2017 X SDBV Forks, oil change.

[MatBin 5,075]

Assuming anyone reading this knows how to remove front wheel, mudguard, brake caliper and handlebars I will concern myself with what I did to the forks.

First off I checked the manual to find out how much fluid I was going to need, 517cc per leg, so ordered 1.5ltrs from Sportsbikeshop, 10w medium weight, which was delivered super quick.

So having supported the middle of the bike under the sump with hydraulic bottle jack and a bit of MDF to spread the load I undid the lower triple clamp bolts (14mm) and the top pinch bolts (6mm hex socket heads). Pushed one upper fork leg clear of plastic around the steering head etc so I could get a 38mm open ended spanner (Neilson combo spanner, from the auction site) onto the top fork nut to 'crack' it open, having re-tightened the lower clamp bolt to hold the fork leg tight. Then undid lower clamp bolt and slid out the complete fork.

Removed top nut, remove spacer, 2 washers, spring (noting tight coils at the bottom) and drained old oil into a measuring jug, compressing lower and upper fork legs several times to get 'all' of the fluid out, let it drain for a while into the jug then stuffed tissue into the leg and inverted it and stored in my shed to get any remaing fluid out.

Old fluid in jug measured 400cc, hmmm! Web reckons 140mm air gap, so poured 500cc into new measuring jug as a starting point at least.

Got a 140mm measuring device, poured most of the new oil into the fork, with stanchion compressed into the slider and measured a 140 air gap. Used about 430cc of fresh oil, hmmm!

Re-assembled the components but placed washer above and below spring, as opposed to 2 above. The oil that came out was brown, so not sure if it's been replaced before.

PT 2 to follow.

Placed leg back in bike, reverse of removal including nipping up top fork nut.

Removed second leg, but this time measured existing air gap, approx 185mm.

Repeated as for first leg and replaced on bike as per first leg.

Made sure both top nuts sat in same place in top clamp.

I also gave both stanchions a good seeing to with chrome cleaner as there were rusty marks and pits, above fork travel line. I fitted Triumph fork deflectors a while back but original owner had not protected stanchions at all, and it shows.

Replaced everything else, including rotating bars back a little.

Test ride - I think the forks are better at handling severe road imperfections without crashing, they seem to hop over the wicked road surfaces I encounter in Herts, but perhaps now show up the rear unit being oversprung.

Handling seems fine, as good as before but with a slightly less jarring ride from the front end. Tempted to say that whilst not as plush as my previous Triumph GT 1050 SE they are at least now pretty acceptable for a budget bike.

I weigh 13st without my bike kit on and 5'-11" tall for reference. Not the fastest or maybe slowest theses days.

Edited August 18, 2021 by MatBin

[skorpion 945]

Happy you've found a setting that works for you.

 

2016-2020  NC750X SDBV standard fork oil air gap is 180mm UK version.

 

Personally I find 500ml of oil in each leg works better for me (less dive) though I'm a bit of a lard a--e. lol

 

[MatBin 5,075]

36 minutes ago, skorpion said:

Happy you've found a setting that works for you.

 

2016-2020  NC750X SDBV standard fork oil air gap is 180mm UK version.

 

Personally I find 500ml of oil in each leg works better for me (less dive) though I'm a bit of a lard a--e. lol

 

500ml results in a very small air gap I presume?

Some people like BM suspension because it doesn't dive, I like diving suspension, to me it confirms weight transfer onto the front wheel and allows heavy braking.

[fred_jb 10,264]

13 hours ago, MatBin said:

500ml results in a very small air gap I presume?

Some people like BM suspension because it doesn't dive, I like diving suspension, to me it confirms weight transfer onto the front wheel and allows heavy braking.

I don't think the lack of dive on some BMW bikes equipped with Telelever front suspension prevents weight transfer and heavy braking. In my experience you can still brake hard.

 

What it does do is stop braking from using up all your suspension travel, thereby allowing the bike's suspension to continue to absorb bumps while braking, which has to be good for stability and comfort.

[MatBin 5,075]

26 minutes ago, fred_jb said:

I don't think the lack of dive on some BMW bikes equipped with Telelever front suspension prevents weight transfer and heavy braking. In my experience you can still brake hard.

 

What it does do is stop braking from using up all your suspension travel, thereby allowing the bike's suspension to continue to absorb bumps while braking, which has to be good for stability and comfort.

Good point. I rode a Honda 50 with trailing link suspension that rode up when braking, hated that

guess after 50 years biking I am stuck in my ways, but you still see 'conventional' teles on race bikes, if BMW system was better I should have expected someone to be using it in road racing, maybe it's just better for a non racing situation?

