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Finally getting back to this.

How much time should be allowed to drain the oil out of the fork? I have drained the Left Fork twice now, and each time when I refill it, it will only take about 160 ml to fill to the 75 mm level. This is about half what the manual says it should take. I feel like I am missing something in my understanding.

Am I missing something?
(I know, I am just repeating my earlier question and hoping for a new answer, but I am frustrated.)
 

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You’re doing this before replacing the spring?
Yes I was measuring the level with the spring removed.

I filled it to the prescribed level, and put it all back together. I am going to take a test ride before I start on the right fork.
 

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Finally getting back to this.

How much time should be allowed to drain the oil out of the fork? I have drained the Left Fork twice now, and each time when I refill it, it will only take about 160 ml to fill to the 75 mm level. This is about half what the manual says it should take. I feel like I am missing something in my understanding.

Am I missing something?
(I know, I am just repeating my earlier question and hoping for a new answer, but I am frustrated.)
While the fork leg is draining give it a pump up and down a few times to make sure you empty out the cartridge, found out my triumph forks hold a fair bit of oil in there.
 

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While the fork leg is draining give it a pump up and down a few times to make sure you empty out the cartridge, found out my triumph forks hold a fair bit of oil in there.
Did that.
 

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I know @Panzermann says otherwise, but I still can't help but wonder why BMW says to remove the damper unit completely to get all the oil out. I know they go to extremes sometimes, but that's their procedure for a fork oil change on ESA forks. I've not done this myself, just reading the repair and service DVD.
 

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Discussion Starter #68
The good oil ...

With the 60,000 km service due, it's time to change the fork oil again. When ordering some engine oil online some time ago, I threw in a litre bottle of Castrol 10W, knowing this service was approaching, but forgetting for the moment this time around I had decided to try the genuine article (gold standard BMW 11.5W) to see if I could detect any difference. I rued the wasted $17.21.

Today I fronted up to the spares counter for my genuine BMW supplies, trying to act nonchalant as I asked for an air filter, oil filter and a litre of 11.5W fork oil, whilst all the time apprehensive about the price of the latter. The oil was on back order from Germany, but the attendant offered to seek a bottle from the workshop. While waiting, she told me the prices of the air and oil filters: $45 and $35 respectively. The service manager, Josh, eventually arrived with the Holy Grail, willing to offer it on credit to the spares department on the undertaking they would hand deliver a bottle under armed guard when the back order came in. Josh is a nice bloke, but always looks serious despite underlying friendliness. "Changing the fork oil, are you," he enquired politely, knowing that his service department gets minimal business from me (maybe there was a hint of resentment in his voice …).

Funny that the quoted prices are such round numbers (especially as compared with the parts fiches available online - US$36.10 and US$19.57 respectively). I always try to dress down and look old when I go to the BMW parts counter, hoping for a hobo (or at least seniors) discount; sometimes it works ("I'll give you that for only $150" - and I feel pleased that I've got a bargain). I'm not sure if it worked this time because when the fork oil was produced, the stated price was $60 (compared with the fiche price of just $US23). I tried not to grimace, but I think it showed. No further hobo/senior discount was offered. I rode home feeling I'd done the best for my bike. After all, the fork oil works out at only 0.2 cents per kilometre, and my bike would love me for the extravagance.

Then I got to wondering about how much different the BMW oil was to the Castrol stuff, especially given I was happy with Castrol 10W for the last 30,000 km (much better than the original fill, presumably of the original spec 7.5W BMW oil). The oil viscosity label on the bottle means very little apparently, except, perhaps, in relation to the same manufacturer's other fork oils. So I was curious to find out.

The fork oil change will be done another day (it's a meticulous job, so I like to allow plenty of time) but I could do some comparisons in the meantime. First think to note is that the BMW product is a little more strongly coloured – a little more yellow/golden. I suspect this is due to the nano-particle gold additive that justifies its price. Viscosity-wise, I thought I'd do some experimentation, with on-road testing having to await another day.

To measure the relative viscosity of the two oils, I employed the syringe I use for rear drive oil, removing the plunger and filling to the 150 ml mark, then measuring the time taken to drain to the 10 ml mark. For each oil, I repeated this for five measurements at ambient temperature, with good repeatability (standard deviation less than 2% for all measurements).

