Author Topic: 77 CB550K Fork Rebuild  (Read 414 times)

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Offline Maraakate

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77 CB550K Fork Rebuild
« on: July 20, 2022, 09:36:08 AM »
Hello,

Both forks are really starting to weep so it's time to change the seals.  I have all the parts, read the FSM many times over, and have looked around on here and other places for advice.  I think I can do this job just fine on my own.

However, before I get started I will need something to drive the seal in.  What's the proper size PVC Schedule 40 pipe you guys are using so I can run out and get this before I start tearing things apart?  Failing that, what size of the motion pro fork seal driver tools would be appropriate to use?

Thanks!
1977 CB550K
1979 CM400A

Offline Bankerdanny

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Re: 77 CB550K Fork Rebuild
« Reply #1 on: July 20, 2022, 01:21:38 PM »
The fork tubes are 35MM OD if I recall correctly, which is about 1 5/16" so 1 1/4OD pipe should work. In my case I have a 30MM socket that I use.
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Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Maraakate

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Re: 77 CB550K Fork Rebuild
« Reply #2 on: July 20, 2022, 01:25:10 PM »
I just measured the total size of the seal it's 48mm.
1977 CB550K
1979 CM400A

Offline ekpent

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Re: 77 CB550K Fork Rebuild
« Reply #3 on: July 20, 2022, 03:04:38 PM »
In a pinch you can use an old seal as a driver of sorts which is what I usually do..
« Last Edit: July 20, 2022, 03:12:51 PM by ekpent »

Online bryanj

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Re: 77 CB550K Fork Rebuild
« Reply #4 on: July 20, 2022, 03:40:25 PM »
1 1/4 is smaller than 1 5/16 so would go down the inside of the seal, you need something near to the od of the seal
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Offline Bankerdanny

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Re: 77 CB550K Fork Rebuild
« Reply #5 on: July 20, 2022, 06:09:31 PM »
1 1/4 is smaller than 1 5/16 so would go down the inside of the seal, you need something near to the od of the seal

You are correct sir. 1.5" is probably a bit too small even based on the seal design.
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline Maraakate

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Re: 77 CB550K Fork Rebuild
« Reply #6 on: July 29, 2022, 10:33:01 AM »
I just went ahead and used the old seal to drive the new one in.  Placed a block of wood on top of the old one after I cleaned it and oiled both seals with some of the fork oil and drove it home.

I put 145cc in there, I forget where this number came from but it was marked on my bottles for this project.  Probably read it on here, somewhere, at some point but I don't remember.

With that said, I looked at the books and there is conflicting information.  FSM says about 160cc in one place, 185cc in another.  Clymer has the same silliness.  OM said about 155cc if I remember correctly.  Is 185-190cc the correct amount to pour in when completely draining the forks and the ~160cc is when doing regular maintenance to swap the fluid?

I also have a fork oil gauge tool.  Have not used it before, but if this helps accuracy I could use that instead.  Mine is 1977 so not sure if things changed between years.  Forks work better than they ever have, and no more leaks so I'm pretty satisfied; but would like to have the proper amount in there.
1977 CB550K
1979 CM400A