Fork Seals

[McCabe-Thiele (Ted)]

I know we call them rubber seals, I suspect (as we know)  they are primarily a type of plastic, perhaps more modern fork oil contains the plasticisers to keep them supple?

Although I didn't use ATF in mine, the later ATF's definitely contain plasticisers to keep seals supple.

[Otis]

I know we call them rubber seals, I suspect (as we know)  they are primarily a type of plastic, perhaps more modern fork oil contains the plasticisers to keep them supple?

Although I didn't use ATF in mine, the later ATF's definitely contain plasticisers to keep seals supple.

I think that is so very true. When having reached a certain age and having dealt with older technology it's easy to overlook the very significant improvements in materials and fluids.

[Bryanj]

At a certain age ALL fluids are a problem!

[Oddjob]

I’m trying an experiment with my 550 fork seals. For some reason the space left by Honda is deeper than the fork seals they used. So that meant either a gap above or below the seal and the circlip holding it in place. Didn’t seem right to me so I looked around and found some genuine Honda seals that were the same external and internal size but were wider in depth. Seem to remember it was an off road bike and not imported into the UK so I was forced to source some in the USA. Not tested them yet but they are double lipped as well.

Oh and they come with a spacer as well, so I can fit the standard seals if I want but with a spacer underneath. Seems like a result.

[Bryanj]

Ken, i seem to rememberreading somewhere that the height of seals changed, 13mm and 11mm come to mind but dont quote me, maybe check the veru old 750 parts book in Ashs stash(ex mine)

[Skoti]

I’m trying an experiment with my 550 fork seals. For some reason the space left by Honda is deeper than the fork seals they used. So that meant either a gap above or below the seal and the circlip holding it in place. Didn’t seem right to me so I looked around and found some genuine Honda seals that were the same external and internal size but were wider in depth. Seem to remember it was an off road bike and not imported into the UK so I was forced to source some in the USA. Not tested them yet but they are double lipped as well.

Oh and they come with a spacer as well, so I can fit the standard seals if I want but with a spacer underneath. Seems like a result.

Aye,

Same with me, changed mine recently and noticed the gap above the circlip.
According to P.O. It still had the original seals.

Fitted genuine Honda seals but gap still exists.
Strange.

[Oddjob]

I’ve checked the parts books Bryan and I cannot spot any changes to the seals. They start off one size and they stay the same size till the model is discontinued. And yet as Skoti says there is a gap between the seal and the retaining clip. That worried me a little, could the seal be moving up and down inside the fork slider? Over time would that become a problem? Why had Honda not fitted a deeper seal or just cut the clip groove just above the seal to stop it moving.
So I started looking at it and I think you’re right, they started saying fit 750 seals instead but they appeared to be the same size, maybe the 550 ones were single lipped and the 750s were double, I managed to source some which I thought might just solve the problem, they are thicker but they also came with a spacer, which made me think why didn’t Honda just fit a spacer in the first place? Then I got sick last year and that was that. Only remembered it yesterday.
I do remember thinking last year, IF I do fit a spacer where is best, below the seal or above. Both positions have merit. My thinking is below is best but maybe I’m wrong. Any thoughts?

[McCabe-Thiele (Ted)]

I fiiltted the deeper seals on my 500 as sold by Pyramid.

My 400 forks had been rebuilt  by the PO, I did not know the 400 had a similar design.
 

[K2-K6]

There's quite a lot of detailed development in MTB forks that could be of interest.

This just one of them https://www.totalbleedsolutions.co.uk/products/skf-dual-fork-seal-kit-fox-air-34mm-fn-mtb-for-mountain-bike-mtbdual34fn?variant=54135620370817&country=GB&currency=GBP&utm_medium=product_sync&utm_source=google&utm_content=sag_organic&utm_campaign=sag_organic&gad_source=1&gad_campaignid=22869149694&gbraid=0AAAAAoPeQzp8BD-xWIRj6jLI41b5-lR1y&gclid=CjwKCAjw7KvTBhA6EiwAWnutYdWoxqC34bAZgie_1IuIx-NxXFLh-yXPBoN0fZrAl9X2QZqRaV_q2xoCUE0QAvD_BwE that gives a view. They ordinarily list the sizes in technical specifications, so finding a match could be possible.

Whether there's equivalent in size (particularly of OD) I've not specifically looked. I work on them in various diameter up to 40mm stanchion size, they cascade downward from there, through 38, 36, 35, 34 etc.

Many use a serviceable foam wiper ring above the seal and under dust cover that catches dust etc.

As I've put on here before, favour Motul fork oil for both lubrication and choice of specific viscosity to match need in getting good response and damping characteristics. 

Most of the MTB stanchion are high strength aluminium, with hard anodised coating. Focus on not scratching that, along with low stiction is high on agenda in that field.

[K2-K6]

This one give seal comparison in chart

https://www.scribd.com/document/556118464/DimensioniSeals

[Oddjob]

What size were they Ted?

The problem is that we’d prefer to fit genuine Honda seals if at all possible but that can be a problem as afaik only one bike had them fitted as it’s been obsolete for years. Plus it was a USA bike generally and even finding someone with stock left was difficult. I think I bought the last few sets they had listed last year. Had them posted to Roo when he was over there. The spacers though IF they cure the problem can mean we can fit the standard seal, which is great as I have a few sets of those.

[Oddjob]

A lot on here Nige have had fork stanchions hard chromed, which as you know is self lubricating and low stiction. Which should help matters I’d imagine.

[McCabe-Thiele (Ted)]

What size were they Ted?

IIRC I initially fitted DS seals to the 500, I did not like the huge gap between the retaining clip and the top of the seal. I fitted the Pyramid ones as they showed the depth as 13/14.5 mm.

I did not record the brand of seal that Pyramid supplied , they were made in Japan the part number was FS-032 they were 35x48x13/14.5 mm, still a gap but much less.

https://pyramid-parts.com/products/motorcycle-fork-oil-seals-pair-35x48x13-14-5?pr_prod_strat=e5_desc&pr_rec_id=601a58d40&pr_rec_pid=9006093861209&pr_ref_pid=9006091960665&pr_seq=uniform

[Skoti]

Got to mention, the original seals on my F1 were a really tight and difficult to remove.
Had to use a heat gun and gently work around then with a blunt tyre lever to get them out without damaging the stanchion.

Similarly the new seals were a really tight fit, used a seal driver and a plastic mallet because I was afraid of damaging them.

Maybe Honda decided the circlip is not for seal retention but added safety?   

[Otis]

I noticed that on full left lock the indicator on my fork cover just touches the fuel tank whereas on full right lock there is a good half inch of distance before reaching the tank.

Is this normal? Visually everything looks to be correct but it feels to be wrong.

Also, I noticed that the slight seepage of oil is appearing on the bottom of the rear axle holder nut on the RHS. Is this where a failed fork seal leak would likely manifest itself?

Thank you