What the fork is wrong with my seals?

[bosco659]

This past winter I decided to replace my fork seals because the right fork had some evidence of seepage. I replaced both seals and refilled with 10W oil at the slightly higher than stock amount (as I’d read in other posts). After reassembly I noticed the forks seemed to be stiffer, meaning they were harder to get moving than before the rebuild. I thought this might be due to the new oil; colder temps; new seals and larger volume of oil.

My first ride of the season last week proved almost all my winter repairs were successful but the front forks just didn’t seem right. If I stopped at a light, applied the front brake and tried to bounce the front end, sometimes it would bounce “normally” and other times it felt like it was sticking, but once I applied more force it seemed to break free and bounce again.

I went for another ride this evening and much tge same was experienced. When I got back home I looked at the forks and the right fork was leaking pretty badly. Tells me I need to replace that seal again but why did it blow? On the left side was a different story. There were rings of a sticky black substance all over the tube and more around tge height where the forks would be near fully compressed. I tried to rub it off with my finer then a cloth and sit would wipe clean. I needed to use alcohol to clean the tube. I then deduced that this is what was causing the forks to be sticking in certain positions.

I will replace both seals again but want to figure out where that black sticky junk is coming from. Could it be a bad seal? I’d hate to re/re seals and have the same thing happen. I think when I do the seals I might use 5W oil instead of the 10W and use the factory recommended amount.

The bike is a ‘76 with 34mm forks. I have progressive springs (I think from XS650DIRECT).

Questions I have:
1. Is there a better quality seal available vs Mikes or XS650DIRECT?
2. Theories on the black deposits on the tubes?
3. Is going to 5W a bad idea?

First two pics are the black deposits on the left tube and the other two are the right tube with the leak.

Thanks.

 

[Jim]

If I had to guess, the black rings look like rubber breakdown from incompatibility between the oil and the seals.

All Balls has fork seal kits. Put 'em in the SG 6 or 7 yrs ago... still going strong.

 

[bosco659]

If I had to guess, the black rings look like rubber breakdown from incompatibility between the oil and the seals.

All Balls has fork seal kits. Put 'em in the SG 6 or 7 yrs ago... still going strong.

Thx Jim. I’ll see if they’re available for my ‘76. I’ve had pretty good luck with their stuff. Odd only one side is doing this but maybe the other is leaking badly enough that the deposits don’t stick to the tube. I got the seals from the guy I bought the bike from. They were from XS650DIRECT. The oil I bought was BelRay.

 

[Jim]

https://www.allballsracing.com/55-133.html

 

[bosco659]

https://www.allballsracing.com/55-133.html

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I need to buy more oil anyway. Is 5W too thin?

 

[5twins]

For those old forks, I would say yes. I think even 10w may be a little light. Don't they call for 30wt. motor oil? Lots of older bikes specced motor oil, I think simply because dedicated fork oil wasn't that common or easily found back then.

Make sure you clean out the lowers really good. Best way is to "swab" them out with rags dipped in solvent .....

 

[Jim]

I need to buy more oil anyway. Is 5W too thin?

Maybe. How's your rebound dampening?
I'm running 5W, but I only weigh about 140-150 or so, soaking wet. It's about right for me. If you're heavier, you might need thicker oil.
In any case, the weight "shouldn't" affect the seals.

 

[Its been a long time]

When I did the fork seals on my 650D earlier in the year, I used Yamaha fork seals. They were no more expensive than decent aftermarket seals. They are ARS brand as seen on many Yamaha seals. Given the amount of work involved in changing fork seals, I always use OEM seals if they're available.

I also use 5w fork oil, but I have a long standing preference for lighter rather than heavier fork oil.

 

[bosco659]

For those old forks, I would say yes. I think even 10w may be a little light. Don't they call for 30wt. motor oil? Lots of older bikes specced motor oil, I think simply because dedicated fork oil wasn't that common or easily found back then.

Make sure you clean out the lowers really good. Best way is to "swab" them out with rags dipped in solvent .....

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Yes I did clean the lowers out well when I did the rebuild (I recalled you mentioning this before in another post) - thanks.

I’ll get the new seals in and mess around with some different oil viscosities.

I’m still puzzled about the black marks although I agree with Jim’s probable cause. I do remember after I put the new seals in, even with springs out, it was difficult to collapse the forks. They were kind of stuck in the fully extended position and needed some coaxing to get the assembly moving. Once they started to move they seem to travel freely. Something wasn’t right, perhaps crappy seals? I’m also disappointed in the leak of the right fork tube. The tube surface seems to be perfect with no scratches or pitting - the tubes were replaced with new, aftermarket units about 5 years ago (7400 km). I’ll do a good inspection when I redo the seals this time.

 

[bosco659]

Maybe. How's your rebound dampening?
I'm running 5W, but I only weigh about 140-150 or so, soaking wet. It's about right for me. If you're heavier, you might need thicker oil.
In any case, the weight "shouldn't" affect the seals.

I weigh about the same as you Jim, but in kg. . Not really but I do weigh quite a bit more. The damping wasn’t so bad before I did the rebuild over the winter. Now, with the new seals and 10W oil, the fork action isn’t very smooth at all (but I think much of this is caused by the black gunk on the left tube). I sent an email to my parts guy to see what seals are available locally.

