Dr Big

Full Version: Fork oil change.
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Hi all, since fiddling with the rear suspension on my DRnotsoBig to make it softer, I decided to replace the #10 fork oil with #7.5.
As I have a DR600 headlight assembly attached to the forks, it would be a pain to remove and refit.. :tdown: ...even worse if I found #7.5 was too thin and needed to go back to #10.
So I removed the handlebars, the fork top caps, spacers and springs, compressed the forks, and used a length of 8mm steel tube attached to an old 12v SU fuel pump and pumped out the old oil into a measuring jug....replacing it with the same amount.
Its a pity they didn't fit drain plugs.... Banghead
I need a test run now to see if it's okay or if I need to go back to #10, or try a #5.
Dave...the eternal fiddler... Thumbup
Been thinking about this topic....
I may need to change the fork oil quite a bit with the widgets I'm planning on using and have been considering drain plugs. Also, as you say, t'would be nice to have em Thumbup
As I see it there's two options. Drill the 6 o'clock position of the bottom of the fork and tap a thread (m4?). This section of casting seems thick enough but would have to measure it to be sure I could still countersink the head and still have enough thread. Without having the bolt head flush it would foul paddock stands etc.

Other option is drill the centre of the large retaining allen at the bottom of the fork, tap it and use that as a drain plug, kinda like a threaded brake banjo with the internal bolt countersunk to allow you use the original bolt. Pro is super trick and tidy without a need for any disassembly and everything bar a bolt is still stock, con is it would leave about 15mm of fork oil at the bottom of the fork which isn't the end of the world if you change it immediately after a spin. What yas reckon, hairbrained or worth doing?
I like the idea of drilling the damper rod bolt at the bottom of the fork.

You really wouldn’t have to go to the trouble of designing it so the bolt could still be used since you’d want the oil out if you were pulling the forks apart anyway.

The other advantage is that if it doesn’t work out, you can just replace the Allen bolts with standard bits and be back to normal. I’d strongly recommend drilling the bolts on a lathe if possible. It would be difficult to keep centered on a drill press and likely impossible by hand.

For Dave.......you really don’t have too measure the volume of oil that comes out of the fork. The important measurement here is the “air gap” or measurement taken from the top of the oil level to the top of the tube with the springs out and forks compressed fully. Once your are happy with that measurement, you can just repeat it easily even with the forks on the bike just by accounting for the angle and repeating the measurement from the center, front or rear of the tube, whatever you want to use as a standard.
.....you really don’t have too measure the volume of oil that comes out of the fork.....

The reason I did that was to determine the amount of oil left in the fork, as I'm using stock springs but with 10mm removed from the cap to spring tubes... Thumbup