R80/7 Front Fork Alignment

[jackonz]

Can anyone give me a simple way of aligning the front forks on my R80, am using the original setup no modifications as far as I can tell, I have installed new seals and so on and new rings in the damper rods, and the correct amount of oil in the forks.
What I am experiencing is no sag when the bike comes off the centre stand, I read somewhere something about tightening the fork caps using anti torque but I have no idea what it refers to other then it is to stop the top of the leg being pulled to one side during tighting of the fork cap.

My only other option is fitting an aftermarket top tripple clamp as in the Toaster Tan item.

Thank you all.

[Kurt in S.A.]

This is one website...lots to read. About half way down, he has a picture of his anti-torque method.

https://bmwmotorcycletech.info/frontforks.htm

One way of doing things is to leave off the top caps of the legs and remove the springs. Then tighten the lower section starting at the top. I think if you put the axle through the lower legs, then each time you tighten something, push up on the axle...it should go smoothly. Keep working to the bottom. It's important to reduce the stiction at each stage.

Kurt

[gspd]

If you have no sag at all, the springs are too stiff or you have too thick of a spacer above (or below) the spring.
The spacer (if applicable) goes above the spring but I've seen bikes where a spacer was installed below it.

As far as alignment goes, use whichever method you choose among the many methods described by Duane Ausherman or Snobum, etc.
Bottom line: With the wheel and springs removed, If the axle slides freely and easily into position through both fork legs at full compression and at full extension, with the triple clamps and fork brace tightened, you're right on the money.

[Rob Frankham]

I am assuming that the suspension was OK before the bike was dismantled...

The first question is... when you say 'No sag' do you mean that the front of the bike doesn't settle when it comes off the stand or that the suspension can't be compressed by - say - applying the front brake and pressing down on the handlebars. If the suspension can be compressed and if it moves smoothly, then this isn't an alignment issue It could be a spring and spacer issue as described by GSPD or the other cause for "No sag" and by that I mean no sag at all, is that the forks are grossly overfilled with fork oil causing a hydraulic lock. My first approach would be to drain the fork oil completely and see if this changes.

If the forks won't move or are stiff even with the caps off and no fork oil, then yes you have an alignment issue and you have to start looking at the causes for this.

Fitting an aftermarket top yoke won't, of itself, fix the issue. You still have to get the alignment right.

Rob

[barryh]

I would separate the two possible causes i.e. spring stiffness or alignment, by removing the springs and then stroking the forks by hand to check for stiffness. Correct alignment issues if any, before moving on to the springs.

You mention new rings in the damper rods, there has been some talk of new replacements being over size and causing excessive stiction but you should be able to detect that by hand stroking with the springs out.

[jackonz]

OK, first off thank you all for your advise.
As far as I am aware the forks seem to be original and had never been apart, when I picked up the bike I road it home 4 miles and from there I started the re commission, the bump stops top and bottom had dissolved in to nothing and the seals were leaking and oil was also leaking from the bottom, the oil in the forks did not seem too bad so I am thinking that it had been replaced at some point and as it was red I am assuming it had ATF fluid in the legs.
As for what they were like before I honestly cant recall as my major concern at that time was stopping the bike as the brakes were awful.
The spacers that came out were at the bottom of the springs so they went back in that way.

Before fitting the springs I had everything fitted and I could move the legs freely up and down with the axle in place as I have done on many bikes have rebuilt in the past.

What I am getting is no sag when I take the bike off the centre stand, I can compress the forks when I push down with the brakes applied.

BMW NZ have genuine fork oil in stock a 1 Litre can of the stuff so I have placed an order for it, I also wonder if the spacer should be on top of the spring rather than the bottom as if it may be restricting the oil flow through the damper in to the area where the spring is.

Am in no rush to panic fix I want to get it done correctly but it seems BMW had so many different forks in this era it's hard finding the correct assembly drawing, mine seem to be the ATE legs with ATE brakes.

[jackonz]

All, I spent an hour or so yesterday looking through the files of paperwork that came with the bike and found a bill for a service on the bike, it was done about a year prior to me getting the bike and in it it says the fork oil replaced with ATF fluid.

Also in there was a quote here in Nelson NZ from the same shop to replace the fork seals, pushrod tubes, sump gasket and suspect rear main seal amongst a few other minor jobs that needed doing as well as looking in to a dragging clutch.

Seems to tick off all the work i have done so far, question is has anyone here used ATF in the forks and know the results?

[Kurt in S.A.]

Some info about fork oils, including some versions of ATF on Snowbum's page...some might be oldish but maybe worth comparison??

https://bmwmotorcycletech.info/front-fo ... mounts.htm

Kurt

[barryh]

ATF is in the ballpark for viscosity but for me a little on the thick side being closer to a typical 10W fork oil than a 5W which is what I use. Bear in mind that's a generic figure for ATF viscosity and if you knew what brand of ATF had been used it should be possible to find the viscosity from the manufacturers data sheet. ATF tends to be in the mid to high 30's cSt @ 40 deg C which is the temperature you should be looking at. I prefer approx. 20 cSt. The original BMW oil is only 13 cSt

[jackonz]

ATF is in the ballpark for viscosity but for me a little on the thick side being closer to a typical 10W fork oil than a 5W which is what I use. Bear in mind that's a generic figure for ATF viscosity and if you knew what brand of ATF had been used it should be possible to find the viscosity from the manufacturers data sheet. ATF tends to be in the mid to high 30's cSt @ 40 deg C which is the temperature you should be looking at. I prefer approx. 20 cSt. The original BMW oil is only 13 cSt

Hi Barry, thanks for the info, I will see what this OEM fluid for the forks is before I take the plunge but have looked up in relation to the info you supplied and Spectro have a fork oil that matches if I need to go that way.

Hope it's not too cold back there in the UK.