Topic: CB750K0 Front Fork Seal Backup Ring Required???

[markb]

I'm replacing the seals on my forks and for some reason the backup rings, part number 51452-319-000 (goes between the circlip and the seal), were missing.  The problem is they are no longer available and I can't find them anywhere.  It seems like they would help keep the seal from distorting.  The circlips are discontinued too but I think I found some at Ohio Cycle.  So, my questions are:
1. Can I (should I) get by without them?
2. Anyone know why I can get some?
3. Does anyone have one they could measure, probably is a standard size bearing spacer.  I also have access to a machine shop so I could make some.
Thanks for any replies,
Mark

[bryanj]

Not 100% sure but i think the new seals are thicker and dont need the backup rings

[jmk]

Here is a service bulletin (PDF) for the K1 and K2 750, where the new seals are indeed bigger and you don't need the backup rings.

http://sohc4.com/tiki-download_file.php?fileId=34
or the webpage where it was found if that doesn't work:
http://sohc4.com/tiki-list_file_gallery.php?galleryId=2

Although they don't mention the K0.  In fact, maybe this post is completely irrelevant and I never should have written it.  Oh well.

Hopefully someone else can tell you for sure.

[Johnie]

Mark...I just did my KO fork seals and there were no backup rings on mine.  My build date is 1/70, so that is how I put it back together without the backup rings.  I can not see anything that the backup ring would have done that my circlips did not accomplish.  In fact, if I had the rings on mine I think I may have had some trouble getting the circlips in place once the seal was installed.  Your new seals should have the double edge seal on the inside lip which were better than the originals. 

[lordmoonpie]

Isn't the idea of tha backup ring on the K0 forks to also act as a hard surface in rebound? Because the damper rod screwed into the fork lower is not captive in the stanchion like it is in later models, the fork bush is located directly under the fork seal. I'd guess that rebound forces pushing up will pressure the fork seal and it will only have the circlip to act on to hold it in place and stop it distorting. The backup ring must provide extra resistance to any distortion forces on the fork seal and also covers more of the seal face...hey just a theory 

The circlips are standard so you can get them from a good machine shop as you can the internal circlips for the lower fork piston. The spacers are all discontinued and I managed to get the last 3 at my stockist for my fork rebuild. Alternative is using ones from a breaker which are usually goosed anyway. I'll measure mine and let you know the size for the last one left!

[markb]

I think I solved the mystery.  I sometimes forget the best resource for discontinued parts - local dealerships that have been around since the '60's.  I imagine some of their parts have been on their shelves for 20 years or more.  I usually go to Service Honda first because their prices are better than dealers.  Anyway, I found the backup rings but they are too big in diameter and won't fit.  So I checked my K2 and they do have larger diameter lower cases.  After checking my parts book I see that the backup rings are for serial numbers 10039120 and above.  The service bulliten must include the later K0's and the reason the seals are bigger is because the cases are bigger too.  So the early K0's have the smaller seal with no backup ring.
Thanks everyone for your replies,
Mark