Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Otis on July 07, 2026, 10:45:57 AM
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On Sunday after a short run of say 5 miles and having met up with some guys it was noticed that my front offside tyre had some moisture streaks on it. Fork seals were mentioned and one chap felt around the lower end and said "yes definitely a weeping fork seal". Another chap said to wipe it all clean and see if it occurs again. Well typically, it hasn't occurred again after circa 60 miles of riding and everything is as clean and dry as a whistle as I write.
My only thought is that on the Sunday I recall hitting a quite depressed manhole cover and felt the forks bottom out; it was quite a jar.. Could it be possible that a significant compression like this could actually force a little oil past the seal or would the consensus be that it is likely that a seal is failing?
Any thoughts/guidance would be appreciated, thank you
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With correct amount inside nothing should come out on max compression
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Just keep a close eye on it. If the seals are leaking there will be a film of oil on the chrome stanchions just above the dust covers. If there is an oil leak on the bottom of the fork sliders it could be coming from the bottom fork bolt. Keep checking.
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Many many thanks for those two helpful replies.
I will monitor it closely but its slightly odd that the seepage should have occurred in a one off situation. Perhaps the seals are weak and perishing so whilst it shouldn't happen under max compression, perhaps it did and is a sign that they are going to fail soon.
From the records I have they were replaced 2000 miles ago but that was nearly 20 years ago!!
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Was it one leg or both? Worth lifting the dust covers to see what the condition is like underneath.
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Yes, in fairness it was just the one leg on the Offside.
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Was it one leg or both? Worth lifting the dust covers to see what the condition is like underneath.
Is that possible without dismantling the fork?
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Yes, dust covers should just pop up.
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This is still a bit of a mystery to me. Is there any way of testing the fork performance to see if they are as expected without having to strip down?
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Might be worth draining the fork oil, measure the volume from each side for comparison.
Check the condition, refill with correct volume of oil.
If fork oil is badly contaminated, be worth rebuilding them.
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Thank you.
Much appreciated advice.
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With oil in you can push down and see if there is resistance to travel both ways, apart from that no test.
Any leak of liquid is an mot fail, oil mist is allowed
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Personally when I was an MOT tester I’d most likely have failed it for oil mist, if it was enough to leave a ring I would have wondered how long that had been leaking like that and how much that loss of oil would have degraded the suspension. Saying that, I was a bit of a soft touch back then and I would have just pointed it out and said fix it asap. Depends how bad it looked.
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Personally when I was an MOT tester I’d most likely have failed it for oil mist, if it was enough to leave a ring I would have wondered how long that had been leaking like that and how much that loss of oil would have degraded the suspension.
Well, its progressing...
On my '00 ST both fork seals failed shortly one after another while up in Norway... they do have some nasty roads up there...
So I grew the routine of rinsing down rotors, calipers & pads with brake cleaner twice a day...
By the time we made it back home (Austria) both fork bottoms were FUBAR at the inside/bore... :-\
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Personally when I was an MOT tester I’d most likely have failed it for oil mist, if it was enough to leave a ring I would have wondered how long that had been leaking like that and how much that loss of oil would have degraded the suspension.
Well, its progressing...
On my '00 ST both fork seals failed shortly one after another while up in Norway... they do have some nasty roads up there...
So I grew the routine of rinsing down rotors, calipers & pads with brake cleaner twice a day...
By the time we made it back home (Austria) both fork bottoms were FUBAR at the inside/bore... :-\
They do sometimes just quit after looking and earning fine for many miles. Possibly through rubber ageing at a guess.
Think I'd have tried to make some little towelling catch devices to keep the oil from running down in that situation. A little like those Bjorn Borg era wrist sweat band things.
You'd need to stop yourself getting caught up in the whole headband and "Fame" type leg warmers though ;D ;D
With MTB forks (up to 40mm stanchion available) its considered reasonable to flip the bike (usually to install wheels after transit in car) and pump the forks a couple of times to keep the fork seals from running dry after storage period.
Difficult on a ST 1100 though ;D
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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.
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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.
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At a certain age ALL fluids are a problem!
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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.
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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)
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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.
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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?
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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.
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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¤cy=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.
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This one give seal comparison in chart
https://www.scribd.com/document/556118464/DimensioniSeals
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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.
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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.
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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
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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?
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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
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Rear axle nut? You mean front axle nut if it’s a fork seal. If it’s the 2 nuts holding the axle holder then there is an allen bolt hiding at the bottom of the fork slider under the axle clamp. There is a copper washer on the allen bolt which is meant to seal against oil loss. Either the bolt is loose or the washer isn’t crushed enough or it’s just missing.
Been a while since I worked on a 400 but aren’t the indicators on a small frame where the headlight mounts? Maybe the frame is bent or positioned wrong.
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Sorry, it was not clear, I mean't the rear nut of the front axle holder.
I have just checked all four nuts and torqued them to 25Nm and got nearly a quarter turn on each one.