Edited August 19, 2021 by MatBin

[fred_jb 10,264]

1 hour ago, MatBin said:

Good point. I rode a Honda 50 with trailing link suspension that rode up when braking, hated that

guess after 50 years biking I am stuck in my ways, but you still see 'conventional' teles on race bikes, if BMW system was better I should have expected someone to be using it in road racing, maybe it's just better for a non racing situation?

 

I think with electronically controlled suspension, which is becoming the norm these days, the compression damping on conventional forks can be instantly increased under braking to reduce dive, though still at the expense of less responsive suspension under heavy braking.

 

In the case of race bikes I believe that the change in geometry under braking due to suspension compression actually helps a little with turn in on corners, though I suspect race bikes have very stiff suspension anyway.

 

I think the Telelever system is good for road bikes, but not so much better as to outweigh the packaging difficulties the long front wishbone presents.  It can be accommodated on the boxer engined bikes but would be more difficult with other engine layouts. It also has to use a flexible coupling at the top of the telescopic struts to accommodate a change of angle at the bottom link which moves in an arc as the wishbone rise and falls.  Some say the system has a vague steering feel, which might be due to this.

 

Most other BMWs now use conventional forks with the exception of the K1600 which uses a compact dual wishbone type system, similar to the one now used on Honda's latest Goldwing.  I have owned the GS which has Telelever and the RS which has the same engine but conventional forks, and actually preferred the RS, but then I am not a very demanding rider, so wouldn't push either system to anywhere near its limits!

[jeremyr62 2,530]

On the subject of the new fangled dynamically adjustable damping suspension we see appearing on bikes these days, I can't help feeling for the vast majority it's over complication and will make servicing and maintenance horribly expensive. When the bike is new and shiny no problem, but after a few years riding in European winters all those electronic screwdrivers might be screwing no more. That was one of the reasons I got rid of my FJR1300 ES version. 

 

I remember the fad for anti-dive in the eighties. Never did much in my experience.

[fred_jb 10,264]

Interesting to hear of your efforts to improve the NC suspension.

 

I had a 2015 model and found the suspension far too hard.  I have a stretch of road nearby with a very broken surface and found that every jolt was faithfully transmitted to my wrists by the front suspension and to my backside by the rear.

 

I eventually fitted fully adjustable Andreani inserts to the front and a Wilbers shock to the rear which was a big improvement, but probably not worth the cost as I sold the bike about a year later!

[MatBin 5,075]

1 hour ago, fred_jb said:

Interesting to hear of your efforts to improve the NC suspension.

 

I had a 2015 model and found the suspension far too hard.  I have a stretch of road nearby with a very broken surface and found that every jolt was faithfully transmitted to my wrists by the front suspension and to my backside by the rear.

 

I eventually fitted fully adjustable Andreani inserts to the front and a Wilbers shock to the rear which was a big improvement, but probably not worth the cost as I sold the bike about a year later!

I checked the tech spec of both the Honda recommended fluid and the fluid I used, Liqui Moly 10w, and it looks like the Honda stuff is 'stiffer', so using Moly and decreasing the air gap may have resulted in a quicker acting and quicker stiffening shock absorber thereby not jarring as easily, but what do I know?

[Steve Case 939]

The book that cannot be named says 2017 uses 517cm3 and the fluid level is 4" or 101mm from the fork top with the forks fully compressed (no spring).

I'll be trying the liquid moly 10w tho!

[skorpion 945]

1 hour ago, Steve Case said:

The book that cannot be named says 2017 uses 517cm3 and the fluid level is 4" or 101mm from the fork top with the forks fully compressed (no spring).

I'll be trying the liquid moly 10w tho!

 

That figure is not for the SDBV forks, but but for standard forks fitted in the UK before 2016 and also other parts of the world that didn't get the SDBV forks.

[NickT 9]

Nice description of doing the fork oil - of itself an excellent reason for having a centre stand!

 

A question for you all - with nice knife edge seals on the fork legs, how does the dirt get in to change the fork oil colour?  

[fred_jb 10,264]

1 hour ago, NickT said:

Nice description of doing the fork oil - of itself an excellent reason for having a centre stand!

 

A question for you all - with nice knife edge seals on the fork legs, how does the dirt get in to change the fork oil colour?  

Maybe oxidation as the oil is worked hard, and chemical breakdown over time of the oil or additives?

[jeremyr62 2,530]

Wear of the bearing surfaces I expect. I don't think the fact it is dirty is what matters so much as the change in viscosity. I have yet to see any sensible evidence the viscosity of fork oil changes significantly with use. I am not saying it doesn't, just that I have never seen evidence other than anecdotal.

[NickT 9]

I think fork oil gets a quiet life compared to engine oil - low number of cycles, near ambient temperature. Next time I change it, I'll run the old an new through a viscosity cup and see if there is any difference...

