Author Topic: Fork oil seal questions  (Read 418 times)

Offline Rudgeman

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Fork oil seal questions
« on: 20.05. 2019 11:04 »
Hi, I've stripped the forks of my recently bought '61 Super Rocket to cure oil leaks. I found some scores on the otherwise new looking stanchions and grit in the oil.Despite this the bushes seem to fit ok, although also scored.

So I bought some seals, ckeaned everything out and reassembled. That's when I discovered the new seals don't fit the seal holders.The seal holders are stainless and the seal bore is 45.0mm diameter. I thought this was unusual given the stanchions are imperial. A close inspection of the seals I took out reveals them to be 45.0 x 32.0 x 7.0. That makes them a good fit in the holder but a very poor fit on my stanchions (which I measure at about 1.248" or 31.69mm). No wonder they leaked and let in grit.

The replacement seals are 46.52mm OD or 1.831".

Questions :
1. Is the 46.52 correct or have I been sold the wrong seals ?
2. How can I identify the maker of the stainless seal holders ? Presumably they had access hybrid metric / imperial seals. I can't find any that are 45.0 x 31.69 x 7.0. There's no markings on them.

Any help you can offer would be greatly appreciated,

Kerry
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Online JulianS

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Re: Fork oil seal questions
« Reply #1 on: 20.05. 2019 11:31 »
My old Payens catalgue gives the seals as 31.7mm ID x 46.61mm OD x 9.5mm wide. Which is the same as my spare Pioneer and Weston seals.

My spare oil seal holder has oil seal housing 46.4 mm diameter.

So badly made oil seal holders.

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Online RDfella

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Re: Fork oil seal questions
« Reply #2 on: 20.05. 2019 11:34 »
I have stainless seal holders on a couple of my bikes (can't recall where I got them from, but can't be many suppliers) as I got fed up with replacing rusting ones. Have to say they're not perfect, but as far as the seal bore is concerned, usually the seals are a pretty tight fit as they pass through the threads of the seal holder, so is there a reduced diameter above that? If there is it could be turned out.

PS my seals fitted OK, although one leg leaks from the thread.
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Online Black Sheep

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Re: Fork oil seal questions
« Reply #3 on: 20.05. 2019 14:04 »
I had the same problem. My seal holders came from HT engineering. I was able to source new seals online. Can't remember details but when I get a moment, I'll nip up to the shed and find out.
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Offline Rudgeman

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Re: Fork oil seal questions
« Reply #4 on: 20.05. 2019 18:36 »
Thanks to you all for your useful contributions. I'm convinced rhat whoever made these particular stainless seal holders decided to make them compatible with the closest equivalent metric oil seal, rather than for the BSA, imperial oil seal. They're probably cheaper and it makes it easier to machine the seal recess - because it's slightly smaller than the ID of the threads - but it compromises the seal's fit on the stanchion.


I've dug out my old large chuck, spent a couple of hours getting it cleaned up, fitted and centred and have now bored one of the holders out to fit my correct seals. When I did this it was clear just how close to the thread diameter I had to go with the boring tool. I'll now have to make a tool to enable me to tap these seals home with some sealant behind them.


Never a dull moment eh ? And to top it all - these newish stanchions have the transitions to the slightly larger diameter where they clamp in the yolks machined with a sharp corner - so the seal won't slide over them. They should have had smooth rads and chamfers. Twenty minutes with a dremel has sorted it but it makes it very clear what a wide range of quality there is in the parts out there for these popular bikes.

Thanks again for such prompt and helpful replies.

Rudgeman
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Online JulianS

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Re: Fork oil seal questions
« Reply #5 on: 20.05. 2019 19:58 »
To fit the seals in the holder just push them in with thumbs as far as they will go then screw the holder and seal onto the fork bottom, the seal will be pushed in square.

Fit the seal and holder from the bottom of the fork stanchions not the top or the seal will likely be damaged.
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Online Black Sheep

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Re: Fork oil seal questions
« Reply #6 on: 20.05. 2019 20:20 »
The seals you wanted are 32x45x7 (though I fitted 32x45x8 double lipped in preference). £2.12 +VAT each from Simply bearings. Easier than hours of machining...
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Offline Rudgeman

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Re: Fork oil seal questions
« Reply #7 on: 20.05. 2019 20:57 »
Hi Black Sheep (Baaaaaa ?),

Yes I realised I could source replacement seals the same size as those I took out, and at very low cost. My concern is that they are not the right fit on the stanchions. At 32mm, they're 0.3mm bigger than those intended for the 1.248" stanchions. That means the lip is not squeezed onto the stanchion's surface as hard as intended and that's bound to compromise sealing both in and out. I have lots of grit removed from the oil as testament to what got past the seals going in, and oil in the seal holders as evidence of oil like that leaked out.

If the stanchions are machined well to provide smooth, gradual transitions to the slightly larger clamped diameters, there should be no damage from assembling the holders from the top. However, the examples I have were not.

It's all a learning curve.

R
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Online Black Sheep

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Re: Fork oil seal questions
« Reply #8 on: 20.05. 2019 22:15 »
One reason I opted for the double lipped seals. I have never found seals that could be fitted from the top in many years of riding and working on BSAs. Funnily enough, the supplied seals with the stainless holders lasted well with no ingress despite much use and abuse - many miles covered, several Beamish Trophy trials, far too much winter and bad weather riding.
One thing I did was to check the dimensions of standard BSA replacement seals. Also metric. Hmm. 
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Re: Fork oil seal questions
« Reply #9 on: 21.05. 2019 03:21 »
I have been to the pub *beer* *countdown* many moons ago---about 35+ years  my old fella[BLESS HIM] made me the bushes to fit the new stanchions { out of his precious lead bronze----,it was precious because he borrowed it from work before I was born, maybe thinking it might come in handy one day}. I took the stanchions to work to get them chromed {thankyou national coal board *yeah* }on the top to just below the bottom egg yoke,  I gave instructions and even taped them off where I wanted the chrome to end. they came back{ free of charge } CHROMED ALL OVER *rant*----proper good old fashioned hard sod off CHROME! so pops had to ease the bushes out, any turner will agree he wasn't a happy bunny,but all went well. you lot have done really well getting this far so now I will get to the point, I rammed my seals over that step on the legs and they have never leaked...….moral of story get CHROME err is that something to do with computers too *sleepy*
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Offline Rudgeman

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Re: Fork oil seal questions
« Reply #10 on: 22.05. 2019 16:50 »
Hi again - quick update. I modified the seal holders to take the 'std' seal (at least a seal with the correct OD - I'm pretty sure it's also a better fit on the stanchions than the old seal. All back together again - seems to be ok.

The proof of the pudding is whether it leaks or not. Time will tell - I'll update this thread either way.

R

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