R80RT fork oil question

[astroturf52]

Does anyone know the correct fork oil capacity for a 1986 R80RT?

My Clymer manual lists a capacity for all (I guess it means all since there is no year listed) R80RTs at 310-330cc. I just installed a new set of Progressive Suspension fork springs and of course had to change the fluid at the same time. I took the forks off the bike. I kept the forks together with the fork brace and front fender etc and simply turned them upside down into a drain pan to drain the old oil. I then added 320cc of fresh 7 wt. oil. The instructions that came with the Progressive Suspension fork springs said to put in the recommended amount of oil but in no case should there be more than 5.5" down from the top with the forks collapsed and the springs out. I've done this many times in the past with other bikes so I knew what that meant and believe I did it correctly. I have the special tool to get the level correct and I used it to remove the excess oil. In order to get the level to 5.5" down from the top I had to remove 80cc from each side. That left only 240cc in each side.?

I put it all back together and went on a 4 day ride with the new springs and oil. The fork really doesn't have much damping at all. If I sit on it and hold the front brake and ram it up and down it travels almost completely free of damping. The answer is that I have either too little oil or too light of a weight of oil. I have used 7.5 weight in several BMWs in the past (I used to mix 5 & 10 together but this time I was able to buy 7 wt.) with great satisfaction so I'm inclined to think there is not enough oil in there. I can simply add some oil and try it or of course I could go through the whole process again and use a heavier weight oil but before doing either I thought I'd ask all of you for advice.

One other possibility I can think of is that I didn't get all the old oil out by turning the forks upside down. I let them drain for a good long time but maybe you have to actually remove the drain plugs in the bottom of the fork legs to get all the oil out??? Even if that were true the old oil left in there would just add to the total amount and my 240cc number would be wrong. The level is still set at 5.5" down from the top. If there were some dirty oil mixed with the new oil it should still damp just fine.

Thanks for any help;

Turf

[Boxerkuh]

It sounds you did everything okay. I would drain the oil again and see how much you pull out. Then refill with 300 cc of oil. Go for a ride and if it is too soft, add 10 cc in each leg. I put anywhere from 300 to 320 cc of oil in, depending on the weight I use and the changes that I want to make to the ride. The more oil you use the stiffer the ride... but you know that... I am combining 5 and 10 wt oils and like the best at around 7.5 and 300 cc in each leg, but that is my preference... good luck...:eat :drink

[EastKy]

Hello, i changed my fork oil the other day to put new seals in. Now when I let go of the handle bars the front end goes into a tank slapping motion. I have a '86 R80RT. What could be the problem?

[ducatipaso]

your oil volume sounds right. i 2nd the drain and refill to double check.

re: tankslapping, this is usually caused by steering head bearing adjustment or front tire pressure.

[47512]

Fork oil capacity, generaly means with a dry fork, some forks have a damper tube inside the fork, like BMW forks, you can't get all the oil out by turning them upside down, some oil will remain in the damper unless you pump it out. As much as 25to50cc of oil can remain. So a refill can mean a over fill. Measuring the oil level is the correct way to do it. I have seen oil levels increased to overcome saging fork springs, with little or no air space you get hydrolic lock on compression whitch can damage fork seals. The springs will take up some volume when you reinstall them so don't get carried away with high oil levels, stay around 5" to 6" from the top of the tube. If you need more damping use higher vis oil, 10w works well in older BMW forks.

Ken G.