CB900FD forks

[AndyD]

Hi,
Been away from the bikes for a while but trying to tidy up a few projects to at least stop them perishing slowly through neglect!
First up is a CB900FD from 1983 which I bought many years ago from the original owner that has been standing around since about 1989.
The PO had stripped the forks for some reason he couldn't quite remember, failed to fix whatever was wrong and loosely reassembled them to the bike before laying it up for a very long rest.
Now I've finally got the bike on the ramp and got it all apart again it's a bit mysterious - some parts missing, some wrongly assembled and some a bit damaged.
I think I've figured out most of the issues but what I can't grasp is that the internal damper assy isn't held inside the fork stanchion in any way - all other bikes I've worked on you could only pull this out through the top but here it can slide right out either end.
Not sure if the stanchions are wrong or I'm missing something so wondered if anyone had any ideas / experience?
Cheers,
Andy

[Bryanj]

Have you tried looking at a parts diagram, cms possibly

[AndyD]

Hi Bryan,
Spent a happy few hours scanning the microfiche in the other day so happily now have full parts details and diagrams for the bike.
I've worked out the parts generally and know what's missing but the bit I couldn't fathom was what if anything retained the internal damper assy.
On other bikes I've worked on this could only be removed from the top of the forks - once slid down inside it would be trapped at the bottom and then the damper is bolted to the underside of the fork leg with an allen key bolt.
Here I can slide the assy in and out top and bottom which seems odd.
I'm not sure if this is correct or if something is wrong with the parts.
Cheers,
Andy

[Laverda Dave]

Hi Andy.
I remember that CB900 sitting in your garage when I visited you and it was patiently awaiting it's time on the restoration bench.
Is this the winter project and did you finish the second CJ250 you were working on?
Dave

[Bryanj]

I cant find an 83 FD on CMS but the 82 FC has the same cap screw up wards through the slider into the damper

[AndyD]

Hi Dave,
Hope you're doing OK.
Yes, that's the 900 sat in the corner waiting patiently for some attention!
Pretty well finished the CJ360T, just needs tweaks and tyres to be roadworthy.
Spent some time doing the XT250 which is also now complete and I really need to get it out on the road to run in as it had a rebore and full rebuild after finding endless bodges and damage on close inspection.
Really should catch up some time if you're around.

Cheers,
Andy

[AndyD]

Thanks Bryan,
It's odd but the FD version doesn't seem to appear in a lot of parts lists etc. for some reason.
The FC is very similar and luckily I've also got the microfiche for the FD so have scanned that in which is really useful.
I think I might have worked out what's wrong after a closer look this morning.
[ Guests cannot view attachments ]
It looks like part 17 should be fixed in the bottom of the fork tube (pt 7) but it looks like it's actually stuck in the bottom of the fork case (pt 14).
This means that the damper (pt 23 etc) can just pull straight through the tube and nothing holds the tube and  case together if that makes sense.
I'll try and get one out later and see if I'm right - never seen this before and always thought that part was 'fixed' inside the fork tube somehow, but maybe it's just just pressed and can come apart with force.
I think the PO maybe just forced / abused the fork assembly until something gave way and came apart, then couldn't figure out why it wouldn't go back together and partly / loosely reassembled it.
Hopefully nothing is damaged
Cheers,
Andy

[Bryanj]

Looking at that parts pic i dont think the damper should not slide out of the bottom of the tube, i wonder if the po has got some "different" fork tubes that physically fit but are not right.
As far as i can see there is nothing stopping the sliders falling off the tubes if you raise the bike high enough, especially with air pressure in the forks.

Even if the lower bush is held by circlip it only stops at top bush and that is a lot of travel and would expect damper to come out.

Is it possible there should be a lip on lower bush to stop damper?

Just thinking sideways now

[AndyD]

Hi Bryan,
I had another closer look at the parts and also Googled images etc. and I think part 17 is in the right place in the bottom of the slider as the hole through it is too small to slide up over the damper assy.
Like you I can't see what would stop the damper pulling straight through which is what's thrown me - every other fork tube I'm familiar with has something at the base which only allows the damper assy to come out through the top of the tube.
Looking at the fork tube parts online at CMSNL / Ebay there doesn't seem to be anything at the bottom of the tube to retain the damper.
The only other thing that could keep it all together maybe is the top fork bush which is then retained by the ring and circlip up by the fork seal.
I'll try a quick assembly this afternoon and see if that works as I can't think of anything else so far.
Cheers,
Andy

[McCabe-Thiele (Ted)]

That arrangement looks very similar to my 400NA Super Dream front fork arrangement, mine was the early version with no oil drain screw.

IIRC the bottom plunger was secured by the bottom Allen key bolt.

[Bryanj]

What holds the bottom bush, 11, onto the tube?

[AndyD]

The bottom bush sits in a recess in the fork tube so is positively retained - it's a split bush so once inside the tube it's closed.
However my idea that maybe that would prevent the tube coming up too far isn't right as the top bush is right at the top of the fork leg so this would only prevent the tube coming out very late, so the damper could clear the base of the fork tube by this stage.
I'll try and Google some pictures of the inside of a fork tube for this model as I really can't get my head around it at the moment and just wonder if maybe there was something in the fork tube that's been removed somehow and lost - would be very odd but i can't currently think of anything else!
Cheers,
Andy

[Murf]

I have a pair of Honda CBX Prolink forks I am rebuilding (slowly). They are air forks and  i am pretty sure they are the same sort of design as the CB 900, but with larger 38mm diameter stanchions, Though that will probably depend on cb900 year. They don’t have the useless antidive mechanism so if yours do this post will not be relevant to you.

I will try to get the parts together (been apart for a while) and take a photo so you can see what should be there.

[AndyD]

Thanks Murf,
The forks are 39mm with the anti-dive assy so I guess might be different to the CBX ones.
After another exhausting (boring!) Google I finally found a picture of the end of a standard fork tube.
Bizarrely it does look like the PO may have somehow removed the internal end bit inside the tube that retains the damper
[ Guests cannot view attachments ] is the picture of an original NOS one
[ Guests cannot view attachments ] is how mine look
No idea why or even how they would have removed the internal bit but it would explain why it feels / looks wrong as they are.
More hunting now to try and track down some replacement fork parts I guess!
Cheers,
Andy

[andy120t]

...I'm just trying to remember my forks from an old bike, doesn't does 42 screw into 17, ,(42 from the bottom/outside the fork - and 17 is inside) and that's what holds it all in?