Forks still leaking a bit after rebuild

[rainman]

Hi folks, long time no see, hope life is treating you all well.

I rebuilt my USD forks on my VZ800 last weekend and followed the book closely. It's been a long while since I did a fork rebuild on any bike but it's not the most difficult job, and I was careful, so I thought anyway. Checked them out after the rebuild and they didn't leak, and kept an eye on them during the week too, while I rode my identical commute every day. They started off good, by Wednesday they were a little weepy (but very minor), and now they're a little more than that - not pissing oil all over the place, just not running clean. I'm wiping up after every trip and keeping the brakes clean but obviously need to fix this soon.

I'll redo the job and make sure I'm extra careful but is there anything obvious I might have done wrong, or some other problem that might be causing this? Damper rod forks, USDs as I mentioned. Seals seated well when I put them in, and the tubes had a little corrosion but just below the seals, and I cleaned that up as best I could. I didn't have the Suzuki special tools but they came out easy with a flattie, and I made a clean PVC tube of just the right size to seat them. Put in exactly 838ml, the right weight of fork oil, and checked the level after - spot on. I couldn't torque the lock nut on the top exactly but think I got it pretty close - if I cocked that up surely it would leak from the top? Didn't change the O-rings or the dust seals as they looked good, just gave them a clean and back in.

Any ideas?

[Ocean1]

Any bushes in there?

[rainman]

Do you mean the oil seal retainer that the seals sit on? (On the other side to the circlip).

[drift77nz]

Fork Bushes. Usually on USD's there is one on the top of your inner tube and one in bottom of your outer tube (behind the seal). If these are worn, the inner tube will move to much laterally and the seal will leak. Any pitting on your chrome inner tube can cut out your seal. What brand of fork seals did you use? Not all fork seals are created equal. Did you use a plastic bag over the inner tube when you fitted the seal over it?

[Ocean1]

Do you mean the oil seal retainer that the seals sit on? (On the other side to the circlip).

Fork Bushes. Usually on USD's there is one on the top of your inner tube and one in bottom of your outer tube (behind the seal). If these are worn, the inner tube will move to much laterally and the seal will leak. Any pitting on your chrome inner tube can cut out your seal. What brand of fork seals did you use? Not all fork seals are created equal. Did you use a plastic bag over the inner tube when you fitted the seal over it?

That's the one, particularly the bush right behind the seal.

Modern seals are very intolerant of high axial clearances, and the better quality seals no less so because they're designed to minimise "stiction", which means very thin seal lips and high seal body clearances.

I'm not familiar with the bike, but if it's done enough work that the seals were leaking then chances are you might have got away with replacing the bushes with new ones and putting the old seals back in again. Not that you would, but the leak is at least as likely to be caused by bush wear as seal wear.

Also, check the seal cavity, you wouldn't be the first to scratch the bore surface during removal and that's all it takes for the oil to track around the outside of the seal. A bare hint of sillycon deals with it.

[rainman]

Fork Bushes. Usually on USD's there is one on the top of your inner tube and one in bottom of your outer tube (behind the seal). If these are worn, the inner tube will move to much laterally and the seal will leak. Any pitting on your chrome inner tube can cut out your seal. What brand of fork seals did you use? Not all fork seals are created equal. Did you use a plastic bag over the inner tube when you fitted the seal over it?

Thanks - the thing behind the seal is called an oil seal retainer in the manual, and it's quite skinny. To me a bush is a fatter thing kinda like this:
http://www.thetuningworks.co.uk/stor...1152-08D00.jpg. My one looks like a washer and it was in good nick. Nothing at the top of the inner tube but a rubber seal and a lock washer. Could be I didn't get that tight enough and it's wobbled loose? Will have a look. I used All Balls seals as that's what I could get - and because I couldn't tell you if they're good or shit. There wasn't any pitting on the inner tube, it looked quite tidy actually for the fact that it's a 17 year old bike.

Didn't use a plastic bag as it's a tight fit as it is - where do you put the plastic bag?

That's the one, particularly the bush right behind the seal.

Modern seals are very intolerant of high axial clearances, and the better quality seals no less so because they're designed to minimise "stiction", which means very thin seal lips and high seal body clearances.

I'm not familiar with the bike, but if it's done enough work that the seals were leaking then chances are you might have got away with replacing the bushes with new ones and putting the old seals back in again. Not that you would, but the leak is at least as likely to be caused by bush wear as seal wear.

