Showa SBK fork bottom & slider question

Started by junior varsity, May 17, 2011, 04:11:42 PM

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junior varsity

I believe this to be a straightforward question:

Is the fork slider threading & diameter the same on 848 Showa forks and 916-era (40mm mount) Showa SBK forks?


I'd like to swap fork bottoms so that I may use the forks I have currently in my garage rather than buy a replacement set... This is going to sound odd at first, but I'm interested in taking a set of 848 forks and switching the radial fork bottoms (I know, go "backwards in time") with a set of 40mm axial/conventional brake mount fork bottoms from a set of 916 Showa SBK forks. 

This will save me the expense of finding good condition forks like that, and really only having to find a 916-era set with decent condition bottoms - It may seem like a step backwards in time, but the rest of the intended bike's set-up uses old-era parts: billet 30/34 "GP" calipers, 6-bolt/320mm/10mm-offset rotors, cable driven speedo, etc - and I already have the 848 forks.

ducpainter

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junior varsity

Not interchangeable so I learn.

.MS characters chimed in over yonder - its a no go, partly due to valve adjustment being on the side rather than through bottom.   Apparently the 65mm mount bottoms such as on the 749/999 can't swap onto the 916-era 40-mm mount bottoms either for some reason.   Which I took to reiterate the need for the 65-to-40mm adapter plates for those wanting to run better calipers before radial mounts became available (Brembo 40mm GP 2-piece and monoblocks, etc).

DarkStaR

#3
Quote from: j v on May 19, 2011, 05:38:18 AM
Not interchangeable so I learn.

.MS characters chimed in over yonder - its a no go, partly due to valve adjustment being on the side rather than through bottom.   Apparently the 65mm mount bottoms such as on the 749/999 can't swap onto the 916-era 40-mm mount bottoms either for some reason.   Which I took to reiterate the need for the 65-to-40mm adapter plates for those wanting to run better calipers before radial mounts became available (Brembo 40mm GP 2-piece and monoblocks, etc).

I did try to find info on this just because you posted, and one thing I found that makes the 749/999 "seem" not compatible was the different offest of the caliper mounts, but then again I have no FHE. I "think" the mounts are 5mm wider on either side = 10mm wider apart total.

ducpainter

Quote from: j v on May 19, 2011, 05:38:18 AM
Not interchangeable so I learn.

.MS characters chimed in over yonder - its a no go, partly due to valve adjustment being on the side rather than through bottom.   Apparently the 65mm mount bottoms such as on the 749/999 can't swap onto the 916-era 40-mm mount bottoms either for some reason.   Which I took to reiterate the need for the 65-to-40mm adapter plates for those wanting to run better calipers before radial mounts became available (Brembo 40mm GP 2-piece and monoblocks, etc).
I'm thinking the 40 and 65 mm bottoms not being interchangeable is incorrect.

I'll ask someone who knows for sure.
"Once you accept that a child on the autistic spectrum experiences the world in
 a completely different way than you, you will be open to understand how that
 perspective
    is even more amazing than yours."
    To realize the value of nine  months:
    Ask a mother who gave birth to a stillborn.
"Don't piss off old people The older we get, the less 'Life in Prison' is a deterrent."



Speeddog

You *may* be able to swap the complete lower and tube.
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junior varsity

#6
 "What if" time...:

I am considering/hoping to use cartridges... A la traxxion / ohlins / etc...

Would it still matter where lower adj is located? Don't some have all adjustment at top?

hackers2r


junior varsity

Right, I thought I had remembered one of them (if not more) did, but if the fork bottoms wouldn't work on the good condition 848 forks' sliders & tubes it won't matter much.

hackers2r

Well the main problem I see with using non adjustable fork bottoms on tubes that were intended to have adjustment is that there's going to be a hole somewhere that is open. I may be wrong though. In my mind, I too think it'll be easier to swap the entire bottom, slider and all.

junior varsity

?

Uh, these are adjustable fork bottoms - both the 848 and the 916

So no, the hole will be plugged with the normal adjustment mechanism - just as when the cartridge would be used in either the 848 or the 916 fork.   I don't know where non-adjustable fork bottom came from.   



The slider tubes screw into the fork bottoms (Example of DLC coated sliders above, threaded end in distance). The adjuster is located ON the fork bottoms. The adjuster is simply located in different places on the 848 fork bottom than on the 916 fork bottom.   The goal of using the 848 fork sliders (and tubes) is to have the newest and most pit-free version I can. Pitted or worse still gouged fork sliders affects sealing and stiction.

My interest in using the fork bottoms - transferring the 916 fork bottoms over - to the 848 forks I already have is to be able to use some higher spec calipers along with the rotors and wheel/speedo that I already have.  If the cartridge forks where one controls rebound, other controls damping, and all adjustments are made from the top, this may problem solve an otherwise incompatibility between 916 fork-bottom and its damping adjuster with the 848 Showa fork's OEM internals (since they'd be removed).


Here's a blown-up view of an Ohlins fork (gas charged) and I understand it to show one fork where it would be either rebound or separently compression (the two valves are located in the middle - one goes in one fork, the other valve goes in the other, adjustments made at top - just like the 30mm kit)