Fork oil change

5 replies to this topic
  • luvmythumper

Posted February 22, 2001 - 11:17 AM


I have a 2001 426. It's time to change the fork oil. The manual only gives the comlete dissassembly/assembly instructions. How much disassembly do I need to do in order to change the oil? Any special tools needed just to do the oil change. Thanks in advance for the advice!!!

  • MikeOK

Posted February 22, 2001 - 02:08 PM


To do it right you need to completely disassemble the forks. But I don't do this every time. For a simple oil change you can just dump out the oil, move the works back and forth several times to get most of the oil out of the inside then fill as the manual shows. You need some way to measure the oil height and you can buy a special tool to do this, but I just use the squirter out of a spray bottle with some black tape at the measuring point. Some of these guys will have some better home-built ideas too...

  • DaveJ

Posted February 22, 2001 - 02:30 PM


My thoughts are that you should do a full disassembly since it's really not that much work. This will assure that any debris will be completely removed and allow for a complete inspection of bushings and polishing of tubes.

And I really don't recommend that you use solvent since this leaves a residue. The self-evaborating contact cleaners are fine, but they cool the metal and attract water vapor. Clean dust free towels and a good wipe down are best for most of this stuff.

Let me know if you need any additional help.

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  • luvmythumper

Posted February 22, 2001 - 04:55 PM


Thanks for the replies. I will try this weekend doing the full disassembly. What about special tools. The manual called several out. I will use Mike's idea to measure the oil height. Any other tips?

  • jj

Posted February 22, 2001 - 07:10 PM


Hey Mr. Luv! I did a search for some posts I made awile back on the subject. They may not make total sense cause they were addressing other posts but you'll get the idea.

"If you are refering to the Cap bolt on top of the fork its 19mm. If you are refering to the base valve at the bottom of the fork it is a 14mm hex/allen. You'll also need a thin 17mm wrench to get the cap off of the damper rod. I found that a thin 11/16 wrench works as well. Found mine at Sears. You'll also need a turkey baster and about a foot of plastic tubing that fits on the end of the turkey baster. As far as oil goes, the manual says use Yamaha 01. I've heard that Yamaha 01 is equivalent to 2.5 weight, 5 weight and 7 weight. Every dealership had a different opinion... I talked to alot of suspension shops, they also differed in their opinions but the majority agreed on 7 weight specifically, Spectro 125/150 (7 weight).
If you plan on pulling the fork completely apart let me know and I can help with some helpful hints. But, if you just plan on changing the fork oil follow these directions.
1. Before you take the forks out of the clamp loosen the Cap bolt (19mm). Loosen it just enough so that when you take the fork off you can still get it off while only holding the fork tube with your hand and just enough so that the oil doesn't leak out if you lay it down horizontally.
2. If you have access to an impact driver and a 14mm allen that it's definitely the best way to get the base valve off. Using the impact driver allows you not to have to buy a cartridge-holding tool to hold the cartridge from inside while you take off the valve. The driver actually spins the valve off fast enough so that you don’t have to hold the cartridge.
You can drain the forks without taking of the base valve but I wouldn't recommend it. It takes forever, you have to constantly pump the cartridge rod up and down over and over to get the oil out of the cartridge. Even then you can't be sure you got it all. Besides you'll find quite a bit of grit and grime just inside the base valve.
Whatever you do, wash the forks out and off with a contact cleaner you are sure doesn't harm plastic or rubber. I use PJ1 Super clean, good stuff.
After you've drained the oil and cleaned the fork out and off;
1. Follow the directions in the manual all the way up to the point where you first fill the tube with oil.
2. Fill the tube like the manual says, all the way to the top of the outer tube. You'll notice the cartridge rod will be just below the surface of the oil, no big deal, just grab it and pump the rod all the way up and down more than 10 times. You'll notice that while you are pumping the rod the oil level will drop alot, keep the oil level full as best you can, don’t let it drop to much.
3. After you pumped the rod and noticed the oil level isn't changing any more tap the tube lightly to get the air bubbles to the top. Let the fork sit for at least 10 minutes so that the bubbles have enough time to get to the surface.
4. After you're sure all the bubbles are out. Fill the tube again all the way to the top of the outer tube. Grab the outer tube and move it slowly upwards, go slow, and just like the manuals says dont raise it more than 7.9 inches. What you are doing here is filling that space between the inner and outer tube with oil. If you do raise the tube to high you may hear a sucking sound, if you do you've just sucked air into that space, BAD! Refill the tube and start over.
5. Now you are ready to measure your oil level. Fill the tube again, if you see more bubbles let it sit awhile more. I checked around quite a bit on what oil level was best and of course heard many different opinions. I did hear one level more than I heard others though, 105mm, I went with it. Make sure that your plastic tubing will fit down between the spring guide and the tube. Take the tube and make sure that the end you plan to stick in the oil is cut straight. Take that end and measure up 105mm. Put some tape on that mark. When you insert the tube into the fork, insert it all the way to that tape. That way when you suck out the oil to that point you'll be left with exactly 105mm. I found that I had to drain my baster once and re-insert the tube again during the process to get the level down to 105mm.
5. At this point you're done, follow the directions in the manual on putting everything back together.
6. One note when you put the push rod back into the damper rod you displace quite a bit of oil from inside the damper rod. When you are ready to put the push rod in leave the forks completely compressed so that the oil that is displaced will only flow back into the tube and not all over your fingers.
Hope this helps, if I can help further let me know.
1. Clean the whole fork thoroughly before you disassemble it.
2. Disassemble the whole fork, cartridge and all. This will allow you to drain ALL of the old oil.
3. If you don't want to buy a cartridge holding tool you can use an impact driver and a 14mm hex head socket.
4. Remember to first loosen the base valve before you take off the fork cap.
5. Find a 17mm or 5/8 "thin" wrench for use on the nut located under the cap bolt (see manual). A regular craftsman wrench is to thick.
6. Use a heavy plastic bag to help slide on the new seal (good pictures in the manual)
7. Motion Pro fork oil level tool is worth the $30
8. When you replace the base valve use lock tight
9. Before you slide the dust seal back into place stuff as much waterproof grease as you can up next to the seal and clip. This will help keep dirt and grime out of the seal. Oh, I used Silkolene RG2 (great stuff!)

JJ from WA - 99 WR; WR timed, EKN Needle, Scotts stabalizer, Scotts triple clamps, Pro-Tapers, Michelin S-12's, Terry Cable hot start, MSR Raptor clutch lever, Moose skid plate, Works frame guards, Acerbis Pro Rally guards, Renthal MD-soft grips, Factory Effex graphics, YZ IMS seat base, YZ Factory Effex seat foam and gripper seat cover, YZ rear fender

  • JBM

Posted February 23, 2001 - 07:48 AM


I have heard from a very good suspension guy, Jeremy Wilkey at, that Mobil 1 ATF is great to replace your fork oil with. I think he uses it all the time. It is in mine now. When I had mine replaced for the first time there was a noticable improvement in fork action, it was smoother through the stroke. Some of this is probably due to just changing the oil, but some has to be credited to the Mobil 1 as well.

[This message has been edited by JBM (edited 02-23-2001).]

[This message has been edited by JBM (edited 02-23-2001).]

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