Also, check the seal cavity, you wouldn't be the first to scratch the bore surface during removal and that's all it takes for the oil to track around the outside of the seal. A bare hint of sillycon deals with it.

Thanks, will do. The cavity below the circlip ring (the bit between the seal and the dust cover) was a bit corroded and I'm wondering if that's where the problem is. When I redo them I'll get the magnifying glass out and check if it doesn't reach back under the seal slightly. I'm still a bit confused about the bushes as there is no record of separate bush parts in the manual, or online - just the oil seal retainer.

Maybe when I redo them I'll test to see if there's any lateral movement after I put them back together.

Thanks for the help.

[drift77nz]

[QUOTE=rainman;1130682532]Thanks - the thing behind the seal is called an oil seal retainer in the manual, and it's quite skinny. To me a bush is a fatter thing kinda like this:
http://www.thetuningworks.co.uk/stor...1152-08D00.jpg. My one looks like a washer and it was in good nick. Nothing at the top of the inner tube but a rubber seal and a lock washer. Could be I didn't get that tight enough and it's wobbled loose? Will have a look. I used All Balls seals as that's what I could get - and because I couldn't tell you if they're good or shit. There wasn't any pitting on the inner tube, it looked quite tidy actually for the fact that it's a 17 year old bike.

The washer behind the seal is usually what pushes the bush into the outer tube. Had a look at the parts catalog. Doesnt show the bush in the parts catalog so maybe it doesn't have a removable bush. If this is the case and it may be worn too much you may be up for a new tube.
I think your problem is more than likely to be the seals. I have used All Ball seals in the past and they are shit! Although mainly on mx bikes I have not had much success with them and hence do not use them anymore.


Didn't use a plastic bag as it's a tight fit as it is - where do you put the plastic bag?

Good practice when fitting seals in USD forks is to slide the seals on the inner tube first. You put he plastic bag over the end of the inner tube while you slide the seal over the end to eliminate damaging the seal surfaces. Then insert the inner into the outer and "drive" the seals into the outer tube with a fork seal driver. Since you have All Ball seals, and they are tight, you probably won't be able to do this. Throw them away and get some factory seals is probably your best option.

[Ocean1]

Thanks - the thing behind the seal is called an oil seal retainer in the manual, and it's quite skinny. To me a bush is a fatter thing kinda like this:
http://www.thetuningworks.co.uk/stor...1152-08D00.jpg. My one looks like a washer and it was in good nick. Nothing at the top of the inner tube but a rubber seal and a lock washer. Could be I didn't get that tight enough and it's wobbled loose? Will have a look. I used All Balls seals as that's what I could get - and because I couldn't tell you if they're good or shit. There wasn't any pitting on the inner tube, it looked quite tidy actually for the fact that it's a 17 year old bike.

Didn't use a plastic bag as it's a tight fit as it is - where do you put the plastic bag?



Thanks, will do. The cavity below the circlip ring (the bit between the seal and the dust cover) was a bit corroded and I'm wondering if that's where the problem is. When I redo them I'll get the magnifying glass out and check if it doesn't reach back under the seal slightly. I'm still a bit confused about the bushes as there is no record of separate bush parts in the manual, or online - just the oil seal retainer.

Maybe when I redo them I'll test to see if there's any lateral movement after I put them back together.

Thanks for the help.

Yep, that looks like a typical fork bush. It may not have them, most early Jap forks I worked on didn't. If that's the case you're up for new outer cases, although I did machine a pair once to take them.

If they leak a tad overnight, (as opposed to only when riding) then you should be able to see if the oil is coming from the seal/inner interface or from the seal/outer.

It's not difficult to damage the seals installing them. The press tube/tool should bear on the body of the seal, out to almost the full OD but clear of the seal lip at the ID and it needs to be square to the fork centreline throughout the operation.

[jamesfry]

How much it is leaking? It is perfectly normal for a fork to leak some oil/grease away from the stanchion seals after rebuild/service and it would probably be improper assembly if it did not leak at all. Although leaking should reduce after a while.

I would at least clean and inspect stanchions and seals after every ride. If leaking reduces significantly after about 10 rides it is probably normal.

[manxkiwi]

A piece of old 35mm negative has worked for me in the past. Make sure there are no sharp corners on the strip, where it may have been cut. Press it on to the fork leg to follow the shape. then very carefully slide it up under the seal. Then rotate round at least one full revolution. This can align the seal lip if it isn't sitting correctly and/or shift a bit of debris that could possibly be there?

Cheap and worth a go before re stripping your forks. I have done this on two sets of re built forks and it did the job for me.