Changing fork oil do I have to put new fork seals?

My seals don’t leak but it is time for some fresh oil. Does it hurt the old seals when you pull the forks apart?

You can damage the seals if you aren't just a little careful, yes.

What you want to avoid is extending the fork farther than it does when it's assembled. There are some sharp, square cut edges for the seals to run over if extended to far. Try to avoid going beyond 8~10 inches and you'll be safe.

you don't need to pull the inner and outer apart to change the fluid. At least not that I'm aware - pulling them apart is only required when changing the bushings and seals.

Also - when you pull them apart, the seal does not drop into the square cut edge portion until you remove the bushing that sits there and then go to remove the seal.

The bushing IS the square cut edge I was referring to. The damper cartridge in either the twin chamber or open bath design is what limits the fork extension. Once this is disconnected, the fork can become hyper-extended, and seal damage can result.

You are correct in that it is not necessary to separate the upper and lower main tubes to change oil, though.

Could you explain a little further how to change the oil without taking the tubes apart I have a 08 450. Thanks for your help.

There are two oil volumes in the '05 and later fork, the inner cartridge, where all the damping is done, and the outer chamber. Assuming you have a manual, remove the cartridge from the fork as on page 5-18, but do not do any of the procedure for "Removing the inner tube" that starts on that page. Skip ahead to "removing the base valve" and follow that all the way to step 14 on 5-20. When you get to step 15, which has you replace the seals you didn't remove, skip ahead to step 24 on 5-21 and proceed.

There are two very confusing parts of the manual on the fork assembly. One deals with measuring a gap between the lock nut and rebound adjuster. The other "explains" the process of bleeding the cartridge. Read these two links for clarification:

http://www.thumpertalk.com/forum/showthread.php?p=8002008#post8002008

http://www.thumpertalk.com/forum/showthread.php?p=4985404#post4985404

Note that some of the page references in tese links may vary from your manual. They are from the '06 or '07 manuals. If you have trouble with that, download an '06 manual for the purpose of reading through:

http://www.yamaha-motor-europe.com/community/service/manuals.jsp

Pulling my forks apart, the inner tube has a square edge bushing - but on separation, it hits the outer tube bushing, the outer tube has a rounded outside edge bushing (both edges), however - that doesn't even matter since this bushing pushes on the flat faced washer which in turn pushes on the flat portion of the seal NOT on the inner ring edge surface that does the sealing. If I go to separate the upper/lower leg - none of these items will do any damage to the seal's inner surface -

Just sayin' - I don't get how separating the fork legs properly can damage a seal - there is nothing there that can do any damage......it can really only get damaged when you go to remove the seal from the inner leg and don't properly protect the square edge left once you remove the bushing that sits in it...

Then there is no reason for Yamaha to caution you against it. I'm glad to be relieved of that concern.

If you extend the fork beyond its normal limits, a row of holes below the upper bushing (on the inner tube) may be exposed to the seal lip, and may damage it. It doesn't always happen, and if you don't want to worry about it, don't. I don't frankly care. But it costs one very very little to observe the simple caution to avoid extending the fork completely if trying to salvage the seals.

Typically, the lower bushing (outer) protects the seal from touching those holes while the tubes are being separated - meaning the holes remain covered by the outer bushing during the pull apart process and only risks exposure once you remove the bushing from the lower fork tube.

I really don't care either since every time I separate a set of forks they automatically get new seals and dust wipers - it really only makes sense to replace them since they can have minor wear (invisible to us) from particulate picked up during it's life that could lead to seal failure in the near future, and depending on condition of bushings - new ones of those get installed as well.

I've read the warning before, but never understood exactly why they put it in if your parts are all installed correctly...

On the point of changing seals as a matter of course, I agree. No more often than it's necessary to change the oil, I just put new ones in.

But, the question was asked.

Then there is no reason for Yamaha to caution you against it. I'm glad to be relieved of that concern.

If you extend the fork beyond its normal limits, a row of holes below the upper bushing (on the inner tube) may be exposed to the seal lip, and may damage it. It doesn't always happen, and if you don't want to worry about it, don't. I don't frankly care. But it costs one very very little to observe the simple caution to avoid extending the fork completely if trying to salvage the seals.

:doh::snore::lol:

Amen Grey and it cost very little to replace the seals with new .....

I see no reason not to change the forks seals during every oil service and I see no reason not to completely disassemble the forks to properly clean all the crap out that can settle in unlikely places .... any other way is half @$$ IMHO.

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