Given ambient was only 14 deg C today, and fork oil heats with use (calibration testing is normally done at 40 deg C and 100 deg C, I understand) I decided to warm the oil by placing each bottle in a bath of hot water for some time to bring them up to about 40 deg C, and for each oil measuring the temperature at the beginning and end of each test and then taking the average. Given my test rig, was not ISO compliant I determined the units of measure would be centiPanzers (cPz) rather than centiStokes (cSt - who is this bloke Stokes, anyway?). I didn’t try to heat the oil to 100 deg C for more thorough testing – my plastic syringe wouldn’t have handled it and it would have been pretty risky handling boiling oil (in the kitchen …).

With so few data points, it is difficult to draw definitive conclusions, but I'm satisfied that the two oils are not far apart in their viscosity, so if you prefer to pay $0.0006 rather than $0.002 per kilometre for your fork oil, then go Castrol 10W and you won’t be far off the absolute optimum. Otherwise, man up and pay for the gold standard (try as I might, I could not discern those gold nanoparticles, so BMW's oil manufacturer has done a great job concealing them). I’ll change the oil in a few days – I wonder if I’ll be able to discern any difference in service …
 

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Good Oil

And Sturgeon thought the overfill experiment would be a waste of good oil.:laugh2:
PZ seems to love playing with oil.:grin2:
Cheaper Castrol for me, thanks. The BMW oil seems to be about the same.:iagree:
 

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Discussion Starter #72
Gold standard fork oil

The eagle eyed (and/or partially interested) among you would have noticed the obvious error in my fork oil viscosity analysis post earlier—I had transposed the axis labels (Excel used to be much easier until Microsoft improved it). This error occurred to me early one morning in bed. I don’t know why. I didn’t bother to share this revelation with my dear wife—she often wonders why I wonder about so many things, and I wasn’t going to give her more to wonder about that early in the morning.

A new version is shown below.

Last Saturday afternoon I spent a therapeutic few hours in the garage changing the fork oil rather than just wondering about it. In preparation, I went through the Haynes manual and typed up a dot point checklist, to avoid frequently losing my place in the newsprint text. This also helped reacquaint me with the process, so by the time I got into it, everything was much more familiar (it had been ~18 months since my first change and I’d lost the scribbled first version of my dot points).

Of note was that the drained oil looked new rather than discoloured as it had on the first change and consequently I didn’t bother to flush the forks with kerosene (paraffin). I wonder if any of the earlier discoloration was due to assembly grease rather than wear on the internals. My replacement rear drive was like that at the first change—blackened oil but nothing ferrous. I also noted in the process that the RH fork only provides compression damping, and a small amount at that, so it seems the ESA-controlled LH fork does most of the damping work. Probably a good thing, considering how clever and reactive the ESA is—wouldn’t want to dumb it down to much with the conventional RH damper,

As I went through the process I proofed my dot points, amending and adding helpful hints along the way. When it came time for refilling, I double checked the noted oil levels against the BMW RSD.EXE. It was then I noticed what I believe to be an anomaly in the RSD. In both cases (left and right) the oil level is specified with the spring and spacer removed and with forks and damper unit fully compressed. The Haynes manual is silent on the damper rod; at my last change I was following the Haynes manual and simply accepted their default position—RH fully compressed and LH in its naturally extended position. The LH damper is spring loaded, taking quite an effort to compress and hold down. It is possible to extend it further than its rest position but looking at the RSD, no special tool is applied to the damper rod to either compress or extend it, and the picture shows it extended. My bet is that the level should be measured with the rod in its natural resting place—something got lost between Showa and the technical documentation writer’s output. Does anyone have a later version of the RSD than 2015 to see whether there has been any amendment?

Of course what you are all waiting for is the answer to the obvious question—is the gold standard BMW fork oil different and potentially better than the Castrol 10W I had just changed out. Well, the answer is (a qualified) YES.

Surprisingly even at low temperature, where the BMW oil is apparently more viscous, the forks felt suppler. The viscosity/temperature relationship is not linear as might be implied by my graph, and at higher temperatures, it seems the BMW oil is less viscous, although it is impossible from my simple testing to determine the crossover point.

This is where the qualification comes in. When changing the forks, the vacant space above the oil is filled with air. My experience with older bikes is that with normal use, some of this air bleeds out, reducing the air-spring effect. I don’t know, however, how pronounced this effect is on the Roadster-LC, given that the forks are well sealed top and bottom.

Also, thus far I’ve ridden only in Road ESA mode and only within the Canberra ‘burbs—relatively well paved and speed limited to a max of 80 km/h, although I have taken some minor liberties for the sake of road testing. Despite the more supple ride, the bike retains its composure entering turns, which was the most significant improvement between the original fill on my bike (presumably Type 1 BMW 7.5W) and the Castrol 10W—with the former, the front end felt like it was falling away a little as the forks quickly compressed before settling, reducing confidence on entry for that millisecond or three. Of course Dynamic ESA mode was taut whatever the oil.