 

[bosco659]

When I did the fork seals on my 650D earlier in the year, I used Yamaha fork seals. They were no more expensive than decent aftermarket seals. They are ARS brand as seen on many Yamaha seals. Given the amount of work involved in changing fork seals, I always use OEM seals if they're available.

I also use 5w fork oil, but I have a long standing preference for lighter rather than heavier fork oil.

I’ll check out the Yamaha seals. Trouble is I no longer have a local dealer .

Edit: I just looked on Partzilla and the seal was $42 usd! Yikes. If that’s truly the going rate, a pair of seals up here would be about $120 Cdn after tax. I may need to pursue more cost friendly options.

 

[Its been a long time]

I’ll check out the Yamaha seals. Trouble is I no longer have a local dealer .

Edit: I just looked on Partzilla and the seal was $42 usd! Yikes. If that’s truly the going rate, a pair of seals up here would be about $120 Cdn after tax. I may need to pursue more cost friendly options.

It seems I misdirected you, apologies. The Yamaha seals for my 1977, 35mm are $11.

I have had good experience with NOK branded fork seals. They're original equipment in many forks and are definitely a step up from no name generic seals. Hope that helps, I'm sure you'll find NOK seals in a suitable 34mm size.

 

[bosco659]

It seems I misdirected you, apologies. The Yamaha seals for my 1977, 35mm are $11.

I have had good experience with NOK branded fork seals. They're original equipment in many forks and are definitely a step up from no name generic seals. Hope that helps, I'm sure you'll find NOK seals in a suitable 34mm size.

No problem, thanks for your comments. Over and above seal dimensions there’s too many seal types to chose from so I think taking the safe route of ordering them from a knowledgeable source will be best for me. Hopefully I can get the All's Balls seals as Jim suggested. They appear to be available on line so hopefully my dealer can get them.

 

[bosco659]

A friend suggested I try to work some fork oil into the seal that’s leaving the skid marks on the tube. I wiped the tube down with alcohol and applied a coating of oil on the surface. I bounced it dozens of times and so far there’s no black marks. Is there a way of getting oil under the seal to see if this is a possible cure?

When researching this problem last night I saw some vids that talked about this. They referred to it as “stiction” where the seal wants to grab onto the fork tube. Their solution was to get some grease under the seal lip. Perhaps when I assembled the seals I didn’t lube them sufficiently?

 

[bosco659]

Well with limited testing done I think working lube into the seal has eliminated the skid marks. A friend suggested a feeler gauge to create space to introduce oil to the seal.

The new seals will be here by the end of the week and I ordered 15W oil to check out the difference in damping. I still have enough 10W to fill the forks again if the 15W is too heavy.

 

[bosco659]

Just completed the @gggGary bent fork test and all looked ok. Draining the fork tubes right now. Looks like close to 175ml of oil. This amount was added using measurement from the top of the tube method. Maybe that blew out the seal? To be safe, when I reassemble them I think I’ll use the factory spec qty.

 

[bosco659]

Second mystery solved. Looks like I must have damaged the seal when I installed it. I do remember that side being very difficult to assemble and I had to beat the heck out of it to seat the seal. Looks like I beat it too hard and distorted it. The bore of the lower fork tube is rough from the po. so I’ll have to clean and polish it up before the next seal goes in.

 

[gggGary]

I've been coating my just out of the package seals with Tungsten Disulfide (WS2) it turns the rubber silver then pack the recess between the lips with lithium grease. I've been doing really good with this drill. No leaks, smooth action. A quick wipe of the OD with some grease helps when driving them in also.
For what it's worth the 76 seals I just put in came out and new ones went back in hard.

 

[bosco659]

I've been coating my just out of the package seals with Tungsten Disulfide (WS2) it turns the rubber silver then pack the recess between the lips with lithium grease. I've been doing really good with this drill. No leaks, smooth action. A quick wipe of the OD with some grease helps when driving them in also.
For what it's worth the 76 seals I just put in came out and new ones went back in hard.

Thx. I have a good qty of Tungsten Disulphide on hand and will use it on the new seals. I’ll use some lithium grease too.

The inside of one of my fork tubes is marked up where a po must have used a large, dull axe to remove the seal. There’s several fairly deep gouges that I need to address before putting the new seals in. I’ve filled the gouges with JB Weld and will sand them smooth tomorrow. Can you recommend any sealer I might apply on the OD of the seal as additional insurance against possible leaks? Maybe a very thin bead of Hylomar at the bottom corner of the seal recess, so once the seal is driven home, the bottom edge of the seal will contact the sealer?

That particular fork always used to have a ring of oil above the dust boot, but I could never see any oil where the tube met the seal. Maybe it was leaking from the outer perimeter of the seal and not the inner sealing surface

For seal installation, I do as most do and tap them on with a seal driver or appropriately sized socket. I was wondering if it would be preferable to push or press the seals into the fork tube. Perhaps a gentler, more controlled process. I think I have a monster sized c-clamp that may do the trick.

 

[gggGary]

Beat em in with a socket is what i do too. these 76 seals seemed unusually tight. hylomar my go to....