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Discussion Starter #1
Hello,

I have just disassembled my fork legs because of one leaking seal.
I was shocked when I saw the inner leg! There is a big horizontal groove with a 1mm difference in circumference on both ends.
The upper side of the groove is 47mm and the lower side is 48mm.
I've never seen a fork leg this worn and the bike only has 160 hours on it.
Have you guys ever seen it this bad? The entire upper leg is worn to 47mm which makes me think can a wrong type of oil cause this? lol
This is just from the leg that was leaking but I'm afraid the other leg will have the same mark.
Pretty sure I now need to get my hands on new inner legs..
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The bike is 12 years old. Did you buy it new? We do MX and take the bikes to around 300 hours before we sell them. The forks are always still almost perfect when we sell them. The lower fork leg (the "inner" one) is hard chromed and fork seals on a fork leg that has oil in it should not wear down the leg. Never seen any fork leg being worn down like yours!
 

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Discussion Starter #3 (Edited)
The bike is 12 years old. Did you buy it new? We do MX and take the bikes to around 300 hours before we sell them. The forks are always still almost perfect when we sell them. The lower fork leg (the "inner" one) is hard chromed and fork seals on a fork leg that has oil in it should not wear down the leg. Never seen any fork leg being worn down like yours!
I haven't bought it new. I have no clue what could have caused this crazy wear.. maybe the steel snap ring in the seal hmm.
I will check the other leg in a minute.
 

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Discussion Starter #4
I haven't bought it new. I have no clue what could have caused this crazy wear.. maybe the steel snap ring in the seal hmm.
I will check the other leg in a minute.
Other leg, same story.
Worn to 47.1mm

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Discussion Starter #5
Since they both have the same wear and only one was leaking, I think the leaking was not necessarily caused by this nodge. I don't even think the fork bounces out this high. (It's a 300exc supermoto and I only ride it on the streets)

So I'm going to replace both seals and see from there. If they start leaking again I would have to change both inner legs.
 

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So whatever caused it was going on on both legs! Wrong quality seals, some sort of harder material in them? And with you not being the first owner there is always a chance there is more hours than you know on the bike. But even then, that should not happen!

@augiedoggie, @DW, @cors187, have you ever come across this?
 

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Discussion Starter #7 (Edited)
So whatever caused it was going on on both legs! Wrong quality seals, some sort of harder material in them? And with you not being the first owner there is always a chance there is more hours than you know on the bike. But even then, that should not happen!

@augiedoggie, @DW, @cors187, have you ever come across this?
I will definetly pay close attention to the seals that are currently in and see if I can find something odd in them. I've already ordered new ones from 'All Balls'.

It's also very odd because the worn part of the leg is the part where the seal doesn't even go, it's the higher part of the inner leg and as far as I know the seal 99% of the time is about 4 inches lower than the start of the worn part. I'll add a picture of the fork where the inner leg is pulled all the way out. (the fork here is taken apart and the oil has been drained) I've drawn a marker where the worn part is.
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It seems to be undercut deliberately. Not sure if this is standard or why. It looks like a factory machine operation. Best to refer to factory manual to be certain. My advice in any event is to be sure to replace all bushings in fork or your seals will soon leak. Most quality suspension shop will not replace fork seals without fork rebuild for this reason. Worn bushings are commonly the reason for leaky fork seals. Replacing seals only can cause recurring leakage. Be sure to clean fork internals and replace all bushings for proper repair.
 

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Dirt Wizard
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For a second I thought we were talking about the inner tube, but looking at the pictures that's the lower tube. That's normal. They have to taper in as the outer tubes taper in at the top where they go through the triple tree.
 
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Discussion Starter #11
For a second I thought we were talking about the inner tube, but looking at the pictures that's the lower tube. That's normal. They have to taper in as the outer tubes taper in at the top where they go through the triple tree.
Great to hear that, thank you all for the help!
 

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Actually I might of fed you a bit of bullsh-t. Pretty sure the later 4cs outer tubes taper but the lower/inner one doesn't. I don't do so much suspension anymore.
I also looked up my white power manual and they do call that an inner tube. I always called the cartridge the inner tube. So my apologies there.
95% sure a few of them did taper in like that. The only thing that could wear that area would be that top bush if it come out of the groove, but I would suspect a very ugly wear and not smooth like that. You would have 2 sharp grooves where the split in the bush would rub on the tube.
 

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Discussion Starter #13
Actually I might of fed you a bit of bullsh-t. Pretty sure the later 4cs outer tubes taper but the lower/inner one doesn't. I don't do so much suspension anymore.
I also looked up my white power manual and they do call that an inner tube. I always called the cartridge the inner tube. So my apologies there.
95% sure a few of them did taper in like that. The only thing that could wear that area would be that top bush if it come out of the groove, but I would suspect a very ugly wear and not smooth like that. You would have 2 sharp grooves where the split in the bush would rub on the tube.
Hmm there's no further wear than just this smoothed area on both these legs. But I agree it's way to smooth.
I assume this must be one of the legs that were tapered then..
 

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I suspect the area in question is not chrome plated and the plating makes the large diameter standard size for slider. Probably no engagement point for slider bushing so no reason to chrome it. Your seal and bushing require hard chrome sliding surface. That part of slider is only going along for the ride.
 
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Thanks for your input gentlemen! As I have never seen this on any sort of forks I had no idea what was going on. Would be interesting (and assuring) to hear the thinking behind this from someone who was there when this became the norm (for whatever time it was) as in my 12 years of servicing and repairing our 2 stroke KTM's I have never come across this. Where could we find out more re this?
 

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Discussion Starter #16
I suspect the area in question is not chrome plated and the plating makes the large diameter standard size for slider. Probably no engagement point for slider bushing so no reason to chrome it. Your seal and bushing require hard chrome sliding surface. That part of slider is only going along for the ride.
Thanks for your input gentlemen! As I have never seen this on any sort of forks I had no idea what was going on. Would be interesting (and assuring) to hear the thinking behind this from someone who was there when this became the norm (for whatever time it was) as in my 12 years of servicing and repairing our 2 stroke KTM's I have never come across this. Where could we find out more re this?
This seems to be the case for the WP open chamber forks. I've watched a couple of videos and noticed the same taper on the legs. They just don't mention it it seems.
 

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That's why we post these things. Share our findings.
Very good for other people and us to learn.
I have definitely repaired a couple with the tapered tube before, but can't remember for what. I was back peddling when I mentioned that they're tapered because the outer tubes are tapered at the top as that was only an assumption.
Had a look at my huskies this morning and mine have a significant difference in diameter from the lower triple clamp to the upper. So I suspect mine will probably have a tapered inner or stepped inner.
 
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