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Fork Oil Filling Method

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WR450 2007. I am at the stage where I am putting in new fork oil after disassembling and reassembling my forks. I have never done this before but I have the correct oil, I have the correct measuring tool, I have read the manual and I have watched Dirt Bike, Dirt Rider, Rocky Mountain Youtube videos.

I just want to check what the correct way of pumping the damper and outer tube is before measuring the oil to dump all the air. The manual says to fill and pump the damper more than 10 times, then fill again and move the outer tube up and down but no more than 7.9 inches else air will get in, then measure.

Racetech instructions from what I can understand say to fully extended and then fully compress the outer tube before measuring the fork oil which seems the complete opposite from the manual.

In the Youtube videos I don't think they move the outer tube, only the inner damper.

I remember reading at suspension thread where someone was warning that if you get air stuck in a particular place it could blow the internal seals and completely mess everything up requiring another rebuild. Can someone shed some light on this as I can't remember where I saw this warning and what bit it was referring to. I don't quite understand the reason for moving the outer tube, where does the air get stuck around there?

Edited by Snow Drift

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2007 forks are Open Chamber forks, not Closed Cartridge forks, and do not have 'inner seals'.

It's just a spring base valve and a mid valve stack with a piston sealing ring.

Watch this video at 13:00 + for everything on how to correctly set up your kind of forks.

 

 

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Thank you that video was very helpful. I had watched the other video Dirt Rider made, presumably for closed chamber forks. Although I realised my forks weren't the same as in the video I assumed that there were differences between models so just followed the general idea of what he was doing.

 

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4 hours ago, Snow Drift said:

Thank you that video was very helpful. I had watched the other video Dirt Rider made, presumably for closed chamber forks. Although I realised my forks weren't the same as in the video I assumed that there were differences between models so just followed the general idea of what he was doing.

 

2003 to 2011 is open bath. 

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Snow

First fill the fork with oil, as per amount in manual

Then with fork fully compressed, you need to pump the inner damper rod to bleed out the air from the chamber. Ignore the manual with regard to stroke length, you can move the rod up and down the full stroke without any air getting back in. Keep doing this until you feel no more air in the chamber and the force required to move the rod is constant along its full length of travel. You will feel if you still have air trapped in the chamber by the differing force require to move the rod during its stroke

Next, you need to set the oil level. The Race tech instructions tell you pull the outer fork tube all the way up. This is to displace the oil trapped between the inner and outer tubes back in to the inner tube. If you don't do this you don't know how much oil is between the inner and outer tubes and it affects the oil height - this is their solution to getting consistent oil level heights.

Next, fully compress the fork and measure the oil height. I use a 6in steel rule and insert it the fork until the 150mm line is level with the top of the fork out tube. Withdraw the rule and see where the oil has come up to on the rule. If its at 40mm you have an oil height of 110mm (150-40). Adjust to your required height.

As explained in the RT instructions their recommend height is much higher (smaller mm value) than the Yam manual because you have no oil between the inner and outer chambers because you displaced it all into the inner chamber when you extended the forks in the second step above. I ran mine at around 90mm

 

The air getting trapped/stuck that you mention is to do with close chamber forks and as stated above you have open chamber so this does not happen on your fork

I take it you got the Gold valve kit installed then?

Edited by GuyGraham

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