CB400/4 FRONT FORK REFURB BY JULIE

[Nurse Julie]

A slight diversion from the engine building today. On a couple of occasions the front forks have bottomed out and stayed stuck down momentarily. Also the forks seemed to be very hard to me on normal riding. Therefore decided to take them apart and refurb. I know many of you are expert with front forks but this is the first time for me doing this on an old Honda, so I thought I would share.

Here they are out of the bike.

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I took the top nut off with the air wrench.

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I also used the air wrench to remove the bottom bolt. This is an Allen head bolt, so needed an Allen bit, plus a little extension bar to get in between the studs. Before using the wrench I gave the Allen bit / extension bar a couple of good whacks with the big persuader.
Trig said it is always best to use the air wrench as this can prevent the part that the bolt is attached to inside, the bottom of the under seat pipe, turning with the nut.

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The old oil seal stop was then removed

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and then the old oil seal.

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The fork pipe was pulled out from the bottom case. The fork was then turned upside down to drain all the fork oil. All the internals were then taken out. The spring, the under seat pipe, the oil lock piece and the external drain bolt.
Every part was then cleaned thoroughly in solvent and dried. Including getting a long piece of stiff wire with a rag attached right down to the bottom to make sure all the old crud had been removed.  As Trig was doing some polishing at the time, he polished the bottom cases for me.

[Nurse Julie]

All parts cleaned and ready for reassembly.

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The oil lock piece was dropped down inside the fork pipe, then the new seal was inserted. A little red rubber grease helped this go in but even then it was still a very tight fit.

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The under seat pipe and the spring were inserted and the socket bolt re inserted and done up with the air wrench.

The under seat pipe

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All internals back in and showing the top of the spring.

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As this was a total strip down the amount of fluid to be put in is 160 to 165 mls. I wanted them on the softer side so went for the 160 mls.

The new seal in place in the bottom case with the oil seal stop in place and the fork pipe in situ.

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[Nurse Julie]

New O ring applied to the top nut and done up using a normal spanner.

All back together and standing upright for 24 hours to make sure there are no leaks. All copper washers were changed where necessary.

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A nice little job to do. I did find that I needed more than one pair of hands at times, so I got Trig to help.

[PatM]

Excellent photos- no reason to understand why the forks jammed down though.
the 2nd to last looks like the spring ring is displaced?

[Nurse Julie]

Excellent photos- no reason to understand why the forks jammed down though.
the 2nd to last looks like the spring ring is displaced?

I will check the spring ring Pat.

[Nurse Julie]

Excellent photos- no reason to understand why the forks jammed down though.
the 2nd to last looks like the spring ring is displaced?

I have checked those springs Pat and they are sitting OK. I went round them again though and tried to push them in further but still sitting in the same place. I'm wondering if it was the angle of the photo that made it looked displaced?.

[PatM]

Julie, you obviously know what you are doing, i have no doubt! As you say, the photo may have been viewed incorrectly by me- it was the 'springs' in the seals i was referring to- one seemed like it was trying to 'climb off' the seal.
Did you find anything that may have made the forks jam down?

I did my 400/4 seals ages ago due to the usual weeps/pits. Exactly the same as you- off the bike and tear-down.

I was alarmed at your engine/piston/head photos! and amazed it still ran!

[Nurse Julie]

Yes, it's those springs I have checked Pat. It's strange as if you look at the pic of the seals that came out, they look like they are sitting a bit scew wiff as well.
No, didn't find a cause for jamming down, it only happened a couple of times. I couldn't really measure accurately the amount of oil that drained out but it may have been a little on the low side. Anyway, it didn't do any harm stripping and cleaning and changing the seals, at least I know they are done.

[Nurse Julie]

Aaaarrrrh, Paranoia is setting in. Just checked them again and they won't seat anywhere other than where they are, so they can stay there. Paranoia moment over 

Thanks very much to the forum member that gave me the seals FOC.....you know who you are.

[kevski]

I have been watching this thread and i am impressed with the work you are doing Julie, and here comes the concern, you have just done your forks and i have looked at all the pictures and i see you have re-assembled in exact reverse of dis-assembly,  i rebuilt my 350f forks this year and they had never been off the bike, the difference is your seals appear upside down, this not only exposes the coiled ring to atmosphere and the possibility of rusting out but the chance of oil bypass and out of the top of the seal, i have replaced a lot of fork seals over many years and never seen them this way up, so unless this is a trick of the light or you have special seals, you need to replace the seals the right way up.

[JamesH]

Have to agree with the above Julie. I think the seals are in upside down....the open 'spring' side should be facing the medium its trying to seal...

[Nurse Julie]

Well Kevski , thanks so much for your input and your concern and now I'm really worried. Yes, I put them back on the way they came off with the spring facing upwards. I will have to look at some pictures and speak to Trig later, to see the correct way up. I assumed they went that way, as like I said, that's the way they come out. Also, if they were supposed to be fitted 'spring' facing down, how would you know the spring was in the correct place, or even there at all and not fallen down the fork?. I will report back.

[Nurse Julie]

Thanks as well James, I'm on the case 

[Nurse Julie]

By what I have found so far, yes, it looks like I have them in upside down 
In the Shop Manual is says 'press fit the new seal, using seal driver part number blablabla' I am now thinking that if I had put the seal in the other way up and used a seal driver, which I didn't, the driver would then make contact with the 'flat' side of the seal and not the side with the recess and the spring in. No wonder I found them so tight to get in !!!
No worries, I will just have to do it again, the right way up. I will show it to Trig though before I take them apart and start again. Learning curves.......don't you just love em. Thanks to you lot for being so observant, what would I do without you.

[taysidedragon]

I suppose it's a lesson to all of us. Never assume that the old parts were fitted correctly in the first place!
Even factory original parts can be fitted wrongly.