Author Topic: 1970 BSA B25 front fork oil seals  (Read 147 times)

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GeorgeGutowski

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1970 BSA B25 front fork oil seals
« on: 24 May, 2022, 00:27:14 »
When replacing front fork seals, does the bottom fork bearing bush need to be removed to get the dust excluder off? The bushes are in good shape - no play when I try to wiggle the stanchion inside the slider tube. Hate to beat the bush off and risk damaging the stanchion, especially if it doesn't need to be replaced. There is resistance when I try to slide the dust excluder through the top of the stanchion. I don't want to force anything without getting other opinions on how to take the dust excluder off. The oil seal is located inside the dust excluder and it doesn't look too difficult to replace the seal once I get the dust excluder off. Any help would be very welcome. Thanks.

spaceman

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Re: 1970 BSA B25 front fork oil seals
« Reply #1 on: 24 May, 2022, 06:41:01 »
As I understand it, the problem is that the stanchions have an increase in width where they are gripped by the lower yoke? Since you are replacing the seal, it probably doesn't matter if you slightly damage them pulling the chrome seal holder off via the top of the stanchion - I don't think you'll do any damage to the seal holder itself.

Once a seal is out, you can then work out whether it would be safe to re-assemble the seal holder from the same direction, perhaps using a bit of grease on the offending part of the stanchion to allow you to ease the seal past. Otherwise the bottom nut on the stanchion would need to be removed. The best way to do this is to clamp the stanchions back into the yokes (with spring removed) to stop them turning when you try to undo the nut.

GeorgeGutowski

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Re: 1970 BSA B25 front fork oil seals
« Reply #2 on: 24 May, 2022, 17:07:09 »
spaceman
Thanks for the quick reply. I did get the bottom nut off using a spanner that fit pretty close - think it's the one from the tool kit that adjusts the preload on the rear shock springs. You're correct, the stanchion diameter is slightly wider where it slides into the lower yolk - that's where the resistance is when I try to pull the seal holder off the top. I'll try "gently" pushing the seal holder past the ridge on the stanchion with a bit of grease - you're right, no point in worrying about ruining the seal since new ones are going in. I was worried about messing up the spring support and support washer, but it looks like there should be enough clearance. In case I do have to remove the lower bearing bush, is it a pretty tight fit on the stanchion? Just trying to anticipate what I may be in for. My workshop manual says the bottom bearing bush and damper shuttle are retained by the slotted nut. I got the nut off but the bush won't come off easily.

spaceman

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Re: 1970 BSA B25 front fork oil seals
« Reply #3 on: 24 May, 2022, 17:39:29 »
The bush is just a sliding fit but applying a bit of gentle heat will make it easier to remove. If you've got the bottom nuts off, it will be safer to re-assemble the seal holders back on to the stanchions from that direction.

GeorgeGutowski

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Re: 1970 BSA B25 front fork oil seals
« Reply #4 on: 24 May, 2022, 18:53:50 »
Got it off. Not as tight as I was afraid of. Thanks again for the advice.
Seals and O-rings ordered, bit of clean up, and ready to move on to the next chore.
FYI, bike's been sitting in my basement for almost 50 years - having a blast restoring it and learning about it. More sentimental value than anything else. With these old British machines, you either get it or you don't - guess I get it. I've restored 70's and 80's Hondas, Yamahas, Harleys(just a carburetor), and Kawasakis. This one's real special. Appreciate your help.