Fork oil for 79 850 G

[Shakey]

I need to know how many CC's of fork oil to put into my 1979 GS 850G, I bought 10 weight and put in 260CC's but it isn't right. I bought some 15 weight and just need to verify the cc amount, if it is still too soft I will cut some shims and stifen the springs up a bit.
Thanks,
-Shakey

[rapidray]

MORE important than how much you put in is having a HEIGHT gauge to set it EVENLY at the CORRECT height in both forks. The amount you put in is only a guide to get you in the neighborhood. The height level after is what matters. Ray.

[BassCliff]

Hi Mr. Shakey,

The manual says 251 ml (milli-liters), that's about 8.48 US ounces. But, like Ray said, the fork oil height is very important. That should be 140 mm, measuring from the top, with the fork fully compressed. Look on pages 2-7 and 2-8 of the manual you downloaded from my website.

If you have an old pump spray bottle, cut the feed tube to the right length, stick it in the fork, and pump out the extra fluid.


Thank you for your indulgence,

BassCliff

[bwringer]

Hi Mr. Shakey,

The manual says 251 ml (milli-liters), that's about 8.48 US ounces. But, like Ray said, the fork oil height is very important. That should be 140 mm, measuring from the top, with the fork fully compressed. Look on pages 2-7 and 2-8 of the manual you downloaded from my website.

If you have an old pump spray bottle, cut the feed tube to the right length, stick it in the fork, and pump out the extra fluid.


Thank you for your indulgence,

BassCliff

And make sure the fork springs are out, too.

[Steve]

You said in your first post that "it's still too soft". Are you speaking of spring stiffness or damping strength?

Softness has a lot to do with spring strength, and it will show up when the bike sags a lot when your weight it put on it. It is often recommended that you not have more than 20-25% "sag" in your suspension. That is, if your forks have the typical 6 inches or so of suspension travel, that you use up no more than 1 to 1 1/2 inches just by sitting on it. This is where you want to adjust your spacer length on top of the fork springs. Even with new Progresssive springs, you will need to adjust your preload with spacers to get the correct ride height.

Switching to 15 weight fork oil will slow down your response to bumps. Assuming your springs are set correctly, a thicker fork oil will sharpen the blows from bumps because it resists movement more than 10 weight oil. If you have 'enhanced gravitational attraction' or are rather enthusiastic in corners (can bwringer keep up with you?), you might want 15 weight oil. For me, I like the comfort of 10 weight. My wrists were hurting from the constant jolts going down the road because the forks were not responding to the small bumps, but simply passing them on to my body. Simply switching to 10 weight oil cured that.

.

[Shakey]

I thought I wrote if it is still too soft...the 15 weight did stiffen it up some I will ride it in the morning for a real test. If it still does not feel right then I was going to shim it up a bit to preload the springs some. The bike sags around 1 to 1 and 1/2 inches when I sit on it.

[Steve]

I thought I wrote if it is still too soft...

Yep, you sure did, and I missed that one little word.

Just wanted to make sure you were not confusing soft springs (which affect ride height) with soft response (caused by too light fork oil).

Sounds like you are on the right track.

.

[Suzuki_Don]

Would someone like to give us less knowledgeable GS maintainers a rundown procedure on not a fork rebuild, but just draining and changing the oil. From comments I have read on site here we are being told to have the oil to a certain level with the forks collapsed with the fork springs removed. Would someone like to tell us (ME) how this is done in practice. Do the fork legs need to be removed from the frame to do this or is there some way to do it without a complete front end disassembly. I imagine dragging the springs out with the forks in place will get oil over everything.

Thanks.

[rustybronco]

Would someone like to give us less knowledgeable GS maintainers a rundown procedure on not a fork rebuild, but just draining and changing the oil. From comments I have read on site here we are being told to have the oil to a certain level with the forks collapsed with the fork springs removed. Would someone like to tell us (ME) how this is done in practice. Do the fork legs need to be removed from the frame to do this or is there some way to do it without a complete front end disassembly. I imagine dragging the springs out with the forks in place will get oil over everything.

Thanks.

If you choose to just drain and refill ...

support the bike so the wheel is fully off the ground, let the air out of the forks (if you use air) by depressing the pin on the "fill" valve located under the small caps, then remove the large threaded top fork caps pressing down as you un-screw it (be careful not to let it fly up at you).
just keep in mind, it has a rather big spring under it! (there is no need to remove the spring).
remove the lower drain screws on the outer sliders (tubes) and let them drain for a few hours into a drain pan.
put the screws back in, add the proper amount of your chosen fork oil, replace the top fork caps and add the proper pressure of air back into the forks if used.

I prefer to completely remove the forks, dis-assemble and clean them.

[Houdini]

Switching to 15 weight fork oil will slow down your response to bumps. Assuming your springs are set correctly, a thicker fork oil will sharpen the blows from bumps because it resists movement more than 10 weight oil. My wrists were hurting from the constant jolts going down the road because the forks were not responding to the small bumps, but simply passing them on to my body. Simply switching to 10 weight oil cured that.

So there is compression & rebound damping. I have always heard that the oil viscosity in these old forks "only" influences the rebound damping. From your post it sounds like the compression damping is affected...

I also feel a little harshness on big expansion joints; I was thinking of switching from 10 to 15 weight oil...thinking that the wheel was rebounding to fast...but now I'm not sure?

[Suzuki_Don]

Thanks Rusty. From your post I gather that if you don't remove the spring then you just add the amount of oil it says in the workshop manual after you have drained the old oil. If you are doing the measuring thingo then the springs have to be removed. Is that correct. If I removed the forks to do this job as you say that you do and give them a clean out while you are at it. What do you wash them out with after the old oil has been removed form each fork leg. It is assumed the forks are not being pulled apart to do this as the seals, etc. are OK.

[psyguy]

Would someone like to give us less knowledgeable GS maintainers a rundown procedure on not a fork rebuild, but just draining and changing the oil.

without taking the forks off the bike i would be weary of the following:
- the old oil draining down the lower forks and onto the discs (not good...)
- to remove the fork caps you need to remove the handlebars (and you want to remove the springs too - to wipe them off and to get a proper oil level measurement - the tolerance for the oil level is only +/-1mm!
- using this method it is difficult to get all the old oil out through "pumping" the forks

so, all in all, i prefer to remove the forks altogether

[Suzuki_Don]

without taking the forks off the bike i would be weary of the following:
- the old oil draining down the lower forks and onto the discs (not good...)
- to remove the fork caps you need to remove the handlebars (and you want to remove the springs too - to wipe them off and to get a proper oil level measurement - the tolerance for the oil level is only +/-1mm!
- using this method it is difficult to get all the old oil out through "pumping" the forks

so, all in all, i prefer to remove the forks altogether

Thanks PSYGUY. What do you wash the forks out with to get any sludge and old oil out before filling with new oil.

[Footy.]

In the haynes manual for my 78 GS750E, it says to renew the fork oil nine monthly or every 6000 miles.

Now it seems to me that with modern fork oils, the service interval should be way longer than this?

We don't throw our sealed rear suspention units away every 6000 miles do we!

What do people think?

Footy.

[psyguy]

Thanks PSYGUY. What do you wash the forks out with to get any sludge and old oil out before filling with new oil.

the fork oil is quite thin so most of it gets out easily

after draining the old oil out you can pour some new oil in, pump the forks a few times, and drain again

a step further would be to use some petrol first, drain, then the new oil, then drain again

if the inside is really dirty with sludge, you can use an engine oil detergent (such as you put into the engine oil before draining it out), but if it's THAT dirty i would want to have the forks appart for the cleaning (not just change the oil)