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The nuts are only there to hold the axle clamp Otis. It’s the allen bolt underneath that is leaking any oil you can see, you need to fix that.
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The nuts are only there to hold the axle clamp Otis. It’s the allen bolt underneath that is leaking any oil you can see, you need to fix that.
Thank you for that, I will attend to it straight away.
Incidentally, here is a picture of the positioning of my front reflectors of which the left one catches the tank.
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Hi Graham,
Sitting on the bike with the front wheel dead ahead, does the headlamp seem to be pointing slightly to one side? Peer over the top to see relative to the front guard. The reflectors are threaded into the top shrouds, so that point is fixed however, the shrouds themselves can rotate slightly, causing your problem. Hence asking about the position of the headlamp. You can gently push on one side of the headlamp to make each gap equal.
Ian
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Incidentally, here is a picture of the positioning of my front reflectors of which the left one catches the tank.
Another possibility would be dinged steering limiters on frame head and/or lower triple...
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You guys are all absolutely brilliant and always enable a resolution/cause to be discovered.
The headlight alignment is spot on but I had overlooked the stops and just noticed that the RH stop lug had obviously sheered off in previous ownership. The stop lug looks like an integral part of the upper collar so I guess I will have to fabricate a replacement.
Thank you all so much for your guidance.
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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
Look at my reply#2. If there is a fork seal leak it will leave an oily film on the chrome stanchions and when it gets bad enough the oil will run down the back of the aluminium fork slider. If there is no oil there it is not coming from the fork seal!
Oil which is only at the bottom of the fork leg is coming from the bottom fork bolt. That is an Allen bolt at the bottom of the slider and hidden by the front spindle and spindle clamp.
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Don't rule out the fork leg drain bolt, it has a copper or alloy washer, easier to gat at than the bottom Allen key bolt.
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Many thanks guys for your tips and guidance and I shall check everything as per your advice. I may just replace the seals and oil anyway as I have already bought the kit.
Just going back to a point I raised earlier, I discovered that my RHS steering stop had sheered but I also noticed that next to it there is a threaded hole with nothing in it. I have attached a photo but am curious to know what it is for?
Cheers
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We all seem to have that threaded hole. There are theories about why it’s there but no one seems to know for certain. I think it’s there to accommodate a steering damper, maybe Honda were thinking of it at some point but fixed the problem some other way.
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I can't tell from your photo as it's a close up.
There is a thread on the underside where the loom bracket fits on the left underside.
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I have to say that whilst I had all sorts of worries about my fork seals leaking; after properly torquing the axle holder bolts to 25 NM which involved more than a quarter turn of each nut, I have not seen a single drip in a week.
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We all seem to have that threaded hole. There are theories about why it’s there but no one seems to know for certain. I think it’s there to accommodate a steering damper, maybe Honda were thinking of it at some point but fixed the problem some other way.
On the 400f. There is a kind of p clip that attaches from the underside to support the wiring going up to to the headlight shell.
Part no. 32123-375-000
[attach=1]
Regards
Dave
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On the 400f. There is a kind of p clip that attaches from the underside to support the wiring going up to to the headlight shell.
Part no. 32123-375-000
Another missing bit on my bike to replace then.... they keep coming! ::)
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Very easy bracket to make George and it stops the main loom hanging down in the breeze👍
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Very easy bracket to make George and it stops the main loom hanging down in the breeze👍
Turns out I did this a couple of years back. I seemed to be something different on here though. Steve at 400/4 bits got it for me,
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I think the OEM clip had a black vinyl dip coating, My one disintegrated long ago.
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I think the OEM clip had a black vinyl dip coating, My one disintegrated long ago.
Steve at 400/4 bits took the trouble to put a new one of those coatings on for me! ;D
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Plasti Dip is your friend - invaluable if/when refurbishing parts after blasting & coating & simple to use!
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Plasti Dip is your friend - invaluable if/when refurbishing parts after blasting & coating & simple to use!
I didn't know about it until you told me, probably going on my bucket list now! ;)
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Is this plastic dip something you can do at home?
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Something like plastidip, comes in a tin, just dip the thing in, allow the excess to drip off and wait for it to cure.
Difficult to justify a tin full of the stuff unless you have enough things to do, eg. Tool handles.
Regards
Dave.
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When I’ve done my rebuilds, to make the bendable metal OEM cable ties look as new again, I have them re-zinced at my local platers when he’s doing all the bolts etc (£50 a dip no matter how many / large the parts are).
I then use the heat shrink cable sheathing of an appropriate size to make them look nice. It just shrinks down, almost looks OEM and the surface is quite grippy.
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I've used Shrink Wrap in the past, I dont have enough bits left to jusify a tin of Platidip.
Good to know for possible future use.
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Bought a tin 10 years ago, used it a number of times since then on 4 rebuilds and it’s still useable now waiting for my next project. I agree it’s a bit expensive if only a few bits to do but for lengthy use it’s been invaluable.