The effect of the ESA compensation also seems more pronounced—the feeling that the bike should be reacting more to road inputs like bumps, but eerily remaining fully composed and seemingly floating where it should be reacting. I expect this will add confidence when out in the twisties where there are bumps and dips that would otherwise require more concentration to cope with. In addition, I can’t feel road imperfections through the ‘bars to the extent that I could with the Castrol.

Overall, therefore (at this stage) the ride is suppler, more comfortable and better controlled than with the Castrol, which itself was an improvement over the BMW 7.5W Type 1, albeit a somewhat cruder one than the new BMW oil.

All this has made the bike even more delightful to ride: 60,000 km service complete, everything within spec, valve clearances barely moved, and improved suspension. I liken it to a spa retreat getaway with your wife, returning refreshed both physically and in your relationship. Don’t tell my wife I said that—she already wonders too much about me (and will want us to go on one of those retreats …).
 

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Fork Oil Change Steps

While the Haynes manual provides a useful narrative of the fork oil change, I found it a little hard to keep track within the text while actually doing the job. To assist, I typed up a checklist of steps, shared for your convenience. It should be read in conjunction with the Haynes manual (or BMW RSD.EXE).

Let me know if you find any anomalies.
 

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I had decided, after reading @Panzermann's helpful writeup, that I would do the fork oil change myself when the time came. I even purchased the required 32mm wrench ahead of time.

Well, the time came recently and there was nothing for it but to dig in. To say that my effort went much like Panzermann's would be to, well, lie, and to engage in some fantastical fun-house mirror thinking. Picture his beautiful, symmetrical top nut tape wrap job. OK. Now picture what would happen if you had your 3-year-old do the job for you, with assistance from the dog. Now you're picturing what I did.

Job 1 with those pretty aluminum top nuts is to not ding them up, so I inserted job 0.5 ahead of that and went ahead and dinged the ESA nut on the left fork. This was not because of my "creative" taping job, but because I only recently learned to read and I missed the important step of loosening the top clamp before trying to loosen the nut. This caused me to really put some torque to the nut, cutting through the tape and, I swear, making the ESA nut whimper a bit. I will give myself some credit for stopping at that point and engaging my brain. I try to conserve it where I can.

The rest of the process went more smoothly, though I wouldn't want to see video of my lurching, fumbling efforts. For example, I made the hold down tool twice, because I made the first one too narrow. It was just some bent steel bar with holes drilled, but still. The strap I used to snug the spring down using Panzermann's excellent method was a little small and made the job harder than necessary. It got the job done, but I had to dig into the Band-Aids after yanking on it.

I used BMW's new 11.5w oil because of Panzermann's positive review. Even if it is a bit pricey at $22/liter, you get to weigh that against the >$300 BMW charges to do this job. :surprise:

Here's a good reminder when reassembling the wheel and brakes: make sure you fasten the speed sensor bracket that has an inside screw before you mount the axle and wheel!

I should have a few years before this job comes up again. I only hope my brain retains some of the lessons learned so I don't go at it cold! Even if memory fails, at least I'll have Panzermann's excellent instructions and pictures to help again!
 

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OK. Now picture what would happen if you had your 3-year-old do the job for you, with assistance from the dog. Now you're picturing what I did.
My repair jobs mimic the joke, “Mommy, can I help dad work on the car? I know all the words.”

I used BMW's new 11.5w oil because of Panzermann's positive review. Even if it is a bit pricey at $22/liter, you get to weigh that against the >$300 BMW charges to do this job. :surprise:
I never skimp on fluids...especially if they are rarely changed.
 

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Fork oil change...

Ah, the days of old when BMW had drain caps on the Airheads and the K bikes.


Changing fork oil back then was a breeze.
 

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Well, approaching 18,000miles, currently at 17,000miles. Should I be dreading this? Biting finger nails. I have noticed the bike has been diving harder than in the past the last 1,000 miles or so.

Are there other seals/washers that need to be changed with this or just oil at this mileage? I did see a tad bit of oil on the inner fork, cleaned it and I haven't seen it for now. Without turning this into an oil thread (maybe too late), liqui moly 10W good enough or Panzerman you would stick with the BMW 11.5 and sold on it for the life of the bike :)?
 
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