So the 'over the nose' pressure is fine with cams of about 0.500" lift which most of us use.
So much for my 10mm reference
Oh, BTW, the Gene Berg double springs that came off the engine after 2,5 season had a pressure of:
Installed height (T4): 61 kg
10mm compress. : 115kg (!!)
Now, I hadn't measured the GB's when new, but they are probably in the same range new as the CB's or Scat's. That means a HUGE reduction in spring pressure after my relative short milage and relatively mild cam (just 0.500" lift). This is about 35-40% loss after 2,5 season!!!
My Scat springs I had a few years ago measured 95-100 kg installed height and 145-150kg at 10mm compression when new, so they were even less then the CB's when new and showed 25% loss of pressure after 1 season !!
This led me to my conclusion: valve springs are wear items and most all are near junk to begin with!... Actually to be renewed after every season is the only thing to do. But what could you expect from 30-35 dollar spring sets...
I hope these CB650 (which are about 3 times as costly as the other springs mentioned, but still not really 'expensive') hold their pressure better.
Only one way to find out I guess...