fork oil quantity

Colin

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what is the correct amount of oil and what capacity. for a 1977 R100rs. motorsport.
I've got so confused, different manuals give different measurements.
I replaced all the internals and new stantions about 800 miles ago. put 8 fl oz of sae 7.
but they seem to be sticky, If I put the front brake on and pump the forks up and down. they don't return to the top of the fork travel. if i pull up on the handlebars the forks extend about 3". I need to remove the bottom screw plug on the r/h fork leg as it has a drip of oil. although i replaced the copper washers, the big sealing washer and PTFE tape around the threads.
"
 
Factory advice is 250cc per leg. SAE7 will be 'stiffer' than the recommended SAE5 but that's a personal preference. 8Floz ia only 236cc. It makes a difference.

Factory at build was 280cc but they changed it to 250cc after a few years.

Can't help with your leak.
 
thanks for the info Tim. I think I will try SAE 5. I see Rock Oil do SAE 5. And they are just down the road from me. I will try 250cc. The R90 looks good.
 
Colin said:
I replaced all the internals and new stantions about 800 miles ago. put 8 fl oz of sae 7.
but they seem to be sticky, If I put the front brake on and pump the forks up and down. they don't return to the top of the fork travel. if i pull up on the handlebars the forks extend about 3".
Click to expand...



You may have what is called "trapped stresses"....

Did you bounce the forks up and down (compress them) when on the bike to release any trapped stresses before tightening all the various nuts and bolts that secure the front wheel and fork stanchions in the yolks ?

If not then loosen them all, and with the bike off the stand hold the front brake on and bounce the front end up and down a few times, then re-tighten everything.
 
Steptoe said:
You may have what is called "trapped stresses"....

Did you bounce the forks up and down (compress them) when on the bike to release any trapped stresses before tightening all the various nuts and bolts that secure the front wheel and fork stanchions in the yolks ?

If not then loosen them all, and with the bike off the stand hold the front brake on and bounce the front end up and down a few times, then re-tighten everything.
Click to expand...

Leave the bottom yoke bolts tight or this won’t work.
And tighten from bottom to top (well, that’s how I was told to do it years ago….but I could be wrong)

Try a dowry washer instead of the copper washer on the bottom.
 
Bubb said:
And tighten from bottom to top (well, that’s how I was told to do it years ago….but I could be wrong)
Click to expand...

I've always done it 'top-down', but I might be wrong, too! My theory is that the top yoke levels the forks, so do them up as tight as you can by hand (with the tool kit spanner). Then you can tighten the bottom yoke bolts to correct spec (assuming they were free-running and not gripping the stanchions already without tight bolts - if they are tight, wedge them a little to allow the tubes to settle to the right height judged by the top yoke). Then you tighten the top yoke nuts to the correct torque, ensuring you don't twist the front end in that process (but I've always set the forks against the steering stop and applied the torque then). If you have a modified top yoke then things are a little different.

I hope all that makes sense - reading it again I could understand why it might not...
 
Some folks like to set the tube level so the axle spins freely in both fork legs when the forks are on full extension.
Pretty hard to tighten the forks up properly with the flat top plate without twisting them out of alignment, saw someone doing it as a three man job with a long bit of angle iron bolted to the top plate and two guys holding it. Easier to buy a billet T.T.-----.
Old forks might have a bit of a set, or twist, and have worn themselves in suit, some folks like to mark the tubes before disassembly so they can be replaced somewhere close the the same position.
And give them a good pump before you tighten the axle clamps, my tire guy didn't last time and you can notice the difference!
 
You have stiction which 'can' also be caused by tight bushes, bent forks or cheap seals (use SKF).

More likely though as suggested, tighten bottom yoke, top yoke, axle nut and clamp on that side, bounce the forks hard and without putting the bike on side stand lean down and nip up the other fork clamp which should have found it's happy place :)
 
Gelandestrasse said:
I've always done it 'top-down', but I might be wrong, too! My theory is that the top yoke levels the forks, so do them up as tight as you can by hand (with the tool kit spanner). Then you can tighten the bottom yoke bolts to correct spec (assuming they were free-running and not gripping the stanchions already without tight bolts - if they are tight, wedge them a little to allow the tubes to settle to the right height judged by the top yoke). Then you tighten the top yoke nuts to the correct torque, ensuring you don't twist the front end in that process (but I've always set the forks against the steering stop and applied the torque then). If you have a modified top yoke then things are a little different.


I hope all that makes sense - reading it again I could understand why it might not...
Click to expand...

Tim
That all makes sense to me. I must be wrong with my bottom up advice…. Top down makes sense with the BMW flat plate top yoke setting the fork height.
Thanks

Bubb
 
OK. I did bounce the forks up and down about 15 times to release air/trapped stresses.
and I did bounce the front with axle nut loose and bottom yoke loose. and I did put spacer washers under the bolts of that fork brace under the front mudguard. so it fitted just nice. not under stress. But I think I will go through it all again with all the bolts loose.
but i am wondering now if it is stiction from the seals.
will have a go at the weekend and report back. cheers
 
Timolgra said:
No that will make things worse by causing the seal to swell, use rubber grease.
Click to expand...

Everyday is a school day. Do the seals absorb and swell instantly? I was thinking just for a bounce or 3 this may not happen. Does the WD40 stay there forever?

Maybe it might have been better to say 'use the SAE5/7 fork oil' to lubricate the seals.
 
Gelandestrasse said:
Everyday is a school day. Do the seals absorb and swell instantly? I was thinking just for a bounce or 3 this may not happen. Does the WD40 stay there forever?

Maybe it might have been better to say 'use the SAE5/7 fork oil' to lubricate the seals.
Click to expand...

WD40 is a degreaser :thumb
 
today i sprayed a bit of silicon spray lube around the seals. bounced the front up and down and it was better. so I think it is stiction around the seals. they came from motobins but can't remember what make. are SKF better? my seals are blue colour.
 
Ride it for a while and it should become smoother.

Put a thin smear of rubber grease just above the seal and bounce the forks wiping off any excess.

Yes SKF are the best fork seals for durability and less stiction. Green.
 
Timolgra said:
Ride it for a while and it should become smoother.

Put a thin smear of rubber grease just above the seal and bounce the forks wiping off any excess.

Yes SKF are the best fork seals for durability and less stiction. Green.
Click to expand...

Are SKF seals available from motoworks-bins - or sherlocks or do i need to go to my local bearing suppliers. I've only just been back out on the bike. had health problems
but back riding again. done 40 miles on it today and forks seem worse. so will take apart and change seals and check everything else internally.
 
Colin said:
If I put the front brake on and pump the forks up and down. they don't return to the top of the fork travel. if i pull up on the handlebars the forks extend about 3".
"
Click to expand...

That tells you nothing other than you have some free sag! Probably excessive, so either your spring rate or preload isn't right...but there's more to it than that. Google 'sag'

Stiction:

1. Put a cable tie on the fork.
2. Compress the fork and allow it to return naturally.......take a measurement to the cable tie.
3. Lift the fork and allow to settle naturally under its own weight..........take a measurement to the cable tie

4. What's the difference between the two measurements?

20mm 'may' be acceptable
40mm suggests excessive stiction
 
Nippy Normans supply Touratech, Wunderlich, Desert Fox and many other makes of accessories.
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