Topic: fork seal thickness

[webby645]

Hey guys,

Im restoring a CB750 K2, the original forks are destroyed. The replacement forks i've acquired are slightly different (I believe they were from late '72 onwards- drawing attached) and im in the process of fitting new seals.

the problem i have is that the only replacement seals that i can find are 11mm high, but the actual height of where the seal sits is more like 15mm??? when i disassembled them there was no spacer/washer in there. as far as i can tell everyone uses 11mm seals on these, but if i put those in, there will be a 4mm gap in between seal and circlip. note there is no bushing or anything else in the forks that i have (like there is in the original 72 model forks).

any guidance on this appreciated.

webby

[Dream750]

No worries. You can install the thicker (double lip) seals as shown in this service bulletin:
 
http://manuals.sohc4.net/CB750SB/750_41.pdf
 
These genuine Honda seals are still available, PN: 91255-341-305 and the size is: 35 x 48 x 13.2
 
David Silver Spares UK and USA also carries this thicker size, but they are aftermarket.
 
Welcome to the forums.

[brewsky]

At least one aftermarket brand is supposed to float in the seat area...don't know about any others:
http://forums.sohc4.net/index.php?topic=111091.0;nowap

[PeWe]

No worries. You can install the thicker (double lip) seals as shown in this service bulletin:
 
http://manuals.sohc4.net/CB750SB/750_41.pdf
 
These genuine Honda seals are still available, PN: 91255-341-305 and the size is: 35 x 48 x 13.2
 
David Silver Spares UK and USA also carries this thicker size, but they are aftermarket.
 
Welcome to the forums.

Thanks for the part number of the higher seal 91255-341-305 that David Silver still has!!  I have leaking forks direct after replacement.

New fork tubes and new seals but pissing oil....did not do that before with old forks from 1976 and 30 year old seals. I might have mounted the new seals wrong.

I cannot understand why the thinner one, 11mm is the recommended in all lists without an extra back-up ring to fill the gap.
Even for my CB750K6 that is the newer one relative the bulletine. 11mm is the old seal.

Double lip seal must be better as the old Honda bulletine inform about. This is my 3:rd set.
Now in bike: CycleX leaking (mounted upside down?)
Have in garage. New Honda 11mm   91255-KBH-003
Today ordered: New David Silver 13mm  91255-341-305

[mcswny]

No worries. You can install the thicker (double lip) seals as shown in this service bulletin:
 
http://manuals.sohc4.net/CB750SB/750_41.pdf
 
These genuine Honda seals are still available, PN: 91255-341-305 and the size is: 35 x 48 x 13.2
 
David Silver Spares UK and USA also carries this thicker size, but they are aftermarket.
 
Welcome to the forums.

Thanks for the part number of the higher seal 91255-341-305 that David Silver still has!!  I have leaking forks direct after replacement.

New fork tubes and new seals but pissing oil....did not do that before with old forks from 1976 and 30 year old seals. I might have mounted the new seals wrong.

I cannot understand why the thinner one, 11mm is the recommended in all lists without an extra back-up ring to fill the gap.
Even for my CB750K6 that is the never one relative the bulletine. 11mm is the old seal.

Double lip seal must be better as the old Honda bulletine inform about. This is my 3:rd set.
Now in bike: CycleX leaking (mounted upside down?)
Have in garage. New Honda 11mm   91255-KBH-003
Today ordered: New David Silver 13mm  91255-341-305

Interesting, the 76 forks shouldn't need the backup washer or larger seal? I thought after 74 they did away with the extra space?

[PeWe]

I'll come back with photos when I change the seals. How the old were installed and the new thicker.
Same with dust caps same height as the 51425-375-003, my old were higher and looked better. New a little bit too tight. Maybe I'll reuse my +30 years old ones. Rubber not cracked. My old must have been for another bike when CB750K never had them from the beginning.

It might take 1 week or so. I'll install oil cooler at the same time, 4-1 off, bike raised with jack to remove front wheel and lower forks complete with fender, brake....

[PeWe]

No worries. You can install the thicker (double lip) seals as shown in this service bulletin:
 
http://manuals.sohc4.net/CB750SB/750_41.pdf
 
These genuine Honda seals are still available, PN: 91255-341-305 and the size is: 35 x 48 x 13.2
 
David Silver Spares UK and USA also carries this thicker size, but they are aftermarket.
 
Welcome to the forums.

Feedback here as promised.
Dream750: Thanks again for a very good advice.
I bought the thicker fork seals from David Silver UK. When I installed them I felt a Déjà vu
Exact as I remember when I installed fork seals 31 years ago (and removing the stiff b_stards  . ) Same model of seal, heavy and stiff.
I oiled with fork oil all over and hammered them down with my nylon sledgehammer. I used a KM Socket 46mm OD to hammer down with (the tool I found, a tube of 46-47,5mm thickness 2-3mm will work, important to not harm the upper lip). The oil made them easy to seat within a few heavy strokes with the heavy hammer.

Why sell the crappy 11mm low fork seals when the bigger one is MUCH better??
Correction: The bigger one seals, the other not. I'm sure that there are plenty of leaking forks out there.

I could not see that I had mounted the other 11mm version upside down, lips faced against the oil. Cycle X seals. I ordered HONDA OEM from Germany but they looked the same. Also delivered without washer.

No doubts when I got the bigger one from David Silver.
http://www.davidsilverspares.co.uk/parts/by-part-number/partnumber_91255341305/
Easy to understand how it should be mounted. There is a small lip around the fork tube facing upwards as can be seen in the Bulletin and photo below. No leaks
The old small ones leaked direct even without driving the bike.