 

[skorpion 945]

In my experience with the NC the fork oil is dark brown within 1000 miles or less,

no need to worry unless draining brings with it large amount of metallic particles.

[trisaki 2,029]

140 mm air gap was for the pre 16 model (700x and 750x)   std was 104 mm but I found  140mm was so much nicer and less jarring  

[MatBin 5,075]

6 hours ago, Steve Case said:

The book that cannot be named says 2017 uses 517cm3 and the fluid level is 4" or 101mm from the fork top with the forks fully compressed (no spring).

I'll be trying the liquid moly 10w tho!

@skorpion above says 180mm air gap and mine (2017 sdbv type) was very close to that, and at 4 yes old, sold to me at 3 yes low mileage probably hadn't been changed since new, glad I settled on 140 as a first guess  The yank suspension expert reckons it's fine to experiment and so long as it doesn't bottom out it's ok.

Liqui (no d) Moly from Sportsbikeshop. Volume wise I reckon about 430cc for the 140mm air gap (or 400 for 180), so I would think 517cc and it will overflow the fork leg!

I guess tyres, tyre pressure, rider weight, rear suspension setting and condition of shock plus local ride surfaces are all variables over and above fork oil viscosity/weight, so what suits one rider may not suit another, especially if we take into consideration rider style. A mine field to be sure.

[Steve Case 939]

Those are some varied values, makes me wonder if they are all measured the same way. The manual is explicit in that the fork is removed from the bike, the spring is removed from the fork and the fork stanchion has been slid all the way down into the lower/slider i.e. its shortest possible length.

 

Is that the same measurement everyone is making? The only difference for me is the fork at its shortest length as I've not done that before.

[MatBin 5,075]

3 hours ago, Steve Case said:

Those are some varied values, makes me wonder if they are all measured the same way. The manual is explicit in that the fork is removed from the bike, the spring is removed from the fork and the fork stanchion has been slid all the way down into the lower/slider i.e. its shortest possible length.

 

Is that the same measurement everyone is making? The only difference for me is the fork at its shortest length as I've not done that before.

That's the way I did it, fork at shortest length, this actually resulted in fork seals going into the pitted area of the stanchion which doesn't happen when riding.

[RoyG 233]

This is all a bit confusing for a simple Brummie. I have a 2012 x and I intend to stick Half a litre in each fork. Anyone think this is a bad idea ?

[Steve Case 939]

Your not wrong, I have a 2017 with the fairly average SDBV forks. So unless different forks were used for different markets I cannot see how the information for the 2016-2017 bike is wrong in the service manual. But....

 

I will follow Matts and others lead and empty the forks into a measuring jug and I will get a height measurement, both will be approx.  but since the operation of the forks is fairly approximate it can only be improved.

 

Does beg the question how the fork action can be nowhere near as good as the 700 Transalp when the forks are supposed to be better?

[Defender 3,825]

4 minutes ago, Steve Case said:

Your not wrong, I have a 2017 with the fairly average SDBV forks. So unless different forks were used for different markets I cannot see how the information for the 2016-2017 bike is wrong in the service manual. But....

I will follow Matts and others lead and empty the forks into a measuring jug and I will get a height measurement, both will be approx. but since the operation of the forks is fairly approximate it can only be improved.

Does beg the question how the fork action can be nowhere near as good as the 700 Transalp when the forks are supposed to be better?

I could be wrong, but I think that the 700 Transalp had longer travel forks, with a longer stroke the limitation/short comings could be less apparent?

I love your description of the fork operation as being 'fairly approximate it can only be improved', I think you hit the nail on the head there!

I have modified non SDBV forks on my 2012 NC700X' they are certainly better than the original spec ones that came out. they might need a bit of fine tuning along with the rear YSS shock to get the best overall ride. 

[Steve Case 939]

Thanks for that, the Transalp was a better ride but one thing that sticks in my mind is the front end was softer, which is realistically what I'm aiming for with this bike.

 

As other people have said its probably down to initial setup at the factory and how we in blighty like a sporty ride so the forks have to be 'firm'. I've also noticed that a lot of bikes are set up firm at the front and soft at the rear which I've never got my head round.

[MatBin 5,075]

20 hours ago, RoyG said:

This is all a bit confusing for a simple Brummie. I have a 2012 x and I intend to stick Half a litre in each fork. Anyone think this is a bad idea ?

Not if it works for you.

Drain the forks first though before pouring in new fluid.

 

No idea if mine are firmer or softer following what I have done, it just feels better at the front, possibly worse at the rear.

Might get a Hagon shock for the rear, need more time on the bike to decide, the existing rear shock looks a bit manky, surprised it got through the MOT tbh, but if I fit a new shock I will probably want to protect it in some way. Then again I don't do many miles or ride in the wet or off road.

Edited August 21, 2021 by MatBin